Provide a C++ version of issignaling that does not use __MATH_TG

The macro __MATH_TG contains the logic to select between long double and
_Float128, when these types are ABI-distinct.  This logic relies on
__builtin_types_compatible_p, which is not available in C++ mode.

On the other hand, C++ function 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.

Tested for powerpc64le, s390x, and x86_64.

	* 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.
	(CFLAGS-test-math-issignaling.cc): New variable.
	* math/Makefile [CXX] (tests): Add test-math-issignaling.
	* math/test-math-issignaling.cc: New test for C++ implementation
	of type-generic issignaling.
	* sysdeps/powerpc/powerpc64le/Makefile [subdir == math]
	(CXXFLAGS-test-math-issignaling.cc): Add -mfloat128 to the build
	options of test-math-issignaling on powerpc64le.

3 files changed, 133 insertions, 2 deletions

diff --git a/math/Makefile b/math/Makefile
index fb79b801cf..9e88cfc637 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -208,7 +208,7 @@ tests-internal = test-matherr test-matherr-2
 tests-static += atest-exp atest-sincos atest-exp2
 
 ifneq (,$(CXX))
-tests += test-math-isinff test-math-iszero
+tests += test-math-isinff test-math-iszero test-math-issignaling
 endif
 
 ifneq (no,$(PERL))
@@ -355,6 +355,7 @@ 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-iszero-excess-precision.c = -fexcess-precision=standard
 CFLAGS-test-iseqsig-excess-precision.c = -fexcess-precision=standard
diff --git a/math/math.h b/math/math.h
index 275534be11..b5d6c43fcf 100644
--- a/math/math.h
+++ b/math/math.h
@@ -474,7 +474,24 @@ 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) { return __issignalingl (__val); }
+#  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)
diff --git a/math/test-math-issignaling.cc b/math/test-math-issignaling.cc
new file mode 100644
index 0000000000..22ae9e1bca
--- /dev/null
+++ b/math/test-math-issignaling.cc
@@ -0,0 +1,113 @@
+/* Test for the C++ implementation of issignaling.
+   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>
+
+#include <limits>
+
+/* There is no signaling_NaN for _Float128 in std::numeric_limits.
+   Include ieee754_float128.h and use the bitfields in the union
+   ieee854_float128.ieee_nan to build a signaling NaN.  */
+#if __HAVE_DISTINCT_FLOAT128
+# include <ieee754_float128.h>
+#endif
+
+static bool errors;
+
+static void
+check (int actual, int expected, const char *actual_expr, int line)
+{
+  if (actual != expected)
+    {
+      errors = true;
+      printf ("%s:%d: error: %s\n", __FILE__, line, actual_expr);
+      printf ("%s:%d:   expected: %d\n", __FILE__, line, expected);
+      printf ("%s:%d:   actual: %d\n", __FILE__, line, actual);
+    }
+}
+
+#define CHECK(actual, expected) \
+  check ((actual), (expected), #actual, __LINE__)
+
+template <class T>
+static void
+check_type ()
+{
+  typedef std::numeric_limits<T> limits;
+  CHECK (issignaling (T{0}), 0);
+  if (limits::has_infinity)
+    {
+      CHECK (issignaling (limits::infinity ()), 0);
+      CHECK (issignaling (-limits::infinity ()), 0);
+    }
+  if (limits::has_quiet_NaN)
+    CHECK (issignaling (limits::quiet_NaN ()), 0);
+  if (limits::has_signaling_NaN)
+    CHECK (issignaling (limits::signaling_NaN ()), 1);
+}
+
+#if __HAVE_DISTINCT_FLOAT128
+static void
+check_float128 ()
+{
+  ieee854_float128 q;
+
+  q.d = 0;
+  CHECK (issignaling (q.d), 0);
+
+  /* Infinity.  */
+  q.ieee.negative = 0;
+  q.ieee.exponent = 0x7FFF;
+  q.ieee.mantissa0 = 0x0000;
+  q.ieee.mantissa1 = 0x00000000;
+  q.ieee.mantissa2 = 0x00000000;
+  q.ieee.mantissa3 = 0x00000000;
+  CHECK (issignaling (q.d), 0);
+
+  /* Quiet NaN.  */
+  q.ieee_nan.quiet_nan = 1;
+  q.ieee_nan.mantissa0 = 0x0000;
+  CHECK (issignaling (q.d), 0);
+
+  /* Still a quiet NaN.  */
+  q.ieee_nan.quiet_nan = 1;
+  q.ieee_nan.mantissa0 = 0x4000;
+  CHECK (issignaling (q.d), 0);
+
+  /* Signaling NaN.  */
+  q.ieee_nan.quiet_nan = 0;
+  q.ieee_nan.mantissa0 = 0x4000;
+  CHECK (issignaling (q.d), 1);
+}
+#endif
+
+static int
+do_test (void)
+{
+  check_type<float> ();
+  check_type<double> ();
+  check_type<long double> ();
+#if __HAVE_DISTINCT_FLOAT128
+  check_float128 ();
+#endif
+  return errors;
+}
+
+#include <support/test-driver.c>