Add C++ versions of iscanonical for ldbl-96 and ldbl-128ibm (bug 22235)

All representations of floating-point numbers in types with IEC 60559
binary exchange format are canonical.  On the other hand, types with IEC
60559 extended formats, such as those implemented under ldbl-96 and
ldbl-128ibm, contain representations that are not canonical.

TS 18661-1 introduced the type-generic macro iscanonical, which returns
whether a floating-point value is canonical or not.  In Glibc, this
type-generic macro is implemented using the macro __MATH_TG, which, when
support for float128 is enabled, relies on __builtin_types_compatible_p
to select between floating-point types.  However, this use of
iscanonical breaks C++ applications, because the builtin is only
available in C mode.

This patch provides a C++ implementation of iscanonical that relies on
function overloading, rather than builtins, to select between
floating-point types.

Unlike the C++ implementations for iszero and issignaling, this
implementation ignores __NO_LONG_DOUBLE_MATH.  The double type always
matches IEC 60559 double format, which is always canonical.  Thus, when
double and long double are the same (__NO_LONG_DOUBLE_MATH), iscanonical
always returns 1 and is not implemented with __MATH_TG.

Tested for powerpc64, powerpc64le and x86_64.

	[BZ #22235]
	* math/math.h: Trivial fix for unbalanced parentheses in comment.
	* math/Makefile [CXX] (tests): Add test-math-iscanonical.cc.
	(CFLAGS-test-math-iscanonical.cc): New variable.
	* math/test-math-iscanonical.cc: New file.
	* sysdeps/ieee754/ldbl-96/bits/iscanonical.h (iscanonical):
	Provide a C++ implementation based on function overloading,
	rather than using __MATH_TG, which uses C-only builtins.
	* sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h (iscanonical):
	Likewise.
	* sysdeps/powerpc/powerpc64le/Makefile
	(CFLAGS-test-math-iscanonical.cc): New variable.

3 files changed, 38 insertions, 3 deletions

diff --git a/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h b/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h
index 7ddb368d26..f756857c03 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..cfa36a0c2a 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: \