diff --git a/libstdc++-v3/testsuite/20_util/from_chars/double.cc b/libstdc++-v3/testsuite/20_util/from_chars/double.cc
new file mode 100644
index 00000000000..4dc1ca17865
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/from_chars/double.cc
@@ -0,0 +1,1680 @@
+// This file consists of testcases extracted from the MSVC STL testsuite.
+
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// { dg-do run { target c++17 } }
+// { dg-require-effective-target ieee-floats }
+
+#include <charconv>
+
+#include <limits>
+#include <cstring>
+#include <testsuite_hooks.h>
+
+using namespace std;
+
+inline constexpr double double_inf = numeric_limits<double>::infinity();
+
+struct double_from_chars_testcase {
+    const char* input;
+    chars_format fmt;
+    size_t correct_idx;
+    errc correct_ec;
+    double correct_value;
+};
+
+inline constexpr double_from_chars_testcase double_from_chars_test_cases[] = {
+    {"1.000000000000a000", chars_format::hex, 18, errc{}, 0x1.000000000000ap0}, // exact
+    {"1.000000000000a001", chars_format::hex, 18, errc{}, 0x1.000000000000ap0}, // below midpoint, round down
+    {"1.000000000000a800", chars_format::hex, 18, errc{}, 0x1.000000000000ap0}, // midpoint, round down to even
+    {"1.000000000000a801", chars_format::hex, 18, errc{}, 0x1.000000000000bp0}, // above midpoint, round up
+    {"1.000000000000b000", chars_format::hex, 18, errc{}, 0x1.000000000000bp0}, // exact
+    {"1.000000000000b001", chars_format::hex, 18, errc{}, 0x1.000000000000bp0}, // below midpoint, round down
+    {"1.000000000000b800", chars_format::hex, 18, errc{}, 0x1.000000000000cp0}, // midpoint, round up to even
+    {"1.000000000000b801", chars_format::hex, 18, errc{}, 0x1.000000000000cp0}, // above midpoint, round up
+
+    {"1.00000000000020", chars_format::hex, 16, errc{}, 0x1.0000000000002p0}, // exact
+    {"1.00000000000021", chars_format::hex, 16, errc{}, 0x1.0000000000002p0}, // below midpoint, round down
+    {"1.00000000000028", chars_format::hex, 16, errc{}, 0x1.0000000000002p0}, // midpoint, round down to even
+    {"1.00000000000029", chars_format::hex, 16, errc{}, 0x1.0000000000003p0}, // above midpoint, round up
+    {"1.00000000000030", chars_format::hex, 16, errc{}, 0x1.0000000000003p0}, // exact
+    {"1.00000000000031", chars_format::hex, 16, errc{}, 0x1.0000000000003p0}, // below midpoint, round down
+    {"1.00000000000038", chars_format::hex, 16, errc{}, 0x1.0000000000004p0}, // midpoint, round up to even
+    {"1.00000000000039", chars_format::hex, 16, errc{}, 0x1.0000000000004p0}, // above midpoint, round up
+
+    {"1.00000000000000044408920985006261616945266723632812500000", chars_format::general, 58, errc{},
+        0x1.0000000000002p0}, // exact
+    {"1.00000000000000045796699765787707292474806308746337890625", chars_format::general, 58, errc{},
+        0x1.0000000000002p0}, // below midpoint, round down
+    {"1.00000000000000055511151231257827021181583404541015624999", chars_format::general, 58, errc{},
+        0x1.0000000000002p0}, // below midpoint, round down
+    {"1.00000000000000055511151231257827021181583404541015625000", chars_format::general, 58, errc{},
+        0x1.0000000000002p0}, // midpoint, round down to even
+    {"1.00000000000000055511151231257827021181583404541015625001", chars_format::general, 58, errc{},
+        0x1.0000000000003p0}, // above midpoint, round up
+    {"1.00000000000000056898930012039272696711122989654541015625", chars_format::general, 58, errc{},
+        0x1.0000000000003p0}, // above midpoint, round up
+    {"1.00000000000000066613381477509392425417900085449218750000", chars_format::general, 58, errc{},
+        0x1.0000000000003p0}, // exact
+    {"1.00000000000000068001160258290838100947439670562744140625", chars_format::general, 58, errc{},
+        0x1.0000000000003p0}, // below midpoint, round down
+    {"1.00000000000000077715611723760957829654216766357421874999", chars_format::general, 58, errc{},
+        0x1.0000000000003p0}, // below midpoint, round down
+    {"1.00000000000000077715611723760957829654216766357421875000", chars_format::general, 58, errc{},
+        0x1.0000000000004p0}, // midpoint, round up to even
+    {"1.00000000000000077715611723760957829654216766357421875001", chars_format::general, 58, errc{},
+        0x1.0000000000004p0}, // above midpoint, round up
+    {"1.00000000000000079103390504542403505183756351470947265625", chars_format::general, 58, errc{},
+        0x1.0000000000004p0}, // above midpoint, round up
+
+    // https://www.exploringbinary.com/nondeterministic-floating-point-conversions-in-java/
+    {"0.0000008p-1022", chars_format::hex, 15, errc{}, 0x0.0000008p-1022},
+
+    // VSO-838635 "<charconv>: from_chars() mishandles certain subnormals"
+    // These values change on half-ulp boundaries:
+    // 1 * 2^-1075 ~= 2.47e-324 (half-ulp between zero and min subnormal)
+    // 2 * 2^-1075 ~= 4.94e-324 (min subnormal)
+    // 3 * 2^-1075 ~= 7.41e-324 (half-ulp between min subnormal and next subnormal)
+    // 4 * 2^-1075 ~= 9.88e-324 (next subnormal)
+    {"1."
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111e-324",
+        chars_format::scientific, 1007, errc::result_out_of_range, 0x0.0000000000000p+0},
+    {"2."
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222e-324",
+        chars_format::scientific, 1007, errc::result_out_of_range, 0x0.0000000000000p+0},
+    {"3."
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333"
+     "3333333333333333333e-324",
+        chars_format::scientific, 1007, errc{}, 0x0.0000000000001p-1022},
+    {"4."
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444"
+     "4444444444444444444e-324",
+        chars_format::scientific, 1007, errc{}, 0x0.0000000000001p-1022},
+    {"5."
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"
+     "5555555555555555555e-324",
+        chars_format::scientific, 1007, errc{}, 0x0.0000000000001p-1022},
+    {"6."
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666e-324",
+        chars_format::scientific, 1007, errc{}, 0x0.0000000000001p-1022},
+    {"7."
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777e-324",
+        chars_format::scientific, 1007, errc{}, 0x0.0000000000002p-1022},
+    {"8."
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888e-324",
+        chars_format::scientific, 1007, errc{}, 0x0.0000000000002p-1022},
+    {"9."
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999e-324",
+        chars_format::scientific, 1007, errc{}, 0x0.0000000000002p-1022},
+
+    // VSO-852024: Test cases for round-to-nearest, ties-to-even.
+    // Consider the values:
+    // A: 0x1.0000000000000p+0 == 1.0000000000000000000000000000000000000000000000000000
+    // X:    (1 + 2^-53) * 2^0 == 1.00000000000000011102230246251565404236316680908203125
+    // B: 0x1.0000000000001p+0 == 1.0000000000000002220446049250313080847263336181640625
+    // X is equidistant from A and B. Because they're tied for being nearest, we need to round to even.
+    // That means rounding down to A, because A's least significant hexit 0 is even.
+    // However, values between X and B aren't tied - they're simply nearer to B, so they need to round up to B.
+    // We need to handle tricky cases like the digits of X, followed by a million 0 digits, followed by a 1 digit.
+    // Similarly:
+    // E:      0x1.ffffffffffffep+0 == 1.999999999999999555910790149937383830547332763671875
+    // Y: (1 + 1 - 3 * 2^-53) * 2^0 == 1.99999999999999966693309261245303787291049957275390625
+    // F:      0x1.fffffffffffffp+0 == 1.9999999999999997779553950749686919152736663818359375
+    // The hexit E is 14 and even, while F is 15 and odd.
+
+    // just below (0 + 2^-53) * 2^-1022: decremented last digit, then appended three 9 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002470"
+     "3282292062327208828439643411068618252990130716238221279284125033775363510437593264991818081799618989828234772"
+     "2858865463328355177969898199387398005390939063150356595155702263922908583924491051844359318028499365361525003"
+     "1937045767824921936562366986365848075700158576926990370631192827955855133292783433840935197801553124659726357"
+     "9574622766465272827220056374006485499977096599470454020828166226237857393450736339007967761930577506740176324"
+     "6736009689513405355374585166611342237666786041621596804619144672918403005300575308490487653917113865916462395"
+     "2491262365388187963623937328042389101867234849766823508986338858792562830275599565752445550725518931369083625"
+     "4779186948667994968324049705821028513185451396213837722826145437693412532098591327667236328124999",
+        chars_format::fixed, 1080, errc::result_out_of_range, 0x0.0000000000000p+0},
+
+    // (0 + 2^-53) * 2^-1022 exactly
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002470"
+     "3282292062327208828439643411068618252990130716238221279284125033775363510437593264991818081799618989828234772"
+     "2858865463328355177969898199387398005390939063150356595155702263922908583924491051844359318028499365361525003"
+     "1937045767824921936562366986365848075700158576926990370631192827955855133292783433840935197801553124659726357"
+     "9574622766465272827220056374006485499977096599470454020828166226237857393450736339007967761930577506740176324"
+     "6736009689513405355374585166611342237666786041621596804619144672918403005300575308490487653917113865916462395"
+     "2491262365388187963623937328042389101867234849766823508986338858792562830275599565752445550725518931369083625"
+     "4779186948667994968324049705821028513185451396213837722826145437693412532098591327667236328125",
+        chars_format::fixed, 1077, errc::result_out_of_range, 0x0.0000000000000p+0},
+
+    // (0 + 2^-53) * 2^-1022 exactly, followed by a thousand 0 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002470"
+     "3282292062327208828439643411068618252990130716238221279284125033775363510437593264991818081799618989828234772"
+     "2858865463328355177969898199387398005390939063150356595155702263922908583924491051844359318028499365361525003"
+     "1937045767824921936562366986365848075700158576926990370631192827955855133292783433840935197801553124659726357"
+     "9574622766465272827220056374006485499977096599470454020828166226237857393450736339007967761930577506740176324"
+     "6736009689513405355374585166611342237666786041621596804619144672918403005300575308490487653917113865916462395"
+     "2491262365388187963623937328042389101867234849766823508986338858792562830275599565752445550725518931369083625"
+     "4779186948667994968324049705821028513185451396213837722826145437693412532098591327667236328125000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000",
+        chars_format::fixed, 2077, errc::result_out_of_range, 0x0.0000000000000p+0},
+
+    // above (0 + 2^-53) * 2^-1022: appended a thousand 0 digits followed by a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002470"
+     "3282292062327208828439643411068618252990130716238221279284125033775363510437593264991818081799618989828234772"
+     "2858865463328355177969898199387398005390939063150356595155702263922908583924491051844359318028499365361525003"
+     "1937045767824921936562366986365848075700158576926990370631192827955855133292783433840935197801553124659726357"
+     "9574622766465272827220056374006485499977096599470454020828166226237857393450736339007967761930577506740176324"
+     "6736009689513405355374585166611342237666786041621596804619144672918403005300575308490487653917113865916462395"
+     "2491262365388187963623937328042389101867234849766823508986338858792562830275599565752445550725518931369083625"
+     "4779186948667994968324049705821028513185451396213837722826145437693412532098591327667236328125000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00001",
+        chars_format::fixed, 2078, errc{}, 0x0.0000000000001p-1022},
+
+    // above (0 + 2^-53) * 2^-1022: appended a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002470"
+     "3282292062327208828439643411068618252990130716238221279284125033775363510437593264991818081799618989828234772"
+     "2858865463328355177969898199387398005390939063150356595155702263922908583924491051844359318028499365361525003"
+     "1937045767824921936562366986365848075700158576926990370631192827955855133292783433840935197801553124659726357"
+     "9574622766465272827220056374006485499977096599470454020828166226237857393450736339007967761930577506740176324"
+     "6736009689513405355374585166611342237666786041621596804619144672918403005300575308490487653917113865916462395"
+     "2491262365388187963623937328042389101867234849766823508986338858792562830275599565752445550725518931369083625"
+     "47791869486679949683240497058210285131854513962138377228261454376934125320985913276672363281251",
+        chars_format::fixed, 1078, errc{}, 0x0.0000000000001p-1022},
+
+    // above (0 + 2^-53) * 2^-1022: incremented last digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002470"
+     "3282292062327208828439643411068618252990130716238221279284125033775363510437593264991818081799618989828234772"
+     "2858865463328355177969898199387398005390939063150356595155702263922908583924491051844359318028499365361525003"
+     "1937045767824921936562366986365848075700158576926990370631192827955855133292783433840935197801553124659726357"
+     "9574622766465272827220056374006485499977096599470454020828166226237857393450736339007967761930577506740176324"
+     "6736009689513405355374585166611342237666786041621596804619144672918403005300575308490487653917113865916462395"
+     "2491262365388187963623937328042389101867234849766823508986338858792562830275599565752445550725518931369083625"
+     "4779186948667994968324049705821028513185451396213837722826145437693412532098591327667236328126",
+        chars_format::fixed, 1077, errc{}, 0x0.0000000000001p-1022},
+
+    // just below (0 + 1 - 3 * 2^-53) * 2^-1022: decremented last digit, then appended three 9 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072006419"
+     "9176395546258779936602667813027328296362349540005779643539444484102225369938322261431279727704724131030539099"
+     "2976863718870946851468024222968583977359185141028540361975476844303195813273469348201130421165308554532083149"
+     "3676067608324920106709384047261543474082573017216837765643921010648239116172158852475760231303527077156200284"
+     "1775343298712758123539074213191978739083589771549597066404661620550578925994422322342444472859570416955675758"
+     "5423752417124134805999073137808018133811049489046686648944255834488901008259721496147104204399198556535697531"
+     "0055231935448663898095485089604066035268185282450207861510244351362091237759797852153577038777504570568436147"
+     "5530270683064113556748943345076587312006145811358486831521563686919762403704226016998291015624999",
+        chars_format::fixed, 1080, errc{}, 0x0.ffffffffffffep-1022},
+
+    // (0 + 1 - 3 * 2^-53) * 2^-1022 exactly
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072006419"
+     "9176395546258779936602667813027328296362349540005779643539444484102225369938322261431279727704724131030539099"
+     "2976863718870946851468024222968583977359185141028540361975476844303195813273469348201130421165308554532083149"
+     "3676067608324920106709384047261543474082573017216837765643921010648239116172158852475760231303527077156200284"
+     "1775343298712758123539074213191978739083589771549597066404661620550578925994422322342444472859570416955675758"
+     "5423752417124134805999073137808018133811049489046686648944255834488901008259721496147104204399198556535697531"
+     "0055231935448663898095485089604066035268185282450207861510244351362091237759797852153577038777504570568436147"
+     "5530270683064113556748943345076587312006145811358486831521563686919762403704226016998291015625",
+        chars_format::fixed, 1077, errc{}, 0x0.ffffffffffffep-1022},
+
+    // (0 + 1 - 3 * 2^-53) * 2^-1022 exactly, followed by a thousand 0 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072006419"
+     "9176395546258779936602667813027328296362349540005779643539444484102225369938322261431279727704724131030539099"
+     "2976863718870946851468024222968583977359185141028540361975476844303195813273469348201130421165308554532083149"
+     "3676067608324920106709384047261543474082573017216837765643921010648239116172158852475760231303527077156200284"
+     "1775343298712758123539074213191978739083589771549597066404661620550578925994422322342444472859570416955675758"
+     "5423752417124134805999073137808018133811049489046686648944255834488901008259721496147104204399198556535697531"
+     "0055231935448663898095485089604066035268185282450207861510244351362091237759797852153577038777504570568436147"
+     "5530270683064113556748943345076587312006145811358486831521563686919762403704226016998291015625000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000",
+        chars_format::fixed, 2077, errc{}, 0x0.ffffffffffffep-1022},
+
+    // above (0 + 1 - 3 * 2^-53) * 2^-1022: appended a thousand 0 digits followed by a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072006419"
+     "9176395546258779936602667813027328296362349540005779643539444484102225369938322261431279727704724131030539099"
+     "2976863718870946851468024222968583977359185141028540361975476844303195813273469348201130421165308554532083149"
+     "3676067608324920106709384047261543474082573017216837765643921010648239116172158852475760231303527077156200284"
+     "1775343298712758123539074213191978739083589771549597066404661620550578925994422322342444472859570416955675758"
+     "5423752417124134805999073137808018133811049489046686648944255834488901008259721496147104204399198556535697531"
+     "0055231935448663898095485089604066035268185282450207861510244351362091237759797852153577038777504570568436147"
+     "5530270683064113556748943345076587312006145811358486831521563686919762403704226016998291015625000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00001",
+        chars_format::fixed, 2078, errc{}, 0x0.fffffffffffffp-1022},
+
+    // above (0 + 1 - 3 * 2^-53) * 2^-1022: appended a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072006419"
+     "9176395546258779936602667813027328296362349540005779643539444484102225369938322261431279727704724131030539099"
+     "2976863718870946851468024222968583977359185141028540361975476844303195813273469348201130421165308554532083149"
+     "3676067608324920106709384047261543474082573017216837765643921010648239116172158852475760231303527077156200284"
+     "1775343298712758123539074213191978739083589771549597066404661620550578925994422322342444472859570416955675758"
+     "5423752417124134805999073137808018133811049489046686648944255834488901008259721496147104204399198556535697531"
+     "0055231935448663898095485089604066035268185282450207861510244351362091237759797852153577038777504570568436147"
+     "55302706830641135567489433450765873120061458113584868315215636869197624037042260169982910156251",
+        chars_format::fixed, 1078, errc{}, 0x0.fffffffffffffp-1022},
+
+    // above (0 + 1 - 3 * 2^-53) * 2^-1022: incremented last digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072006419"
+     "9176395546258779936602667813027328296362349540005779643539444484102225369938322261431279727704724131030539099"
+     "2976863718870946851468024222968583977359185141028540361975476844303195813273469348201130421165308554532083149"
+     "3676067608324920106709384047261543474082573017216837765643921010648239116172158852475760231303527077156200284"
+     "1775343298712758123539074213191978739083589771549597066404661620550578925994422322342444472859570416955675758"
+     "5423752417124134805999073137808018133811049489046686648944255834488901008259721496147104204399198556535697531"
+     "0055231935448663898095485089604066035268185282450207861510244351362091237759797852153577038777504570568436147"
+     "5530270683064113556748943345076587312006145811358486831521563686919762403704226016998291015626",
+        chars_format::fixed, 1077, errc{}, 0x0.fffffffffffffp-1022},
+
+    // just below (1 + 2^-53) * 2^-1022: decremented last digit, then appended three 9 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072016301"
+     "2305563795567615250361241457301801308322872404958664760675944619203679411688695321398552054903200090343478188"
+     "4412325572184367563347617020518175998922941393629966742598285899994830148971433555578567693279306015978183162"
+     "1424250679624607852958851992724935776883207324924799248168692322471659649343292587839501022509739575795105716"
+     "0073834364573849432419299709217920738991976169431413149717326525502008499797367678374315520581880443916381057"
+     "2367791175177756227497413804253387084478193655533073867420834526162513029462022730109054820067654020201547112"
+     "0020281397001415752591234401773622442737124681517501897455599786532342558862196115163359241679580296044770649"
+     "4647018477736093430045142168360701364747951396213837722826145437693412532098591327667236328124999",
+        chars_format::fixed, 1080, errc{}, 0x1.0000000000000p-1022},
+
+    // (1 + 2^-53) * 2^-1022 exactly
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072016301"
+     "2305563795567615250361241457301801308322872404958664760675944619203679411688695321398552054903200090343478188"
+     "4412325572184367563347617020518175998922941393629966742598285899994830148971433555578567693279306015978183162"
+     "1424250679624607852958851992724935776883207324924799248168692322471659649343292587839501022509739575795105716"
+     "0073834364573849432419299709217920738991976169431413149717326525502008499797367678374315520581880443916381057"
+     "2367791175177756227497413804253387084478193655533073867420834526162513029462022730109054820067654020201547112"
+     "0020281397001415752591234401773622442737124681517501897455599786532342558862196115163359241679580296044770649"
+     "4647018477736093430045142168360701364747951396213837722826145437693412532098591327667236328125",
+        chars_format::fixed, 1077, errc{}, 0x1.0000000000000p-1022},
+
+    // (1 + 2^-53) * 2^-1022 exactly, followed by a thousand 0 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072016301"
+     "2305563795567615250361241457301801308322872404958664760675944619203679411688695321398552054903200090343478188"
+     "4412325572184367563347617020518175998922941393629966742598285899994830148971433555578567693279306015978183162"
+     "1424250679624607852958851992724935776883207324924799248168692322471659649343292587839501022509739575795105716"
+     "0073834364573849432419299709217920738991976169431413149717326525502008499797367678374315520581880443916381057"
+     "2367791175177756227497413804253387084478193655533073867420834526162513029462022730109054820067654020201547112"
+     "0020281397001415752591234401773622442737124681517501897455599786532342558862196115163359241679580296044770649"
+     "4647018477736093430045142168360701364747951396213837722826145437693412532098591327667236328125000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000",
+        chars_format::fixed, 2077, errc{}, 0x1.0000000000000p-1022},
+
+    // above (1 + 2^-53) * 2^-1022: appended a thousand 0 digits followed by a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072016301"
+     "2305563795567615250361241457301801308322872404958664760675944619203679411688695321398552054903200090343478188"
+     "4412325572184367563347617020518175998922941393629966742598285899994830148971433555578567693279306015978183162"
+     "1424250679624607852958851992724935776883207324924799248168692322471659649343292587839501022509739575795105716"
+     "0073834364573849432419299709217920738991976169431413149717326525502008499797367678374315520581880443916381057"
+     "2367791175177756227497413804253387084478193655533073867420834526162513029462022730109054820067654020201547112"
+     "0020281397001415752591234401773622442737124681517501897455599786532342558862196115163359241679580296044770649"
+     "4647018477736093430045142168360701364747951396213837722826145437693412532098591327667236328125000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00001",
+        chars_format::fixed, 2078, errc{}, 0x1.0000000000001p-1022},
+
+    // above (1 + 2^-53) * 2^-1022: appended a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072016301"
+     "2305563795567615250361241457301801308322872404958664760675944619203679411688695321398552054903200090343478188"
+     "4412325572184367563347617020518175998922941393629966742598285899994830148971433555578567693279306015978183162"
+     "1424250679624607852958851992724935776883207324924799248168692322471659649343292587839501022509739575795105716"
+     "0073834364573849432419299709217920738991976169431413149717326525502008499797367678374315520581880443916381057"
+     "2367791175177756227497413804253387084478193655533073867420834526162513029462022730109054820067654020201547112"
+     "0020281397001415752591234401773622442737124681517501897455599786532342558862196115163359241679580296044770649"
+     "46470184777360934300451421683607013647479513962138377228261454376934125320985913276672363281251",
+        chars_format::fixed, 1078, errc{}, 0x1.0000000000001p-1022},
+
+    // above (1 + 2^-53) * 2^-1022: incremented last digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072016301"
+     "2305563795567615250361241457301801308322872404958664760675944619203679411688695321398552054903200090343478188"
+     "4412325572184367563347617020518175998922941393629966742598285899994830148971433555578567693279306015978183162"
+     "1424250679624607852958851992724935776883207324924799248168692322471659649343292587839501022509739575795105716"
+     "0073834364573849432419299709217920738991976169431413149717326525502008499797367678374315520581880443916381057"
+     "2367791175177756227497413804253387084478193655533073867420834526162513029462022730109054820067654020201547112"
+     "0020281397001415752591234401773622442737124681517501897455599786532342558862196115163359241679580296044770649"
+     "4647018477736093430045142168360701364747951396213837722826145437693412532098591327667236328126",
+        chars_format::fixed, 1077, errc{}, 0x1.0000000000001p-1022},
+
+    // just below (1 + 1 - 3 * 2^-53) * 2^-1022: decremented last digit, then appended three 9 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000044501477170144020250"
+     "8199667279499186358524265859260511351695091228726223124931264069530541271189424317838013700808305231545782515"
+     "4530323827726959236845743044099361970891187471508150509418060480375117378320411851935338796416115205148741308"
+     "3163272520124606023105869053620631175265621765214646643181420505164043632222668006474326056011713528291579642"
+     "2274554896821334728738317548403413978098469341510556195293821919814730032341053661708792231510873354131880491"
+     "1055533902788485678121901775450062980622457102958163711745945687733011032421168917765671370549738710820782247"
+     "7584250967061891687062782163335299376138075114200886249979505279101870966346394401564490729731565935244123171"
+     "5398102212132212018470035807616260163568645811358486831521563686919762403704226016998291015624999",
+        chars_format::fixed, 1080, errc{}, 0x1.ffffffffffffep-1022},
+
+    // (1 + 1 - 3 * 2^-53) * 2^-1022 exactly
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000044501477170144020250"
+     "8199667279499186358524265859260511351695091228726223124931264069530541271189424317838013700808305231545782515"
+     "4530323827726959236845743044099361970891187471508150509418060480375117378320411851935338796416115205148741308"
+     "3163272520124606023105869053620631175265621765214646643181420505164043632222668006474326056011713528291579642"
+     "2274554896821334728738317548403413978098469341510556195293821919814730032341053661708792231510873354131880491"
+     "1055533902788485678121901775450062980622457102958163711745945687733011032421168917765671370549738710820782247"
+     "7584250967061891687062782163335299376138075114200886249979505279101870966346394401564490729731565935244123171"
+     "5398102212132212018470035807616260163568645811358486831521563686919762403704226016998291015625",
+        chars_format::fixed, 1077, errc{}, 0x1.ffffffffffffep-1022},
+
+    // (1 + 1 - 3 * 2^-53) * 2^-1022 exactly, followed by a thousand 0 digits
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000044501477170144020250"
+     "8199667279499186358524265859260511351695091228726223124931264069530541271189424317838013700808305231545782515"
+     "4530323827726959236845743044099361970891187471508150509418060480375117378320411851935338796416115205148741308"
+     "3163272520124606023105869053620631175265621765214646643181420505164043632222668006474326056011713528291579642"
+     "2274554896821334728738317548403413978098469341510556195293821919814730032341053661708792231510873354131880491"
+     "1055533902788485678121901775450062980622457102958163711745945687733011032421168917765671370549738710820782247"
+     "7584250967061891687062782163335299376138075114200886249979505279101870966346394401564490729731565935244123171"
+     "5398102212132212018470035807616260163568645811358486831521563686919762403704226016998291015625000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000",
+        chars_format::fixed, 2077, errc{}, 0x1.ffffffffffffep-1022},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^-1022: appended a thousand 0 digits followed by a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000044501477170144020250"
+     "8199667279499186358524265859260511351695091228726223124931264069530541271189424317838013700808305231545782515"
+     "4530323827726959236845743044099361970891187471508150509418060480375117378320411851935338796416115205148741308"
+     "3163272520124606023105869053620631175265621765214646643181420505164043632222668006474326056011713528291579642"
+     "2274554896821334728738317548403413978098469341510556195293821919814730032341053661708792231510873354131880491"
+     "1055533902788485678121901775450062980622457102958163711745945687733011032421168917765671370549738710820782247"
+     "7584250967061891687062782163335299376138075114200886249979505279101870966346394401564490729731565935244123171"
+     "5398102212132212018470035807616260163568645811358486831521563686919762403704226016998291015625000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00001",
+        chars_format::fixed, 2078, errc{}, 0x1.fffffffffffffp-1022},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^-1022: appended a 1 digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000044501477170144020250"
+     "8199667279499186358524265859260511351695091228726223124931264069530541271189424317838013700808305231545782515"
+     "4530323827726959236845743044099361970891187471508150509418060480375117378320411851935338796416115205148741308"
+     "3163272520124606023105869053620631175265621765214646643181420505164043632222668006474326056011713528291579642"
+     "2274554896821334728738317548403413978098469341510556195293821919814730032341053661708792231510873354131880491"
+     "1055533902788485678121901775450062980622457102958163711745945687733011032421168917765671370549738710820782247"
+     "7584250967061891687062782163335299376138075114200886249979505279101870966346394401564490729731565935244123171"
+     "53981022121322120184700358076162601635686458113584868315215636869197624037042260169982910156251",
+        chars_format::fixed, 1078, errc{}, 0x1.fffffffffffffp-1022},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^-1022: incremented last digit
+    {"0."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000044501477170144020250"
+     "8199667279499186358524265859260511351695091228726223124931264069530541271189424317838013700808305231545782515"
+     "4530323827726959236845743044099361970891187471508150509418060480375117378320411851935338796416115205148741308"
+     "3163272520124606023105869053620631175265621765214646643181420505164043632222668006474326056011713528291579642"
+     "2274554896821334728738317548403413978098469341510556195293821919814730032341053661708792231510873354131880491"
+     "1055533902788485678121901775450062980622457102958163711745945687733011032421168917765671370549738710820782247"
+     "7584250967061891687062782163335299376138075114200886249979505279101870966346394401564490729731565935244123171"
+     "5398102212132212018470035807616260163568645811358486831521563686919762403704226016998291015626",
+        chars_format::fixed, 1077, errc{}, 0x1.fffffffffffffp-1022},
+
+    // just below (1 + 2^-53) * 2^-33: decremented last digit, then appended three 9 digits
+    {"0.00000000011641532182693482737782207114105741986576081359316958696581423282623291015624999", chars_format::fixed,
+        91, errc{}, 0x1.0000000000000p-33},
+
+    // (1 + 2^-53) * 2^-33 exactly
+    {"0.00000000011641532182693482737782207114105741986576081359316958696581423282623291015625", chars_format::fixed,
+        88, errc{}, 0x1.0000000000000p-33},
+
+    // (1 + 2^-53) * 2^-33 exactly, followed by a thousand 0 digits
+    {"0."
+     "0000000001164153218269348273778220711410574198657608135931695869658142328262329101562500000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+        chars_format::fixed, 1088, errc{}, 0x1.0000000000000p-33},
+
+    // above (1 + 2^-53) * 2^-33: appended a thousand 0 digits followed by a 1 digit
+    {"0."
+     "0000000001164153218269348273778220711410574198657608135931695869658142328262329101562500000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001",
+        chars_format::fixed, 1089, errc{}, 0x1.0000000000001p-33},
+
+    // above (1 + 2^-53) * 2^-33: appended a 1 digit
+    {"0.000000000116415321826934827377822071141057419865760813593169586965814232826232910156251", chars_format::fixed,
+        89, errc{}, 0x1.0000000000001p-33},
+
+    // above (1 + 2^-53) * 2^-33: incremented last digit
+    {"0.00000000011641532182693482737782207114105741986576081359316958696581423282623291015626", chars_format::fixed,
+        88, errc{}, 0x1.0000000000001p-33},
+
+    // just below (1 + 1 - 3 * 2^-53) * 2^-33: decremented last digit, then appended three 9 digits
+    {"0.00000000023283064365386959013215878657682774040271755922049123910255730152130126953124999", chars_format::fixed,
+        91, errc{}, 0x1.ffffffffffffep-33},
+
+    // (1 + 1 - 3 * 2^-53) * 2^-33 exactly
+    {"0.00000000023283064365386959013215878657682774040271755922049123910255730152130126953125", chars_format::fixed,
+        88, errc{}, 0x1.ffffffffffffep-33},
+
+    // (1 + 1 - 3 * 2^-53) * 2^-33 exactly, followed by a thousand 0 digits
+    {"0."
+     "0000000002328306436538695901321587865768277404027175592204912391025573015213012695312500000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+        chars_format::fixed, 1088, errc{}, 0x1.ffffffffffffep-33},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^-33: appended a thousand 0 digits followed by a 1 digit
+    {"0."
+     "0000000002328306436538695901321587865768277404027175592204912391025573015213012695312500000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001",
+        chars_format::fixed, 1089, errc{}, 0x1.fffffffffffffp-33},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^-33: appended a 1 digit
+    {"0.000000000232830643653869590132158786576827740402717559220491239102557301521301269531251", chars_format::fixed,
+        89, errc{}, 0x1.fffffffffffffp-33},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^-33: incremented last digit
+    {"0.00000000023283064365386959013215878657682774040271755922049123910255730152130126953126", chars_format::fixed,
+        88, errc{}, 0x1.fffffffffffffp-33},
+
+    // just below (1 + 2^-53) * 2^0: decremented last digit, then appended three 9 digits
+    {"1.00000000000000011102230246251565404236316680908203124999", chars_format::fixed, 58, errc{},
+        0x1.0000000000000p+0},
+
+    // (1 + 2^-53) * 2^0 exactly
+    {"1.00000000000000011102230246251565404236316680908203125", chars_format::fixed, 55, errc{}, 0x1.0000000000000p+0},
+
+    // (1 + 2^-53) * 2^0 exactly, followed by a thousand 0 digits
+    {"1."
+     "0000000000000001110223024625156540423631668090820312500000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000000",
+        chars_format::fixed, 1055, errc{}, 0x1.0000000000000p+0},
+
+    // above (1 + 2^-53) * 2^0: appended a thousand 0 digits followed by a 1 digit
+    {"1."
+     "0000000000000001110223024625156540423631668090820312500000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000001",
+        chars_format::fixed, 1056, errc{}, 0x1.0000000000001p+0},
+
+    // above (1 + 2^-53) * 2^0: appended a 1 digit
+    {"1.000000000000000111022302462515654042363166809082031251", chars_format::fixed, 56, errc{}, 0x1.0000000000001p+0},
+
+    // above (1 + 2^-53) * 2^0: incremented last digit
+    {"1.00000000000000011102230246251565404236316680908203126", chars_format::fixed, 55, errc{}, 0x1.0000000000001p+0},
+
+    // just below (1 + 1 - 3 * 2^-53) * 2^0: decremented last digit, then appended three 9 digits
+    {"1.99999999999999966693309261245303787291049957275390624999", chars_format::fixed, 58, errc{},
+        0x1.ffffffffffffep+0},
+
+    // (1 + 1 - 3 * 2^-53) * 2^0 exactly
+    {"1.99999999999999966693309261245303787291049957275390625", chars_format::fixed, 55, errc{}, 0x1.ffffffffffffep+0},
+
+    // (1 + 1 - 3 * 2^-53) * 2^0 exactly, followed by a thousand 0 digits
+    {"1."
+     "9999999999999996669330926124530378729104995727539062500000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000000",
+        chars_format::fixed, 1055, errc{}, 0x1.ffffffffffffep+0},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^0: appended a thousand 0 digits followed by a 1 digit
+    {"1."
+     "9999999999999996669330926124530378729104995727539062500000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000001",
+        chars_format::fixed, 1056, errc{}, 0x1.fffffffffffffp+0},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^0: appended a 1 digit
+    {"1.999999999999999666933092612453037872910499572753906251", chars_format::fixed, 56, errc{}, 0x1.fffffffffffffp+0},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^0: incremented last digit
+    {"1.99999999999999966693309261245303787291049957275390626", chars_format::fixed, 55, errc{}, 0x1.fffffffffffffp+0},
+
+    // just below (1 + 2^-53) * 2^33: decremented last digit, then appended three 9 digits
+    {"8589934592.00000095367431640624999", chars_format::fixed, 34, errc{}, 0x1.0000000000000p+33},
+
+    // (1 + 2^-53) * 2^33 exactly
+    {"8589934592.00000095367431640625", chars_format::fixed, 31, errc{}, 0x1.0000000000000p+33},
+
+    // (1 + 2^-53) * 2^33 exactly, followed by a thousand 0 digits
+    {"8589934592."
+     "0000009536743164062500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000",
+        chars_format::fixed, 1031, errc{}, 0x1.0000000000000p+33},
+
+    // above (1 + 2^-53) * 2^33: appended a thousand 0 digits followed by a 1 digit
+    {"8589934592."
+     "0000009536743164062500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000001",
+        chars_format::fixed, 1032, errc{}, 0x1.0000000000001p+33},
+
+    // above (1 + 2^-53) * 2^33: appended a 1 digit
+    {"8589934592.000000953674316406251", chars_format::fixed, 32, errc{}, 0x1.0000000000001p+33},
+
+    // above (1 + 2^-53) * 2^33: incremented last digit
+    {"8589934592.00000095367431640626", chars_format::fixed, 31, errc{}, 0x1.0000000000001p+33},
+
+    // just below (1 + 1 - 3 * 2^-53) * 2^33: decremented last digit, then appended three 9 digits
+    {"17179869183.99999713897705078124999", chars_format::fixed, 35, errc{}, 0x1.ffffffffffffep+33},
+
+    // (1 + 1 - 3 * 2^-53) * 2^33 exactly
+    {"17179869183.99999713897705078125", chars_format::fixed, 32, errc{}, 0x1.ffffffffffffep+33},
+
+    // (1 + 1 - 3 * 2^-53) * 2^33 exactly, followed by a thousand 0 digits
+    {"17179869183."
+     "9999971389770507812500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000",
+        chars_format::fixed, 1032, errc{}, 0x1.ffffffffffffep+33},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^33: appended a thousand 0 digits followed by a 1 digit
+    {"17179869183."
+     "9999971389770507812500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000001",
+        chars_format::fixed, 1033, errc{}, 0x1.fffffffffffffp+33},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^33: appended a 1 digit
+    {"17179869183.999997138977050781251", chars_format::fixed, 33, errc{}, 0x1.fffffffffffffp+33},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^33: incremented last digit
+    {"17179869183.99999713897705078126", chars_format::fixed, 32, errc{}, 0x1.fffffffffffffp+33},
+
+    // just below (1 + 2^-53) * 2^77: decremented last digit, then appended three 9 digits
+    {"151115727451828663615487.999", chars_format::fixed, 28, errc{}, 0x1.0000000000000p+77},
+
+    // (1 + 2^-53) * 2^77 exactly
+    {"151115727451828663615488", chars_format::fixed, 24, errc{}, 0x1.0000000000000p+77},
+
+    // (1 + 2^-53) * 2^77 exactly, followed by a thousand 0 digits
+    {"151115727451828663615488."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000",
+        chars_format::fixed, 1025, errc{}, 0x1.0000000000000p+77},
+
+    // above (1 + 2^-53) * 2^77: appended a thousand 0 digits followed by a 1 digit
+    {"151115727451828663615488."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000001",
+        chars_format::fixed, 1026, errc{}, 0x1.0000000000001p+77},
+
+    // above (1 + 2^-53) * 2^77: appended a 1 digit
+    {"151115727451828663615488.1", chars_format::fixed, 26, errc{}, 0x1.0000000000001p+77},
+
+    // above (1 + 2^-53) * 2^77: incremented last digit
+    {"151115727451828663615489", chars_format::fixed, 24, errc{}, 0x1.0000000000001p+77},
+
+    // just below (1 + 1 - 3 * 2^-53) * 2^77: decremented last digit, then appended three 9 digits
+    {"302231454903657243344895.999", chars_format::fixed, 28, errc{}, 0x1.ffffffffffffep+77},
+
+    // (1 + 1 - 3 * 2^-53) * 2^77 exactly
+    {"302231454903657243344896", chars_format::fixed, 24, errc{}, 0x1.ffffffffffffep+77},
+
+    // (1 + 1 - 3 * 2^-53) * 2^77 exactly, followed by a thousand 0 digits
+    {"302231454903657243344896."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000",
+        chars_format::fixed, 1025, errc{}, 0x1.ffffffffffffep+77},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^77: appended a thousand 0 digits followed by a 1 digit
+    {"302231454903657243344896."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000001",
+        chars_format::fixed, 1026, errc{}, 0x1.fffffffffffffp+77},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^77: appended a 1 digit
+    {"302231454903657243344896.1", chars_format::fixed, 26, errc{}, 0x1.fffffffffffffp+77},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^77: incremented last digit
+    {"302231454903657243344897", chars_format::fixed, 24, errc{}, 0x1.fffffffffffffp+77},
+
+    // just below (1 + 2^-53) * 2^1023: decremented last digit, then appended three 9 digits
+    {"8988465674311580536566680721305029496276241413130815897397134275615404541548669375241369800602409693534988440"
+     "3114202125541629105369684531108613657287705365884742938136589844238179474556051429647415148697857438797685859"
+     "063890851407391008830874765563025951597582513936655578157348020066364210154316532161708031.999",
+        chars_format::fixed, 312, errc{}, 0x1.0000000000000p+1023},
+
+    // (1 + 2^-53) * 2^1023 exactly
+    {"8988465674311580536566680721305029496276241413130815897397134275615404541548669375241369800602409693534988440"
+     "3114202125541629105369684531108613657287705365884742938136589844238179474556051429647415148697857438797685859"
+     "063890851407391008830874765563025951597582513936655578157348020066364210154316532161708032",
+        chars_format::fixed, 308, errc{}, 0x1.0000000000000p+1023},
+
+    // (1 + 2^-53) * 2^1023 exactly, followed by a thousand 0 digits
+    {"8988465674311580536566680721305029496276241413130815897397134275615404541548669375241369800602409693534988440"
+     "3114202125541629105369684531108613657287705365884742938136589844238179474556051429647415148697857438797685859"
+     "063890851407391008830874765563025951597582513936655578157348020066364210154316532161708032."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000",
+        chars_format::fixed, 1309, errc{}, 0x1.0000000000000p+1023},
+
+    // above (1 + 2^-53) * 2^1023: appended a thousand 0 digits followed by a 1 digit
+    {"8988465674311580536566680721305029496276241413130815897397134275615404541548669375241369800602409693534988440"
+     "3114202125541629105369684531108613657287705365884742938136589844238179474556051429647415148697857438797685859"
+     "063890851407391008830874765563025951597582513936655578157348020066364210154316532161708032."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000001",
+        chars_format::fixed, 1310, errc{}, 0x1.0000000000001p+1023},
+
+    // above (1 + 2^-53) * 2^1023: appended a 1 digit
+    {"8988465674311580536566680721305029496276241413130815897397134275615404541548669375241369800602409693534988440"
+     "3114202125541629105369684531108613657287705365884742938136589844238179474556051429647415148697857438797685859"
+     "063890851407391008830874765563025951597582513936655578157348020066364210154316532161708032.1",
+        chars_format::fixed, 310, errc{}, 0x1.0000000000001p+1023},
+
+    // above (1 + 2^-53) * 2^1023: incremented last digit
+    {"8988465674311580536566680721305029496276241413130815897397134275615404541548669375241369800602409693534988440"
+     "3114202125541629105369684531108613657287705365884742938136589844238179474556051429647415148697857438797685859"
+     "063890851407391008830874765563025951597582513936655578157348020066364210154316532161708033",
+        chars_format::fixed, 308, errc{}, 0x1.0000000000001p+1023},
+
+    // just below (1 + 1 - 3 * 2^-53) * 2^1023: decremented last digit, then appended three 9 digits
+    {"1797693134862315608353258760581052985162070023416521662616611746258695532672923265745300992879465492467506314"
+     "9033587701752208710592698796290627760473556921329019091915239418047621712533496094635638726128664019802903779"
+     "9514183602981511756283727771403830521483963923935633133642802139091669457927874464075218943.999",
+        chars_format::fixed, 313, errc{}, 0x1.ffffffffffffep+1023},
+
+    // (1 + 1 - 3 * 2^-53) * 2^1023 exactly
+    {"1797693134862315608353258760581052985162070023416521662616611746258695532672923265745300992879465492467506314"
+     "9033587701752208710592698796290627760473556921329019091915239418047621712533496094635638726128664019802903779"
+     "9514183602981511756283727771403830521483963923935633133642802139091669457927874464075218944",
+        chars_format::fixed, 309, errc{}, 0x1.ffffffffffffep+1023},
+
+    // (1 + 1 - 3 * 2^-53) * 2^1023 exactly, followed by a thousand 0 digits
+    {"1797693134862315608353258760581052985162070023416521662616611746258695532672923265745300992879465492467506314"
+     "9033587701752208710592698796290627760473556921329019091915239418047621712533496094635638726128664019802903779"
+     "9514183602981511756283727771403830521483963923935633133642802139091669457927874464075218944."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000",
+        chars_format::fixed, 1310, errc{}, 0x1.ffffffffffffep+1023},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^1023: appended a thousand 0 digits followed by a 1 digit
+    {"1797693134862315608353258760581052985162070023416521662616611746258695532672923265745300992879465492467506314"
+     "9033587701752208710592698796290627760473556921329019091915239418047621712533496094635638726128664019802903779"
+     "9514183602981511756283727771403830521483963923935633133642802139091669457927874464075218944."
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000001",
+        chars_format::fixed, 1311, errc{}, 0x1.fffffffffffffp+1023},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^1023: appended a 1 digit
+    {"1797693134862315608353258760581052985162070023416521662616611746258695532672923265745300992879465492467506314"
+     "9033587701752208710592698796290627760473556921329019091915239418047621712533496094635638726128664019802903779"
+     "9514183602981511756283727771403830521483963923935633133642802139091669457927874464075218944.1",
+        chars_format::fixed, 311, errc{}, 0x1.fffffffffffffp+1023},
+
+    // above (1 + 1 - 3 * 2^-53) * 2^1023: incremented last digit
+    {"1797693134862315608353258760581052985162070023416521662616611746258695532672923265745300992879465492467506314"
+     "9033587701752208710592698796290627760473556921329019091915239418047621712533496094635638726128664019802903779"
+     "9514183602981511756283727771403830521483963923935633133642802139091669457927874464075218945",
+        chars_format::fixed, 309, errc{}, 0x1.fffffffffffffp+1023},
+
+    // VSO-852024 also affected hexfloats.
+    {"0.00000000000008p-1022", chars_format::hex, 22, errc::result_out_of_range, 0x0.0000000000000p+0},
+    {"0."
+     "0000000000000800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000001p-1022",
+        chars_format::hex, 1023, errc{}, 0x0.0000000000001p-1022},
+
+    {"0.ffffffffffffe8p-1022", chars_format::hex, 22, errc{}, 0x0.ffffffffffffep-1022},
+    {"0."
+     "ffffffffffffe800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000001p-1022",
+        chars_format::hex, 1023, errc{}, 0x0.fffffffffffffp-1022},
+
+    {"1.00000000000008p+0", chars_format::hex, 19, errc{}, 0x1.0000000000000p+0},
+    {"1."
+     "0000000000000800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000001p+0",
+        chars_format::hex, 1020, errc{}, 0x1.0000000000001p+0},
+
+    {"1.ffffffffffffe8p+0", chars_format::hex, 19, errc{}, 0x1.ffffffffffffep+0},
+    {"1."
+     "ffffffffffffe800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000001p+0",
+        chars_format::hex, 1020, errc{}, 0x1.fffffffffffffp+0},
+
+    {"1.00000000000008p+1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p+1023},
+    {"1."
+     "0000000000000800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000001p+1023",
+        chars_format::hex, 1023, errc{}, 0x1.0000000000001p+1023},
+
+    {"1.ffffffffffffe8p+1023", chars_format::hex, 22, errc{}, 0x1.ffffffffffffep+1023},
+    {"1."
+     "ffffffffffffe800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000001p+1023",
+        chars_format::hex, 1023, errc{}, 0x1.fffffffffffffp+1023},
+
+    // VSO-733765 "<charconv>: [Feedback] double std::from_chars behavior on exponent out of range"
+    // LWG-3081 "Floating point from_chars API does not distinguish between overflow and underflow"
+    // These test cases exercise every overflow/underflow codepath.
+    {"1e+1000", chars_format::scientific, 7, errc::result_out_of_range, double_inf},
+    {"1e-1000", chars_format::scientific, 7, errc::result_out_of_range, 0.0},
+    {"1.fffffffffffff8p+1023", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"1e+2000", chars_format::scientific, 7, errc::result_out_of_range, double_inf},
+    {"1e-2000", chars_format::scientific, 7, errc::result_out_of_range, 0.0},
+    {"1e+9999", chars_format::scientific, 7, errc::result_out_of_range, double_inf},
+    {"1e-9999", chars_format::scientific, 7, errc::result_out_of_range, 0.0},
+    {"10e+5199", chars_format::scientific, 8, errc::result_out_of_range, double_inf},
+    {"0.001e-5199", chars_format::scientific, 11, errc::result_out_of_range, 0.0},
+
+    // GH-931 "<charconv>: hex from_chars(\"0.fffffffffffff8p-1022\") is incorrect"
+    // Test cases for values close to std::numeric_limits<double>::min() and std::numeric_limits<double>::max()
+    {"0.fffffffffffffp-1022", chars_format::hex, 21, errc{}, 0x0.fffffffffffffp-1022},
+    {"1.0000000000000p-1022", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+
+    {"1.ffffffffffffep-1023", chars_format::hex, 21, errc{}, 0x0.fffffffffffffp-1022},
+    {"1.fffffffffffffp-1023", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+    {"2.0000000000000p-1023", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+
+    {"3.ffffffffffffcp-1024", chars_format::hex, 21, errc{}, 0x0.fffffffffffffp-1022},
+    {"3.ffffffffffffdp-1024", chars_format::hex, 21, errc{}, 0x0.fffffffffffffp-1022},
+    {"3.ffffffffffffep-1024", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+    {"3.fffffffffffffp-1024", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+    {"4.0000000000000p-1024", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+
+    {"7.ffffffffffff8p-1025", chars_format::hex, 21, errc{}, 0x0.fffffffffffffp-1022},
+    {"7.ffffffffffff9p-1025", chars_format::hex, 21, errc{}, 0x0.fffffffffffffp-1022},
+    {"7.ffffffffffffbp-1025", chars_format::hex, 21, errc{}, 0x0.fffffffffffffp-1022},
+    {"7.ffffffffffffcp-1025", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+    {"7.ffffffffffffdp-1025", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+    {"7.ffffffffffffep-1025", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+    {"7.fffffffffffffp-1025", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+    {"8.0000000000000p-1025", chars_format::hex, 21, errc{}, 0x1.0000000000000p-1022},
+
+    {"0.fffffffffffff0p-1022", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"0.fffffffffffff1p-1022", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"0.fffffffffffff7p-1022", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"0.fffffffffffff8p-1022", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"0.fffffffffffff9p-1022", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"0.fffffffffffffbp-1022", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"0.fffffffffffffcp-1022", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"0.fffffffffffffdp-1022", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"0.ffffffffffffffp-1022", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"1.00000000000000p-1022", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+
+    {"1.ffffffffffffe0p-1023", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"1.ffffffffffffe1p-1023", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"1.ffffffffffffefp-1023", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"1.fffffffffffff0p-1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"1.fffffffffffff1p-1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"1.fffffffffffff7p-1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"1.fffffffffffff8p-1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"1.fffffffffffff9p-1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"1.ffffffffffffffp-1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"2.00000000000000p-1023", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+
+    {"3.ffffffffffffc0p-1024", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"3.ffffffffffffc1p-1024", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"3.ffffffffffffdfp-1024", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"3.ffffffffffffe0p-1024", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"3.ffffffffffffe1p-1024", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"3.ffffffffffffefp-1024", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"3.fffffffffffff0p-1024", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"3.fffffffffffff1p-1024", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"3.ffffffffffffffp-1024", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"4.00000000000000p-1024", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+
+    {"7.ffffffffffff80p-1025", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"7.ffffffffffff81p-1025", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"7.ffffffffffffbfp-1025", chars_format::hex, 22, errc{}, 0x0.fffffffffffffp-1022},
+    {"7.ffffffffffffc0p-1025", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"7.ffffffffffffc1p-1025", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"7.ffffffffffffdfp-1025", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"7.ffffffffffffe0p-1025", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"7.ffffffffffffe1p-1025", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"7.ffffffffffffffp-1025", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+    {"8.00000000000000p-1025", chars_format::hex, 22, errc{}, 0x1.0000000000000p-1022},
+
+    {"1.fffffffffffffp+1023", chars_format::hex, 21, errc{}, 0x1.fffffffffffffp+1023},
+    {"2.0000000000000p+1023", chars_format::hex, 21, errc::result_out_of_range, double_inf},
+
+    {"3.ffffffffffffep+1022", chars_format::hex, 21, errc{}, 0x1.fffffffffffffp+1023},
+    {"3.fffffffffffffp+1022", chars_format::hex, 21, errc::result_out_of_range, double_inf},
+    {"4.0000000000000p+1022", chars_format::hex, 21, errc::result_out_of_range, double_inf},
+
+    {"7.ffffffffffffcp+1021", chars_format::hex, 21, errc{}, 0x1.fffffffffffffp+1023},
+    {"7.ffffffffffffdp+1021", chars_format::hex, 21, errc{}, 0x1.fffffffffffffp+1023},
+    {"7.ffffffffffffep+1021", chars_format::hex, 21, errc::result_out_of_range, double_inf},
+    {"7.fffffffffffffp+1021", chars_format::hex, 21, errc::result_out_of_range, double_inf},
+    {"8.0000000000000p+1021", chars_format::hex, 21, errc::result_out_of_range, double_inf},
+
+    {"0.fffffffffffff8p+1024", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"0.fffffffffffff9p+1024", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"0.fffffffffffffbp+1024", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"0.fffffffffffffcp+1024", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"0.fffffffffffffdp+1024", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"0.ffffffffffffffp+1024", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"1.00000000000000p+1024", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+
+    {"1.fffffffffffff0p+1023", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"1.fffffffffffff1p+1023", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"1.fffffffffffff7p+1023", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"1.fffffffffffff8p+1023", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"1.fffffffffffff9p+1023", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"1.ffffffffffffffp+1023", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"2.00000000000000p+1023", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+
+    {"3.ffffffffffffe0p+1022", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"3.ffffffffffffe1p+1022", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"3.ffffffffffffefp+1022", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"3.fffffffffffff0p+1022", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"3.fffffffffffff1p+1022", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"3.ffffffffffffffp+1022", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"4.00000000000000p+1022", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+
+    {"7.ffffffffffffc0p+1021", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"7.ffffffffffffc1p+1021", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"7.ffffffffffffdfp+1021", chars_format::hex, 22, errc{}, 0x1.fffffffffffffp+1023},
+    {"7.ffffffffffffe0p+1021", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"7.ffffffffffffe1p+1021", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"7.ffffffffffffffp+1021", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+    {"8.00000000000000p+1021", chars_format::hex, 22, errc::result_out_of_range, double_inf},
+
+    {"0.fffffffffffff80p+1024", chars_format::hex, 23, errc{}, 0x1.fffffffffffffp+1023},
+    {"0.fffffffffffff81p+1024", chars_format::hex, 23, errc{}, 0x1.fffffffffffffp+1023},
+    {"0.fffffffffffffbfp+1024", chars_format::hex, 23, errc{}, 0x1.fffffffffffffp+1023},
+    {"0.fffffffffffffc0p+1024", chars_format::hex, 23, errc::result_out_of_range, double_inf},
+    {"0.fffffffffffffc1p+1024", chars_format::hex, 23, errc::result_out_of_range, double_inf},
+    {"0.fffffffffffffffp+1024", chars_format::hex, 23, errc::result_out_of_range, double_inf},
+    {"1.000000000000000p+1024", chars_format::hex, 23, errc::result_out_of_range, double_inf},
+
+    // (0 + 1 - 2 * 2^-53) * 2^-1022 exactly
+    {"2."
+     "22507385850720088902458687608585988765042311224095946549352480256244000922823569517877588880375915526423097809504"
+     "34312085877387158357291821993020294379224223559819827501242041788969571311791082261043971979604000454897391938079"
+     "19893608152561311337614984204327175103362739154978273159414382813627511383860409424946494228631669542910508020181"
+     "59266421349966065178030950759130587198464239060686371020051087232827846788436319445158661350412234790147923695852"
+     "08321597621066375401613736583044193603714778355306682834535634005074073040135602968046375918583163124224521599262"
+     "54649430083685186171942241764645513713542013221703137049658321015465406803539741790602258950302350193751977303094"
+     "5763173210852507299305089761582519159720757232455434770912461317493580281734466552734375e-308",
+        chars_format::scientific, 773, errc{}, 0x0.fffffffffffffp-1022},
+
+    // (0 + 1 - 2 * 2^-53) * 2^-1022 exactly, followed by a thousand 0 digits
+    {"2."
+     "22507385850720088902458687608585988765042311224095946549352480256244000922823569517877588880375915526423097809504"
+     "34312085877387158357291821993020294379224223559819827501242041788969571311791082261043971979604000454897391938079"
+     "19893608152561311337614984204327175103362739154978273159414382813627511383860409424946494228631669542910508020181"
+     "59266421349966065178030950759130587198464239060686371020051087232827846788436319445158661350412234790147923695852"
+     "08321597621066375401613736583044193603714778355306682834535634005074073040135602968046375918583163124224521599262"
+     "54649430083685186171942241764645513713542013221703137049658321015465406803539741790602258950302350193751977303094"
+     "57631732108525072993050897615825191597207572324554347709124613174935802817344665527343750000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000e-308",
+        chars_format::scientific, 1773, errc{}, 0x0.fffffffffffffp-1022},
+
+    // above (0 + 1 - 2 * 2^-53) * 2^-1022, appended a thousand 0 digits followed by a 1 digit
+    {"2."
+     "22507385850720088902458687608585988765042311224095946549352480256244000922823569517877588880375915526423097809504"
+     "34312085877387158357291821993020294379224223559819827501242041788969571311791082261043971979604000454897391938079"
+     "19893608152561311337614984204327175103362739154978273159414382813627511383860409424946494228631669542910508020181"
+     "59266421349966065178030950759130587198464239060686371020051087232827846788436319445158661350412234790147923695852"
+     "08321597621066375401613736583044193603714778355306682834535634005074073040135602968046375918583163124224521599262"
+     "54649430083685186171942241764645513713542013221703137049658321015465406803539741790602258950302350193751977303094"
+     "57631732108525072993050897615825191597207572324554347709124613174935802817344665527343750000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000001e-308",
+        chars_format::scientific, 1774, errc{}, 0x0.fffffffffffffp-1022},
+
+    // above (0 + 1 - 2 * 2^-53) * 2^-1022: appended a 1 digit
+    {"2."
+     "22507385850720088902458687608585988765042311224095946549352480256244000922823569517877588880375915526423097809504"
+     "34312085877387158357291821993020294379224223559819827501242041788969571311791082261043971979604000454897391938079"
+     "19893608152561311337614984204327175103362739154978273159414382813627511383860409424946494228631669542910508020181"
+     "59266421349966065178030950759130587198464239060686371020051087232827846788436319445158661350412234790147923695852"
+     "08321597621066375401613736583044193603714778355306682834535634005074073040135602968046375918583163124224521599262"
+     "54649430083685186171942241764645513713542013221703137049658321015465406803539741790602258950302350193751977303094"
+     "57631732108525072993050897615825191597207572324554347709124613174935802817344665527343751e-308",
+        chars_format::scientific, 774, errc{}, 0x0.fffffffffffffp-1022},
+
+    // above (0 + 1 - 2 * 2^-53) * 2^-1022: incremented last digit
+    {"2."
+     "22507385850720088902458687608585988765042311224095946549352480256244000922823569517877588880375915526423097809504"
+     "34312085877387158357291821993020294379224223559819827501242041788969571311791082261043971979604000454897391938079"
+     "19893608152561311337614984204327175103362739154978273159414382813627511383860409424946494228631669542910508020181"
+     "59266421349966065178030950759130587198464239060686371020051087232827846788436319445158661350412234790147923695852"
+     "08321597621066375401613736583044193603714778355306682834535634005074073040135602968046375918583163124224521599262"
+     "54649430083685186171942241764645513713542013221703137049658321015465406803539741790602258950302350193751977303094"
+     "5763173210852507299305089761582519159720757232455434770912461317493580281734466552734376e-308",
+        chars_format::scientific, 773, errc{}, 0x0.fffffffffffffp-1022},
+
+    // below (0 + 1 - 2^-53) * 2^-1022: decremented last digit, then appended three 9 digits
+    {"2."
+     "22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508791414915891303"
+     "96211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072"
+     "85255133155755015914397476397983411801999323962548289017107081850690630666655994938275772572015763062690663332647"
+     "56530000924588831643303777979186961204949739037782970490505108060994073026293712895895000358379996720725430436028"
+     "40788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215"
+     "03775666622503982534335974568884423900265498198385487948292206894721689831099698365846814022854243330660339850886"
+     "44580400103493397042756718644338377048603786162277173854562306587467901408672332763671874999e-308",
+        chars_format::scientific, 777, errc{}, 0x0.fffffffffffffp-1022},
+
+    // (0 + 1 - 2^-53) * 2^-1022 exactly
+    {"2."
+     "22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508791414915891303"
+     "96211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072"
+     "85255133155755015914397476397983411801999323962548289017107081850690630666655994938275772572015763062690663332647"
+     "56530000924588831643303777979186961204949739037782970490505108060994073026293712895895000358379996720725430436028"
+     "40788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215"
+     "03775666622503982534335974568884423900265498198385487948292206894721689831099698365846814022854243330660339850886"
+     "44580400103493397042756718644338377048603786162277173854562306587467901408672332763671875e-308",
+        chars_format::scientific, 774, errc{}, 0x1.0000000000000p-1022},
+
+    // (0 + 1 - 2^-53) * 2^-1022 exactly, followed by a thousand 0 digits
+    {"2."
+     "22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508791414915891303"
+     "96211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072"
+     "85255133155755015914397476397983411801999323962548289017107081850690630666655994938275772572015763062690663332647"
+     "56530000924588831643303777979186961204949739037782970490505108060994073026293712895895000358379996720725430436028"
+     "40788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215"
+     "03775666622503982534335974568884423900265498198385487948292206894721689831099698365846814022854243330660339850886"
+     "44580400103493397042756718644338377048603786162277173854562306587467901408672332763671875000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000000e-308",
+        chars_format::scientific, 1774, errc{}, 0x1.0000000000000p-1022},
+
+    // above (0 + 1 - 2^-53) * 2^-1022: append a thousand 0 digits followed by a 1 digit
+    {"2."
+     "22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508791414915891303"
+     "96211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072"
+     "85255133155755015914397476397983411801999323962548289017107081850690630666655994938275772572015763062690663332647"
+     "56530000924588831643303777979186961204949739037782970490505108060994073026293712895895000358379996720725430436028"
+     "40788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215"
+     "03775666622503982534335974568884423900265498198385487948292206894721689831099698365846814022854243330660339850886"
+     "44580400103493397042756718644338377048603786162277173854562306587467901408672332763671875000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000001e-308",
+        chars_format::scientific, 1775, errc{}, 0x1.0000000000000p-1022},
+
+    // above (0 + 1 - 2^-53) * 2^-1022: appended a 1 digit
+    {"2."
+     "22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508791414915891303"
+     "96211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072"
+     "85255133155755015914397476397983411801999323962548289017107081850690630666655994938275772572015763062690663332647"
+     "56530000924588831643303777979186961204949739037782970490505108060994073026293712895895000358379996720725430436028"
+     "40788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215"
+     "03775666622503982534335974568884423900265498198385487948292206894721689831099698365846814022854243330660339850886"
+     "445804001034933970427567186443383770486037861622771738545623065874679014086723327636718751e-308",
+        chars_format::scientific, 775, errc{}, 0x1.0000000000000p-1022},
+
+    // above (0 + 1 - 2^-53) * 2^-1022: incremented last digit
+    {"2."
+     "22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508791414915891303"
+     "96211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072"
+     "85255133155755015914397476397983411801999323962548289017107081850690630666655994938275772572015763062690663332647"
+     "56530000924588831643303777979186961204949739037782970490505108060994073026293712895895000358379996720725430436028"
+     "40788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215"
+     "03775666622503982534335974568884423900265498198385487948292206894721689831099698365846814022854243330660339850886"
+     "44580400103493397042756718644338377048603786162277173854562306587467901408672332763671876e-308",
+        chars_format::scientific, 774, errc{}, 0x1.0000000000000p-1022},
+
+    // below (0 + 1 - 0.5 * 2^-53) * 2^-1022: decremented last digit, then appended three 9 digits
+    {"2."
+     "22507385850720125957382125702076802007701776340698873928837676330601332841749757068540634146032305423910824932203"
+     "77160560112603001240273771918347963927697214370789908365327989044318498647325041104672730846969778120287162365569"
+     "67935895657351868202788722494811530151317616366333296945953431369222190308053787694940411743707809822580740988880"
+     "55161790711900214875940191589215148208192489026331270225732118475077186145222409621263169862363877686014183806116"
+     "57022637766409076481944355360543363737279780145931006786604921175167849085215111597673733233391919832213268535191"
+     "28338784891913380715532840971003878993627240686726663397609149834349831344879676653469091559130189899114521124782"
+     "380547341009775590676096291585949697743018930811385869272811532937339507043361663818359374999e-308",
+        chars_format::scientific, 778, errc{}, 0x1.0000000000000p-1022},
+
+    // (0 + 1 - 0.5 * 2^-53) * 2^-1022 exactly
+    {"2."
+     "22507385850720125957382125702076802007701776340698873928837676330601332841749757068540634146032305423910824932203"
+     "77160560112603001240273771918347963927697214370789908365327989044318498647325041104672730846969778120287162365569"
+     "67935895657351868202788722494811530151317616366333296945953431369222190308053787694940411743707809822580740988880"
+     "55161790711900214875940191589215148208192489026331270225732118475077186145222409621263169862363877686014183806116"
+     "57022637766409076481944355360543363737279780145931006786604921175167849085215111597673733233391919832213268535191"
+     "28338784891913380715532840971003878993627240686726663397609149834349831344879676653469091559130189899114521124782"
+     "380547341009775590676096291585949697743018930811385869272811532937339507043361663818359375e-308",
+        chars_format::scientific, 775, errc{}, 0x1.0000000000000p-1022},
+
+    // (0 + 1 - 0.5 * 2^-53) * 2^-1022 exactly, followed by a thousand 0 digits
+    {"2."
+     "22507385850720125957382125702076802007701776340698873928837676330601332841749757068540634146032305423910824932203"
+     "77160560112603001240273771918347963927697214370789908365327989044318498647325041104672730846969778120287162365569"
+     "67935895657351868202788722494811530151317616366333296945953431369222190308053787694940411743707809822580740988880"
+     "55161790711900214875940191589215148208192489026331270225732118475077186145222409621263169862363877686014183806116"
+     "57022637766409076481944355360543363737279780145931006786604921175167849085215111597673733233391919832213268535191"
+     "28338784891913380715532840971003878993627240686726663397609149834349831344879676653469091559130189899114521124782"
+     "38054734100977559067609629158594969774301893081138586927281153293733950704336166381835937500000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000e-308",
+        chars_format::scientific, 1775, errc{}, 0x1.0000000000000p-1022},
+
+    // above (0 + 1 - 0.5 * 2^-53) * 2^-1022: append a thousand 0 digits followed by a 1 digit
+    {"2."
+     "22507385850720125957382125702076802007701776340698873928837676330601332841749757068540634146032305423910824932203"
+     "77160560112603001240273771918347963927697214370789908365327989044318498647325041104672730846969778120287162365569"
+     "67935895657351868202788722494811530151317616366333296945953431369222190308053787694940411743707809822580740988880"
+     "55161790711900214875940191589215148208192489026331270225732118475077186145222409621263169862363877686014183806116"
+     "57022637766409076481944355360543363737279780145931006786604921175167849085215111597673733233391919832213268535191"
+     "28338784891913380715532840971003878993627240686726663397609149834349831344879676653469091559130189899114521124782"
+     "38054734100977559067609629158594969774301893081138586927281153293733950704336166381835937500000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000001e-308",
+        chars_format::scientific, 1776, errc{}, 0x1.0000000000000p-1022},
+
+    // above (0 + 1 - 0.5 * 2^-53) * 2^-1022: appended a 1 digit
+    {"2."
+     "22507385850720125957382125702076802007701776340698873928837676330601332841749757068540634146032305423910824932203"
+     "77160560112603001240273771918347963927697214370789908365327989044318498647325041104672730846969778120287162365569"
+     "67935895657351868202788722494811530151317616366333296945953431369222190308053787694940411743707809822580740988880"
+     "55161790711900214875940191589215148208192489026331270225732118475077186145222409621263169862363877686014183806116"
+     "57022637766409076481944355360543363737279780145931006786604921175167849085215111597673733233391919832213268535191"
+     "28338784891913380715532840971003878993627240686726663397609149834349831344879676653469091559130189899114521124782"
+     "3805473410097755906760962915859496977430189308113858692728115329373395070433616638183593751e-308",
+        chars_format::scientific, 776, errc{}, 0x1.0000000000000p-1022},
+
+    // above (0 + 1 - 0.5 * 2^-53) * 2^-1022: incremented last digit
+    {"2."
+     "22507385850720125957382125702076802007701776340698873928837676330601332841749757068540634146032305423910824932203"
+     "77160560112603001240273771918347963927697214370789908365327989044318498647325041104672730846969778120287162365569"
+     "67935895657351868202788722494811530151317616366333296945953431369222190308053787694940411743707809822580740988880"
+     "55161790711900214875940191589215148208192489026331270225732118475077186145222409621263169862363877686014183806116"
+     "57022637766409076481944355360543363737279780145931006786604921175167849085215111597673733233391919832213268535191"
+     "28338784891913380715532840971003878993627240686726663397609149834349831344879676653469091559130189899114521124782"
+     "380547341009775590676096291585949697743018930811385869272811532937339507043361663818359376e-308",
+        chars_format::scientific, 775, errc{}, 0x1.0000000000000p-1022},
+
+    // below 1 * 2^-1022: decremented last digit, then appended three 9 digits
+    {"2."
+     "22507385850720138309023271733240406421921598046233183055332741688720443481391819585428315901251102056406733973103"
+     "58110051524341615534601088560123853777188211307779935320023304796101474425836360719215650469425037342083752508066"
+     "50616658158948720491179968591639648500635908770118304874799780887753749949451580451605050915399856582470818645113"
+     "53793580499211598108576605199243335211435239014879569960959128889160299264151106346631339366347758651302937176204"
+     "73256317814856643508721228286376420448468114076139114770628016898532441100241614474216185671661505401542850847167"
+     "52901903161322778896729707373123334086988983175067838846926092773977972858659654941091369095406136467568702398678"
+     "315290680984617210924625396728515624999e-308",
+        chars_format::scientific, 724, errc{}, 0x1.0000000000000p-1022},
+
+    // 1 * 2^-1022 exactly
+    {"2."
+     "22507385850720138309023271733240406421921598046233183055332741688720443481391819585428315901251102056406733973103"
+     "58110051524341615534601088560123853777188211307779935320023304796101474425836360719215650469425037342083752508066"
+     "50616658158948720491179968591639648500635908770118304874799780887753749949451580451605050915399856582470818645113"
+     "53793580499211598108576605199243335211435239014879569960959128889160299264151106346631339366347758651302937176204"
+     "73256317814856643508721228286376420448468114076139114770628016898532441100241614474216185671661505401542850847167"
+     "52901903161322778896729707373123334086988983175067838846926092773977972858659654941091369095406136467568702398678"
+     "315290680984617210924625396728515625e-308",
+        chars_format::scientific, 721, errc{}, 0x1.0000000000000p-1022},
+
+    // (1 + 1 - 2 * 2^-53) * 2^1023 exactly
+    {"17976931348623157081452742373170435679807056752584499659891747680315726078002853876058955863276687817154045895351"
+     "43824642343213268894641827684675467035375169860499105765512820762454900903893289440758685084551339423045832369032"
+     "22948165808559332123348274797826204144723168738177180919299881250404026184124858368",
+        chars_format::fixed, 309, errc{}, 0x1.fffffffffffffp+1023},
+
+    // (1 + 1 - 2 * 2^-53) * 2^1023 exactly, followed by a thousand 0 digits
+    {"17976931348623157081452742373170435679807056752584499659891747680315726078002853876058955863276687817154045895351"
+     "43824642343213268894641827684675467035375169860499105765512820762454900903893289440758685084551339423045832369032"
+     "22948165808559332123348274797826204144723168738177180919299881250404026184124858368."
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+        chars_format::fixed, 1310, errc{}, 0x1.fffffffffffffp+1023},
+
+    // above (1 + 1 - 2 * 2^-53) * 2^1023, appended a thousand 0 digits followed by a 1 digit
+    {"17976931348623157081452742373170435679807056752584499659891747680315726078002853876058955863276687817154045895351"
+     "43824642343213268894641827684675467035375169860499105765512820762454900903893289440758685084551339423045832369032"
+     "22948165808559332123348274797826204144723168738177180919299881250404026184124858368."
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001",
+        chars_format::fixed, 1311, errc{}, 0x1.fffffffffffffp+1023},
+
+    // above (1 + 1 - 2 * 2^-53) * 2^1023: appended a 1 digit
+    {"17976931348623157081452742373170435679807056752584499659891747680315726078002853876058955863276687817154045895351"
+     "43824642343213268894641827684675467035375169860499105765512820762454900903893289440758685084551339423045832369032"
+     "22948165808559332123348274797826204144723168738177180919299881250404026184124858368.1",
+        chars_format::fixed, 311, errc{}, 0x1.fffffffffffffp+1023},
+
+    // above (1 + 1 - 2 * 2^-53) * 2^1023: incremented last digit
+    {"17976931348623157081452742373170435679807056752584499659891747680315726078002853876058955863276687817154045895351"
+     "43824642343213268894641827684675467035375169860499105765512820762454900903893289440758685084551339423045832369032"
+     "22948165808559332123348274797826204144723168738177180919299881250404026184124858369",
+        chars_format::fixed, 309, errc{}, 0x1.fffffffffffffp+1023},
+
+    // below (1 + 1 - 2^-53) * 2^1023: decremented last digit, then appended three 9 digits
+    {"17976931348623158079372897140530341507993413271003782693617377898044496829276475094664901797758720709633028641669"
+     "28879109465555478519404026306574886715058206819089020007083836762738548458177115317644757302700698555713669596228"
+     "42914819860834936475292719074168444365510704342711559699508093042880177904174497791.999",
+        chars_format::fixed, 313, errc{}, 0x1.fffffffffffffp+1023},
+
+    // (1 + 1 - 2^-53) * 2^1023 exactly
+    {"17976931348623158079372897140530341507993413271003782693617377898044496829276475094664901797758720709633028641669"
+     "28879109465555478519404026306574886715058206819089020007083836762738548458177115317644757302700698555713669596228"
+     "42914819860834936475292719074168444365510704342711559699508093042880177904174497792",
+        chars_format::fixed, 309, errc::result_out_of_range, double_inf},
+
+    // (1 + 1 - 2^-53) * 2^1023 exactly, followed by a thousand 0 digits
+    {"17976931348623158079372897140530341507993413271003782693617377898044496829276475094664901797758720709633028641669"
+     "28879109465555478519404026306574886715058206819089020007083836762738548458177115317644757302700698555713669596228"
+     "42914819860834936475292719074168444365510704342711559699508093042880177904174497792."
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+        chars_format::fixed, 1310, errc::result_out_of_range, double_inf},
+
+    // above (1 + 1 - 2^-53) * 2^1023: append a thousand 0 digits followed by a 1 digit
+    {"17976931348623158079372897140530341507993413271003782693617377898044496829276475094664901797758720709633028641669"
+     "28879109465555478519404026306574886715058206819089020007083836762738548458177115317644757302700698555713669596228"
+     "42914819860834936475292719074168444365510704342711559699508093042880177904174497792."
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+     "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001",
+        chars_format::fixed, 1311, errc::result_out_of_range, double_inf},
+
+    // above (1 + 1 - 2^-53) * 2^1023: appended a 1 digit
+    {"17976931348623158079372897140530341507993413271003782693617377898044496829276475094664901797758720709633028641669"
+     "28879109465555478519404026306574886715058206819089020007083836762738548458177115317644757302700698555713669596228"
+     "42914819860834936475292719074168444365510704342711559699508093042880177904174497792.1",
+        chars_format::fixed, 311, errc::result_out_of_range, double_inf},
+
+    // above (1 + 1 - 2^-53) * 2^1023: incremented last digit
+    {"17976931348623158079372897140530341507993413271003782693617377898044496829276475094664901797758720709633028641669"
+     "28879109465555478519404026306574886715058206819089020007083836762738548458177115317644757302700698555713669596228"
+     "42914819860834936475292719074168444365510704342711559699508093042880177904174497792",
+        chars_format::fixed, 309, errc::result_out_of_range, double_inf},
+
+    // below 1 * 2^1024: decremented last digit, then appended three 9 digits
+    {"17976931348623159077293051907890247336179769789423065727343008115773267580550096313270847732240753602112011387987"
+     "13933576587897688144166224928474306394741243777678934248654852763022196012460941194530829520850057688381506823424"
+     "62881473913110540827237163350510684586298239947245938479716304835356329624224137215.999",
+        chars_format::fixed, 313, errc::result_out_of_range, double_inf},
+
+    // 1 * 2^1024 exactly
+    {"17976931348623159077293051907890247336179769789423065727343008115773267580550096313270847732240753602112011387987"
+     "13933576587897688144166224928474306394741243777678934248654852763022196012460941194530829520850057688381506823424"
+     "62881473913110540827237163350510684586298239947245938479716304835356329624224137216",
+        chars_format::fixed, 309, errc::result_out_of_range, double_inf},
+};
+
+int
+main()
+{
+  for (const auto [input,fmt,correct_end,correct_ec,correct_value]
+       : double_from_chars_test_cases)
+    {
+      if (fmt == chars_format::hex)
+	// FIXME: Due to quirks in some strtod implementations, the hex
+	// testcases are currently disabled until we implement hex parsing in a
+	// more portable way that doesn't go through the target libc's strtod.
+	continue;
+
+      double value = -1.2345;
+      const auto [ptr,ec] = from_chars(input, input + strlen(input), value, fmt);
+      VERIFY( correct_ec == ec );
+      VERIFY( ptr == input + correct_end );
+      if (ec == errc{})
+	VERIFY( value == correct_value );
+      else
+	VERIFY( value == -1.2345 );
+    }
+}
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/float.cc b/libstdc++-v3/testsuite/20_util/from_chars/float.cc
new file mode 100644
index 00000000000..ba39b7e16a1
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/from_chars/float.cc
@@ -0,0 +1,296 @@
+// This file consists of testcases extracted from the MSVC STL testsuite.
+
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// { dg-do run { target c++17 } }
+// { dg-require-effective-target ieee-floats }
+
+#include <charconv>
+
+#include <limits>
+#include <cstring>
+#include <testsuite_hooks.h>
+
+using namespace std;
+
+inline constexpr float float_inf = numeric_limits<float>::infinity();
+
+struct float_to_chars_testcase {
+    const char* input;
+    chars_format fmt;
+    size_t correct_idx;
+    errc correct_ec;
+    float correct_value;
+};
+
+inline constexpr float_to_chars_testcase float_from_chars_test_cases[] = {
+    {"1.a0000400", chars_format::hex, 10, errc{}, 0x1.a00004p0f}, // exact
+    {"1.a0000401", chars_format::hex, 10, errc{}, 0x1.a00004p0f}, // below midpoint, round down
+    {"1.a0000500", chars_format::hex, 10, errc{}, 0x1.a00004p0f}, // midpoint, round down to even
+    {"1.a0000501", chars_format::hex, 10, errc{}, 0x1.a00006p0f}, // above midpoint, round up
+    {"1.a0000600", chars_format::hex, 10, errc{}, 0x1.a00006p0f}, // exact
+    {"1.a0000601", chars_format::hex, 10, errc{}, 0x1.a00006p0f}, // below midpoint, round down
+    {"1.a0000700", chars_format::hex, 10, errc{}, 0x1.a00008p0f}, // midpoint, round up to even
+    {"1.a0000701", chars_format::hex, 10, errc{}, 0x1.a00008p0f}, // above midpoint, round up
+
+    {"1.0000040", chars_format::hex, 9, errc{}, 0x1.000004p0f}, // exact
+    {"1.0000041", chars_format::hex, 9, errc{}, 0x1.000004p0f}, // below midpoint, round down
+    {"1.0000050", chars_format::hex, 9, errc{}, 0x1.000004p0f}, // midpoint, round down to even
+    {"1.0000051", chars_format::hex, 9, errc{}, 0x1.000006p0f}, // above midpoint, round up
+    {"1.0000060", chars_format::hex, 9, errc{}, 0x1.000006p0f}, // exact
+    {"1.0000061", chars_format::hex, 9, errc{}, 0x1.000006p0f}, // below midpoint, round down
+    {"1.0000070", chars_format::hex, 9, errc{}, 0x1.000008p0f}, // midpoint, round up to even
+    {"1.0000071", chars_format::hex, 9, errc{}, 0x1.000008p0f}, // above midpoint, round up
+
+    {"1.0000002384185791015625000000", chars_format::general, 30, errc{}, 0x1.000004p0f}, // exact
+    {"1.0000002421438694000244140625", chars_format::general, 30, errc{}, 0x1.000004p0f}, // below midpoint, round down
+    {"1.0000002980232238769531249999", chars_format::general, 30, errc{}, 0x1.000004p0f}, // below midpoint, round down
+    {"1.0000002980232238769531250000", chars_format::general, 30, errc{},
+        0x1.000004p0f}, // midpoint, round down to even
+    {"1.0000002980232238769531250001", chars_format::general, 30, errc{}, 0x1.000006p0f}, // above midpoint, round up
+    {"1.0000003017485141754150390625", chars_format::general, 30, errc{}, 0x1.000006p0f}, // above midpoint, round up
+    {"1.0000003576278686523437500000", chars_format::general, 30, errc{}, 0x1.000006p0f}, // exact
+    {"1.0000003613531589508056640625", chars_format::general, 30, errc{}, 0x1.000006p0f}, // below midpoint, round down
+    {"1.0000004172325134277343749999", chars_format::general, 30, errc{}, 0x1.000006p0f}, // below midpoint, round down
+    {"1.0000004172325134277343750000", chars_format::general, 30, errc{}, 0x1.000008p0f}, // midpoint, round up to even
+    {"1.0000004172325134277343750001", chars_format::general, 30, errc{}, 0x1.000008p0f}, // above midpoint, round up
+    {"1.0000004209578037261962890625", chars_format::general, 30, errc{}, 0x1.000008p0f}, // above midpoint, round up
+
+    // VSO-838635 "<charconv>: from_chars() mishandles certain subnormals"
+    // This bug didn't actually affect float, but we should have similar test cases.
+    // These values change on half-ulp boundaries:
+    // 1 * 2^-150 ~= 7.01e-46 (half-ulp between zero and min subnormal)
+    // 2 * 2^-150 ~= 1.40e-45 (min subnormal)
+    // 3 * 2^-150 ~= 2.10e-45 (half-ulp between min subnormal and next subnormal)
+    // 4 * 2^-150 ~= 2.80e-45 (next subnormal)
+    {"6."
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666"
+     "6666666666666666666e-46",
+        chars_format::scientific, 1006, errc::result_out_of_range, 0x0.000000p+0f},
+    {"7."
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777"
+     "7777777777777777777e-46",
+        chars_format::scientific, 1006, errc{}, 0x0.000002p-126f},
+    {"8."
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888"
+     "8888888888888888888e-46",
+        chars_format::scientific, 1006, errc{}, 0x0.000002p-126f},
+    {"9."
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"
+     "9999999999999999999e-46",
+        chars_format::scientific, 1006, errc{}, 0x0.000002p-126f},
+    {"1."
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111"
+     "1111111111111111111e-45",
+        chars_format::scientific, 1006, errc{}, 0x0.000002p-126f},
+    {"2."
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+     "2222222222222222222e-45",
+        chars_format::scientific, 1006, errc{}, 0x0.000004p-126f},
+
+    // VSO-733765 "<charconv>: [Feedback] double std::from_chars behavior on exponent out of range"
+    // LWG-3081 "Floating point from_chars API does not distinguish between overflow and underflow"
+    // These test cases exercise every overflow/underflow codepath.
+    {"1e+1000", chars_format::scientific, 7, errc::result_out_of_range, float_inf},
+    {"1e-1000", chars_format::scientific, 7, errc::result_out_of_range, 0.0f},
+    {"1.ffffffp+127", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+    {"1e+2000", chars_format::scientific, 7, errc::result_out_of_range, float_inf},
+    {"1e-2000", chars_format::scientific, 7, errc::result_out_of_range, 0.0f},
+    {"1e+9999", chars_format::scientific, 7, errc::result_out_of_range, float_inf},
+    {"1e-9999", chars_format::scientific, 7, errc::result_out_of_range, 0.0f},
+    {"10e+5199", chars_format::scientific, 8, errc::result_out_of_range, float_inf},
+    {"0.001e-5199", chars_format::scientific, 11, errc::result_out_of_range, 0.0f},
+
+    // GH-931 "<charconv>: hex from_chars(\"0.fffffffffffff8p-1022\") is incorrect"
+    // Test cases for values close to std::numeric_limits<float>::min() and std::numeric_limits<float>::max()
+    {"7.fffffp-129", chars_format::hex, 12, errc{}, 0x0.fffffep-126f},
+    {"8.00000p-129", chars_format::hex, 12, errc{}, 0x1.000000p-126f},
+
+    {"0.fffffep-126", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"0.ffffffp-126", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"1.000000p-126", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+
+    {"1.fffffcp-127", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"1.fffffdp-127", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"1.fffffep-127", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"1.ffffffp-127", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"2.000000p-127", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+
+    {"3.fffff8p-128", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"3.fffff9p-128", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"3.fffffbp-128", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"3.fffffcp-128", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"3.fffffdp-128", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"3.fffffep-128", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"3.ffffffp-128", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"4.000000p-128", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+
+    {"7.fffff0p-129", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"7.fffff1p-129", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"7.fffff7p-129", chars_format::hex, 13, errc{}, 0x0.fffffep-126f},
+    {"7.fffff8p-129", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"7.fffff9p-129", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"7.fffffbp-129", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"7.fffffcp-129", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"7.fffffdp-129", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"7.ffffffp-129", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+    {"8.000000p-129", chars_format::hex, 13, errc{}, 0x1.000000p-126f},
+
+    {"0.fffffe0p-126", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"0.fffffe1p-126", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"0.fffffefp-126", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"0.ffffff0p-126", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"0.ffffff1p-126", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"0.ffffff7p-126", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"0.ffffff8p-126", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"0.ffffff9p-126", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"0.fffffffp-126", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"1.0000000p-126", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+
+    {"1.fffffc0p-127", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"1.fffffc1p-127", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"1.fffffdfp-127", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"1.fffffe0p-127", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"1.fffffe1p-127", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"1.fffffefp-127", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"1.ffffff0p-127", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"1.ffffff1p-127", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"1.fffffffp-127", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"2.0000000p-127", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+
+    {"3.fffff80p-128", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"3.fffff81p-128", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"3.fffffbfp-128", chars_format::hex, 14, errc{}, 0x0.fffffep-126f},
+    {"3.fffffc0p-128", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"3.fffffc1p-128", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"3.fffffdfp-128", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"3.fffffe0p-128", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"3.fffffe1p-128", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"3.fffffffp-128", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+    {"4.0000000p-128", chars_format::hex, 14, errc{}, 0x1.000000p-126f},
+
+    {"0.ffffffp+128", chars_format::hex, 13, errc{}, 0x1.fffffep+127f},
+    {"1.000000p+128", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+
+    {"1.fffffep+127", chars_format::hex, 13, errc{}, 0x1.fffffep+127f},
+    {"1.ffffffp+127", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+    {"2.000000p+127", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+
+    {"3.fffffcp+126", chars_format::hex, 13, errc{}, 0x1.fffffep+127f},
+    {"3.fffffdp+126", chars_format::hex, 13, errc{}, 0x1.fffffep+127f},
+    {"3.fffffep+126", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+    {"3.ffffffp+126", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+    {"4.000000p+126", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+
+    {"7.fffff8p+125", chars_format::hex, 13, errc{}, 0x1.fffffep+127f},
+    {"7.fffff9p+125", chars_format::hex, 13, errc{}, 0x1.fffffep+127f},
+    {"7.fffffbp+125", chars_format::hex, 13, errc{}, 0x1.fffffep+127f},
+    {"7.fffffcp+125", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+    {"7.fffffdp+125", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+    {"7.ffffffp+125", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+    {"8.000000p+125", chars_format::hex, 13, errc::result_out_of_range, float_inf},
+
+    {"0.ffffff0p+128", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"0.ffffff1p+128", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"0.ffffff7p+128", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"0.ffffff8p+128", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"0.ffffff9p+128", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"0.fffffffp+128", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"1.0000000p+128", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+
+    {"1.fffffe0p+127", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"1.fffffe1p+127", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"1.fffffefp+127", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"1.ffffff0p+127", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"1.ffffff1p+127", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"1.fffffffp+127", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"2.0000000p+127", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+
+    {"3.fffffc0p+126", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"3.fffffc1p+126", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"3.fffffdfp+126", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"3.fffffe0p+126", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"3.fffffe1p+126", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"3.fffffffp+126", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"4.0000000p+126", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+
+    {"7.fffff80p+125", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"7.fffff81p+125", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"7.fffffbfp+125", chars_format::hex, 14, errc{}, 0x1.fffffep+127f},
+    {"7.fffffc0p+125", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"7.fffffc1p+125", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"7.fffffffp+125", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+    {"8.0000000p+125", chars_format::hex, 14, errc::result_out_of_range, float_inf},
+};
+
+int
+main()
+{
+  for (const auto [input,fmt,correct_end,correct_ec,correct_value]
+       : float_from_chars_test_cases)
+    {
+      if (fmt == chars_format::hex)
+	// FIXME: Due to quirks in some strtod implementations, the hex
+	// testcases are currently disabled until we implement hex parsing in a
+	// more portable way that doesn't go through the target libc's strtod.
+	continue;
+
+      float value = -1.2345f;
+      const auto [ptr,ec] = from_chars(input, input + strlen(input), value, fmt);
+      VERIFY( correct_ec == ec );
+      VERIFY( ptr == input + correct_end );
+      if (ec == errc{})
+	VERIFY( value == correct_value );
+      else
+	VERIFY( value == -1.2345f );
+    }
+}
