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.

(cherry picked from commit aa0235dfdebffe9b338deba51f3ba563ee9b433d)

3 files changed, 52 insertions, 2 deletions

diff --git a/math/Makefile b/math/Makefile
index 0130fcf38b..2c17c68eda 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -203,7 +203,8 @@ tests-static = test-fpucw-static test-fpucw-ieee-static \
 	       test-signgam-ullong-static test-signgam-ullong-init-static
 
 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))
@@ -351,6 +352,7 @@ 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/math.h b/math/math.h
index f9348ec3ea..2b216c6da1 100644
--- a/math/math.h
+++ b/math/math.h
@@ -488,7 +488,7 @@ enum
       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).  */
+      and volatile)).  */
 extern "C++" {
 inline int issignaling (float __val) { return __issignalingf (__val); }
 inline int issignaling (double __val) { return __issignaling (__val); }
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>