[1/2] Fix behaviour of 'is_binary128' in __printf_fp
Commit Message
Should this have an associated bugzilla entry?
-- 8< --
Both 'is_long_double' and 'is_binary128' (members of the 'printf_info'
structure) are used in __printf_fp to select the type of the
floating-point argument it receives in its 'args' parameter. When the
argument is of double type, 'is_long_double' should be set to zero.
Similarly, when the argument is of long double type, 'is_long_double'
should be set to one. More recently (since the addition of the
_Float128 API), the floating-point argument can also be of _Float128
type, then 'is_binary128' should be set to one.
In current __printf_fp, when 'is_binary128' is one, the floating-point
argument is treated as if it was of _Float128 type, regardless of the
value of 'is_long_double'. This is not a problem for strfromd, because
strfromd always sets 'is_binary128' to zero. However, it could be a
problem for users of printf_size, who could be expecting that
'is_long_double == 0' meant that the 'args' parameter was of double
type, regardless of the value of 'is_binary128'.
This patch modifies this behaviour in __printf_fp and adjusts
strfromf128 so that it always sets 'is_long_double' to one.
Tested for powerpc64le and x86_64.
* stdio-common/printf_fp.c (__printf_fp_l): Also check the value
of 'is_long_double' before reading the argument into a variable
of _Float128 type.
* stdio-common/printf_size.c (__printf_size): Likewise.
* stdlib/strfrom-skeleton.c [__HAVE_DISTINCT_FLOAT128] (STRFROM):
If 'is_binary128' is one, also set 'is_long_double' to one.
* stdio-common/Makefile (test-srcs): Add tst-isbinary128
(tests-special) Add $(objpfx)tst-isbinary128.out.
($(objpfx)tst-isbinary128.out): New build and run rule.
* stdio-common/tst-isbinary128.c: New file.
* stdio-common/tst-isbinary128.sh: Likewise.
---
stdio-common/Makefile | 9 +++++--
stdio-common/printf_fp.c | 2 +-
stdio-common/printf_size.c | 2 +-
stdio-common/tst-isbinary128.c | 59 +++++++++++++++++++++++++++++++++++++++++
stdio-common/tst-isbinary128.sh | 38 ++++++++++++++++++++++++++
stdlib/strfrom-skeleton.c | 6 ++++-
6 files changed, 111 insertions(+), 5 deletions(-)
create mode 100644 stdio-common/tst-isbinary128.c
create mode 100644 stdio-common/tst-isbinary128.sh
Comments
On Fri, 29 Jun 2018, Gabriel F. T. Gomes wrote:
> Should this have an associated bugzilla entry?
>
> -- 8< --
> Both 'is_long_double' and 'is_binary128' (members of the 'printf_info'
> structure) are used in __printf_fp to select the type of the
> floating-point argument it receives in its 'args' parameter. When the
> argument is of double type, 'is_long_double' should be set to zero.
> Similarly, when the argument is of long double type, 'is_long_double'
> should be set to one. More recently (since the addition of the
> _Float128 API), the floating-point argument can also be of _Float128
> type, then 'is_binary128' should be set to one.
>
> In current __printf_fp, when 'is_binary128' is one, the floating-point
> argument is treated as if it was of _Float128 type, regardless of the
> value of 'is_long_double'. This is not a problem for strfromd, because
> strfromd always sets 'is_binary128' to zero. However, it could be a
> problem for users of printf_size, who could be expecting that
> 'is_long_double == 0' meant that the 'args' parameter was of double
> type, regardless of the value of 'is_binary128'.
Well, the main use case of printf_size is being registered as a printf
handler, not users creating their own printf_info structure. I'm not
convinced that calling printf_size with any form of printf_info structure
that cannot be created by printf functions is valid.
It's certainly true that adding support for float128 versions of printf
means a documentation patch is required to document is_binary128 in
stdio.texi. But why should the semantics be that is_long_double == 0
overrides is_binary128 rather than is_binary128 being independent of
is_long_double? I'd have expected the documentation to say that
is_binary128 is set alongside is_long_double in the case where printf has
the 'L' modifier and is called from code with binary128 long double, on a
platform where that's the third long double format supported by glibc,
i.e. powerpc64le, but that printf will never set is_binary128 without
is_long_double (and thus what printf_size does with that combination is
basically irrelevant, but I'd think it natural for it to make is_binary128
== 1 take precedence over is_long_double).
(So handlers could potentially, on powerpc64le, themselves deal with both
ibm128 and binary128 long double, but if not trying to do so - if the
handler is always built with the same long double format as the printf
caller - they could just ignore is_binary128.)
@@ -63,13 +63,14 @@ tests := tstscanf test_rdwr test-popen tstgetln test-fseek \
tst-vfprintf-mbs-prec \
tst-scanf-round \
-test-srcs = tst-unbputc tst-printf
+test-srcs = tst-unbputc tst-printf tst-isbinary128
ifeq ($(run-built-tests),yes)
tests-special += $(objpfx)tst-unbputc.out $(objpfx)tst-printf.out \
$(objpfx)tst-printf-bz18872-mem.out \
$(objpfx)tst-setvbuf1-cmp.out \
- $(objpfx)tst-vfprintf-width-prec-mem.out
+ $(objpfx)tst-vfprintf-width-prec-mem.out \
+ $(objpfx)tst-isbinary128.out
generated += tst-printf-bz18872.c tst-printf-bz18872.mtrace \
tst-printf-bz18872-mem.out \
tst-vfprintf-width-prec.mtrace tst-vfprintf-width-prec-mem.out
@@ -103,6 +104,10 @@ $(objpfx)tst-printf.out: tst-printf.sh $(objpfx)tst-printf
$(SHELL) $< $(common-objpfx) '$(test-program-prefix)' > $@; \
$(evaluate-test)
+$(objpfx)tst-isbinary128.out: tst-isbinary128.sh $(objpfx)tst-isbinary128
+ $(SHELL) $^ '$(test-program-prefix)' $@; \
+ $(evaluate-test)
+
# We generate this source because it requires a printf invocation with
# 10K arguments.
$(objpfx)tst-printf-bz18872.c: tst-printf-bz18872.sh
@@ -375,7 +375,7 @@ __printf_fp_l (FILE *fp, locale_t loc,
/* Fetch the argument value. */
#if __HAVE_DISTINCT_FLOAT128
- if (info->is_binary128)
+ if (info->is_binary128 && info->is_long_double)
PRINTF_FP_FETCH (_Float128, fpnum.f128, float128, FLT128_MANT_DIG)
else
#endif
@@ -142,7 +142,7 @@ __printf_size (FILE *fp, const struct printf_info *info,
/* Fetch the argument value. */
#if __HAVE_DISTINCT_FLOAT128
- if (info->is_binary128)
+ if (info->is_binary128 && info->is_long_double)
PRINTF_SIZE_FETCH (_Float128, fpnum.f128)
else
#endif
new file mode 100644
@@ -0,0 +1,59 @@
+/* Test for the behaviour of 'is_binary128' in printf_size.
+ Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <printf.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+ double d = 2000;
+ double *dptr = &d;
+ long double ld = 4000;
+ long double *ldptr = & ld;
+ struct printf_info info;
+
+ memset (&info, 0, sizeof (info));
+ info.spec = L'f';
+
+ /* First, call printf_size with 'is_long_double' and 'is_binary128'
+ both zeroed. */
+ printf_size (stdout, &info, (void *) &dptr);
+
+ /* Then test that setting 'is_binary128' to one still prints double
+ correctly. */
+ info.is_binary128 = 1;
+ printf_size (stdout, &info, (void *) &dptr);
+
+ /* Finally, check that long double values are also printed correctly,
+ provided that 'is_binary128' is zeroed. */
+ info.is_long_double = 1;
+ info.is_binary128 = 0;
+ printf_size (stdout, &info, (void *) &ldptr);
+
+ /* Setting both 'is_long_double' and 'is_binary128' to one is out of
+ the scope of this test, because such configuration is only valid
+ when _Float128 and long double are ABI-distinct (which is not
+ always true and this is an arch-independent test). */
+ return 0;
+}
+
+#include <support/test-driver.c>
new file mode 100644
@@ -0,0 +1,38 @@
+#!/bin/sh
+# Test for the behaviour of 'is_binary128' in printf_size.
+# Copyright (C) 2018 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# Lesser General Public License for more details.
+
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <http://www.gnu.org/licenses/>.
+
+set -e
+
+test_program=$1; shift
+test_program_prefix=$1; shift
+test_program_output=$1; shift
+
+status=0
+
+${test_program_prefix} \
+ ${test_program} \
+ > ${test_program_output} || status=1
+
+echo -n "2k2k4k" | cmp - ${test_program_output} > /dev/null 2>&1 ||
+{
+ status=1
+ echo "*** output comparison failed"
+}
+
+exit $status
@@ -133,9 +133,13 @@ STRFROM (char *dest, size_t size, const char *format, FLOAT f)
info.is_long_double = __builtin_types_compatible_p (FLOAT, long double);
/* Similarly, the function strfromf128 passes a floating-point number in
- _Float128 format to printf_fp. */
+ _Float128 format to __printf_fp. Setting is_binary128 alone is not
+ enough, because when is_long_double is zero, __printf_fp always treats
+ the floating-point number as double (regardless of is_binary128). */
#if __HAVE_DISTINCT_FLOAT128
info.is_binary128 = __builtin_types_compatible_p (FLOAT, _Float128);
+ if (info.is_binary128)
+ info.is_long_double = 1;
#endif
/* Set info according to the format string. */