2017-08-28  Gabriel F. T. Gomes  <gftg@linux.vnet.ibm.com>

	[BZ #21930]
	* math/math.h [defined __cplusplus && defined __SUPPORT_SNAN__]
	(iszero): New C++ implementation that does not use
	fpclassify/__MATH_TG/__builtin_types_compatible_p, when
	signaling nans are enabled, since __builtin_types_compatible_p
	is a C-only feature.

2017-08-24  Gabriel F. T. Gomes  <gftg@linux.vnet.ibm.com>

	* math/math.h [defined __cplusplus] (issignaling): In the long
	double case, call __issignalingl only if __NO_LONG_DOUBLE_MATH
	is not defined.  Call __issignaling, otherwise.

2017-08-22  Gabriel F. T. Gomes  <gftg@linux.vnet.ibm.com>

	* math/math.h [defined __cplusplus] (issignaling): Provide a C++
	definition for issignaling that does not rely on __MATH_TG,
	since __MATH_TG uses __builtin_types_compatible_p, which is only
	available in C mode.

2017-08-18  Gabriel F. T. Gomes  <gftg@linux.vnet.ibm.com>

	[BZ #21930]
	* math/math.h (isinf): Check if in C or C++ mode before using
	__builtin_types_compatible_p, since this is a C mode feature.

Index: glibc-2.26/math/math.h
===================================================================
--- glibc-2.26.orig/math/math.h
+++ glibc-2.26/math/math.h
@@ -442,8 +442,12 @@ enum
 
 /* Return nonzero value if X is positive or negative infinity.  */
 # if __HAVE_DISTINCT_FLOAT128 && !__GNUC_PREREQ (7,0) \
-     && !defined __SUPPORT_SNAN__
-   /* __builtin_isinf_sign is broken for float128 only before GCC 7.0.  */
+     && !defined __SUPPORT_SNAN__ && !defined __cplusplus
+   /* Since __builtin_isinf_sign is broken for float128 before GCC 7.0,
+      use the helper function, __isinff128, with older compilers.  This is
+      only provided for C mode, because in C++ mode, GCC has no support
+      for __builtin_types_compatible_p (and when in C++ mode, this macro is
+      not used anyway, because libstdc++ headers undefine it).  */
 #  define isinf(x) \
     (__builtin_types_compatible_p (__typeof (x), _Float128) \
      ? __isinff128 (x) : __builtin_isinf_sign (x))
@@ -470,7 +474,32 @@ enum
 # include <bits/iscanonical.h>
 
 /* Return nonzero value if X is a signaling NaN.  */
-# define issignaling(x) __MATH_TG ((x), __issignaling, (x))
+# ifndef __cplusplus
+#  define issignaling(x) __MATH_TG ((x), __issignaling, (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 issignaling (float __val) { return __issignalingf (__val); }
+inline int issignaling (double __val) { return __issignaling (__val); }
+inline int
+issignaling (long double __val)
+{
+#  ifdef __NO_LONG_DOUBLE_MATH
+  return __issignaling (__val);
+#  else
+  return __issignalingl (__val);
+#  endif
+}
+#  if __HAVE_DISTINCT_FLOAT128
+inline int issignaling (_Float128 __val) { return __issignalingf128 (__val); }
+#  endif
+} /* extern C++ */
+# endif
 
 /* Return nonzero value if X is subnormal.  */
 # define issubnormal(x) (fpclassify (x) == FP_SUBNORMAL)
@@ -484,15 +513,40 @@ enum
 #  endif
 # else	/* __cplusplus */
 extern "C++" {
+#  ifdef __SUPPORT_SNAN__
+inline int
+iszero (float __val)
+{
+  return __fpclassifyf (__val) == FP_ZERO;
+}
+inline int
+iszero (double __val)
+{
+  return __fpclassify (__val) == FP_ZERO;
+}
+inline int
+iszero (long double __val)
+{
+#   ifdef __NO_LONG_DOUBLE_MATH
+  return __fpclassify (__val) == FP_ZERO;
+#   else
+  return __fpclassifyl (__val) == FP_ZERO;
+#   endif
+}
+#   if __HAVE_DISTINCT_FLOAT128
+inline int
+iszero (_Float128 __val)
+{
+  return __fpclassifyf128 (__val) == FP_ZERO;
+}
+#   endif
+#  else
 template <class __T> inline bool
 iszero (__T __val)
 {
-#  ifdef __SUPPORT_SNAN__
-  return fpclassify (__val) == FP_ZERO;
-#  else
   return __val == 0;
-#  endif
 }
+#  endif
 } /* extern C++ */
 # endif	/* __cplusplus */
 #endif /* Use IEC_60559_BFP_EXT.  */