Fix ldbl-128ibm remainderl equality test for zero low part (bug 19677).

The ldbl-128ibm implementation of remainderl has logic resulting in
incorrect tests for equality of the absolute values of the arguments
in the case of zero low parts.  If the low parts are both zero but
with different signs, this can wrongly cause equal arguments to be
treated as different, resulting in turn in incorrect signs of zero
result in nondefault rounding modes arising from the subtractions done
when the arguments are not equal.

This patch fixes the logic to convert -0 low parts into +0 before the
comparison (remquo already has separate logic to deal with signs of
zero results, so doesn't need such a change).  Tests are added for
remainderl and remquol similar to that for fmodl, and based on a
refactoring of it, since the bug depends on low parts which should not
be relied upon in tests not setting the representation explicitly
(although in fact the bug shows up in test-ldouble with current GCC).
Tested for powerpc.

	[BZ #19677]
	* sysdeps/ieee754/ldbl-128ibm/e_remainderl.c
	(__ieee754_remainderl): Put zero low parts in canonical form.
	* sysdeps/ieee754/ldbl-128ibm/test-fmodrem-ldbl-128ibm.c: New
	file.  Based on
	sysdeps/ieee754/ldbl-128ibm/test-fmodl-ldbl-128ibm.c.
	* sysdeps/ieee754/ldbl-128ibm/test-fmodl-ldbl-128ibm.c: Replace
	with wrapper round test-fmodrem-ldbl-128ibm.c.
	* sysdeps/ieee754/ldbl-128ibm/test-remainderl-ldbl-128ibm.c: New
	file.
	* sysdeps/ieee754/ldbl-128ibm/test-remquol-ldbl-128ibm.c:
	Likewise.
	* sysdeps/ieee754/ldbl-128ibm/Makefile (tests): Add
	test-remainderl-ldbl-128ibm and test-remquol-ldbl-128ibm.

1 files changed, 21 insertions, 0 deletions

diff --git a/sysdeps/ieee754/ldbl-128ibm/test-remainderl-ldbl-128ibm.c b/sysdeps/ieee754/ldbl-128ibm/test-remainderl-ldbl-128ibm.c
new file mode 100644
index 0000000000..767a6700c8
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128ibm/test-remainderl-ldbl-128ibm.c
@@ -0,0 +1,21 @@
+/* Test for ldbl-128ibm remainderl handling of equal values (bug 19677).
+   Copyright (C) 2016 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 FUNC remainderl
+#define SETUP fesetround (FE_DOWNWARD)
+#include "test-fmodrem-ldbl-128ibm.c"