Add C++ versions of iscanonical for ldbl-96 and ldbl-128ibm

diff --git a/math/Makefile b/math/Makefile
index 6c8aa3e413..008eeb2d18 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -208,7 +208,8 @@  tests-internal = test-matherr test-matherr-2
 tests-static += atest-exp atest-sincos atest-exp2
 
 ifneq (,$(CXX))
-tests += test-math-isinff test-math-iszero test-math-issignaling
+tests += test-math-isinff test-math-iszero test-math-issignaling \
+	 test-math-iscanonical
 endif
 
 ifneq (no,$(PERL))
@@ -356,6 +357,7 @@  CFLAGS-test-signgam-ullong-init-static.c = -std=c99
 CFLAGS-test-math-isinff.cc = -std=gnu++11
 CFLAGS-test-math-iszero.cc = -std=gnu++11
 CFLAGS-test-math-issignaling.cc = -std=gnu++11
+CFLAGS-test-math-iscanonical.cc = -std=gnu++11
 
 CFLAGS-test-iszero-excess-precision.c = -fexcess-precision=standard
 CFLAGS-test-iseqsig-excess-precision.c = -fexcess-precision=standard
diff --git a/math/test-math-iscanonical.cc b/math/test-math-iscanonical.cc
new file mode 100644
index 0000000000..aba68acb4f
--- /dev/null
+++ b/math/test-math-iscanonical.cc
@@ -0,0 +1,48 @@ 
+/* Test for the C++ implementation of iscanonical.
+   Copyright (C) 2017 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/>.  */
+
+#define _GNU_SOURCE 1
+#include <math.h>
+#include <stdio.h>
+
+static bool errors;
+
+template <class T>
+static void
+check_type ()
+{
+  T val = 0;
+
+  /* Check if iscanonical is available in C++ mode (bug 22235).  */
+  if (iscanonical (val) == 0)
+    errors++;
+}
+
+static int
+do_test (void)
+{
+  check_type<float> ();
+  check_type<double> ();
+  check_type<long double> ();
+#if __HAVE_DISTINCT_FLOAT128
+  check_type<_Float128> ();
+#endif
+  return errors;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h b/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h
index 7ddb368d26..1741aac048 100644
--- a/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h
+++ b/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h
@@ -37,5 +37,22 @@  extern int __iscanonicall (long double __x)
    conversion, before being discarded; in IBM long double, there are
    encodings that are not consistently handled as corresponding to any
    particular value of the type, and we return 0 for those.  */
-# define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
-#endif
+# ifndef __cplusplus
+#  define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
+# else
+/* In C++ mode, __MATH_TG cannot be used, because it relies on
+   __builtin_types_compatible_p, which is a C-only builtin.  On the
+   other hand, overloading provides the means to distinguish between
+   the floating-point types.  The overloading resolution will match
+   the correct parameter (regardless of type qualifiers (i.e.: const
+   and volatile).  */
+extern "C++" {
+inline int iscanonical (float __val) { return __iscanonicalf (__val); }
+inline int iscanonical (double __val) { return __iscanonical (__val); }
+inline int iscanonical (long double __val) { return __iscanonicall (__val); }
+#  if __HAVE_DISTINCT_FLOAT128
+inline int iscanonical (_Float128 __val) { return __iscanonicalf128 (__val); }
+#  endif
+}
+# endif /* __cplusplus */
+#endif /* __NO_LONG_DOUBLE_MATH */
diff --git a/sysdeps/ieee754/ldbl-96/bits/iscanonical.h b/sysdeps/ieee754/ldbl-96/bits/iscanonical.h
index 4a4f4ad024..366125a2cc 100644
--- a/sysdeps/ieee754/ldbl-96/bits/iscanonical.h
+++ b/sysdeps/ieee754/ldbl-96/bits/iscanonical.h
@@ -34,4 +34,21 @@  extern int __iscanonicall (long double __x)
    conversion, before being discarded; in extended precision, there
    are encodings that are not consistently handled as corresponding to
    any particular value of the type, and we return 0 for those.  */
-#define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
+#ifndef __cplusplus
+# define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
+#else
+/* In C++ mode, __MATH_TG cannot be used, because it relies on
+   __builtin_types_compatible_p, which is a C-only builtin.  On the
+   other hand, overloading provides the means to distinguish between
+   the floating-point types.  The overloading resolution will match
+   the correct parameter (regardless of type qualifiers (i.e.: const
+   and volatile).  */
+extern "C++" {
+inline int iscanonical (float __val) { return __iscanonicalf (__val); }
+inline int iscanonical (double __val) { return __iscanonical (__val); }
+inline int iscanonical (long double __val) { return __iscanonicall (__val); }
+# if __HAVE_DISTINCT_FLOAT128
+inline int iscanonical (_Float128 __val) { return __iscanonicalf128 (__val); }
+# endif
+}
+#endif /* __cplusplus */
diff --git a/sysdeps/powerpc/powerpc64le/Makefile b/sysdeps/powerpc/powerpc64le/Makefile
index 3fd9d9a715..f554a791b7 100644
--- a/sysdeps/powerpc/powerpc64le/Makefile
+++ b/sysdeps/powerpc/powerpc64le/Makefile
@@ -16,6 +16,7 @@  $(foreach suf,$(all-object-suffixes),%f128_r$(suf)): CFLAGS += -mfloat128
 $(foreach suf,$(all-object-suffixes),$(objpfx)test-float128%$(suf)): CFLAGS += -mfloat128
 $(foreach suf,$(all-object-suffixes),$(objpfx)test-ifloat128%$(suf)): CFLAGS += -mfloat128
 CFLAGS-libm-test-support-float128.c += -mfloat128
+CFLAGS-test-math-iscanonical.cc += -mfloat128
 CFLAGS-test-math-issignaling.cc += -mfloat128
 CFLAGS-test-math-iszero.cc += -mfloat128
 $(objpfx)test-float128% $(objpfx)test-ifloat128% $(objpfx)test-math-iszero: \