Fix sign of remquo zero remainder in round-downward mode (bug 17987).

Various remquo implementations produce a zero remainder with the wrong
sign (a zero remainder should always have the sign of the first
argument, as specified in IEEE 754) in round-downward mode, resulting
from the sign of 0 - 0.  This patch checks for zero results and fixes
their sign accordingly.

Tested for x86_64, x86, mips64 and powerpc.

	[BZ #17987]
	* sysdeps/ieee754/dbl-64/s_remquo.c (__remquo): Ensure sign of
	zero result does not depend on the sign resulting from
	subtraction.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c (__remquo):
	Likewise.
	* sysdeps/ieee754/flt-32/s_remquof.c (__remquof): Likewise.
	* sysdeps/ieee754/ldbl-128/s_remquol.c (__remquol): Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_remquol.c (__remquol): Likewise.
	* sysdeps/ieee754/ldbl-96/s_remquol.c (__remquol): Likewise.
	* math/libm-test.inc (remquo_test_data): Add more tests.

9 files changed, 43 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 540e997..f74ef23 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2015-02-16  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #17987]
+	* sysdeps/ieee754/dbl-64/s_remquo.c (__remquo): Ensure sign of
+	zero result does not depend on the sign resulting from
+	subtraction.
+	* sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c (__remquo):
+	Likewise.
+	* sysdeps/ieee754/flt-32/s_remquof.c (__remquof): Likewise.
+	* sysdeps/ieee754/ldbl-128/s_remquol.c (__remquol): Likewise.
+	* sysdeps/ieee754/ldbl-128ibm/s_remquol.c (__remquol): Likewise.
+	* sysdeps/ieee754/ldbl-96/s_remquol.c (__remquol): Likewise.
+	* math/libm-test.inc (remquo_test_data): Add more tests.
+
 2015-02-16  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* manual/time.texi (TZ Variable): glibc no longer comes with tzdata.
diff --git a/NEWS b/NEWS
index 4f4f740..1c5e590 100644
--- a/NEWS
+++ b/NEWS
@@ -10,7 +10,7 @@ Version 2.22
 * The following bugs are resolved with this release:
 
   4719, 15467, 15790, 16560, 17569, 17792, 17912, 17932, 17944, 17949,
-  17964, 17965, 17967, 17969, 17978.
+  17964, 17965, 17967, 17969, 17978, 17987.
 
 Version 2.21
 
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 1cf80e3..85d8b67 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -8818,6 +8818,16 @@ static const struct test_ffI_f1_data remquo_test_data[] =
     TEST_ffI_f1 (remquo, -1, -max_value / 4, -1, 0, NO_INEXACT_EXCEPTION),
     TEST_ffI_f1 (remquo, -1, max_value / 8, -1, 0, NO_INEXACT_EXCEPTION),
     TEST_ffI_f1 (remquo, -1, -max_value / 8, -1, 0, NO_INEXACT_EXCEPTION),
+
+    TEST_ffI_f1 (remquo, max_value, max_value / 2, plus_zero, 2, NO_INEXACT_EXCEPTION),
+    TEST_ffI_f1 (remquo, max_value, -max_value / 2, plus_zero, -2, NO_INEXACT_EXCEPTION),
+    TEST_ffI_f1 (remquo, -max_value, max_value / 2, minus_zero, -2, NO_INEXACT_EXCEPTION),
+    TEST_ffI_f1 (remquo, -max_value, -max_value / 2, minus_zero, 2, NO_INEXACT_EXCEPTION),
+
+    TEST_ffI_f1 (remquo, 2, 1, plus_zero, 2, NO_INEXACT_EXCEPTION),
+    TEST_ffI_f1 (remquo, 2, -1, plus_zero, -2, NO_INEXACT_EXCEPTION),
+    TEST_ffI_f1 (remquo, -2, 1, minus_zero, -2, NO_INEXACT_EXCEPTION),
+    TEST_ffI_f1 (remquo, -2, -1, minus_zero, 2, NO_INEXACT_EXCEPTION),
   };
 
 static void
diff --git a/sysdeps/ieee754/dbl-64/s_remquo.c b/sysdeps/ieee754/dbl-64/s_remquo.c
index e07efa8..b081d26 100644
--- a/sysdeps/ieee754/dbl-64/s_remquo.c
+++ b/sysdeps/ieee754/dbl-64/s_remquo.c
@@ -101,6 +101,9 @@ __remquo (double x, double y, int *quo)
 
   *quo = qs ? -cquo : cquo;
 
+  /* Ensure correct sign of zero result in round-downward mode.  */
+  if (x == 0.0)
+    x = 0.0;
   if (sx)
     x = -x;
   return x;
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c
index ab56178..304e9d0 100644
--- a/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c
+++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c
@@ -100,6 +100,9 @@ __remquo (double x, double y, int *quo)
 
   *quo = qs ? -cquo : cquo;
 
+  /* Ensure correct sign of zero result in round-downward mode.  */
+  if (x == 0.0)
+    x = 0.0;
   if (sx)
     x = -x;
   return x;
diff --git a/sysdeps/ieee754/flt-32/s_remquof.c b/sysdeps/ieee754/flt-32/s_remquof.c
index 04944fd..36cf359 100644
--- a/sysdeps/ieee754/flt-32/s_remquof.c
+++ b/sysdeps/ieee754/flt-32/s_remquof.c
@@ -100,6 +100,9 @@ __remquof (float x, float y, int *quo)
 
   *quo = qs ? -cquo : cquo;
 
+  /* Ensure correct sign of zero result in round-downward mode.  */
+  if (x == 0.0f)
+    x = 0.0f;
   if (sx)
     x = -x;
   return x;
diff --git a/sysdeps/ieee754/ldbl-128/s_remquol.c b/sysdeps/ieee754/ldbl-128/s_remquol.c
index da175a1..82cdf1a 100644
--- a/sysdeps/ieee754/ldbl-128/s_remquol.c
+++ b/sysdeps/ieee754/ldbl-128/s_remquol.c
@@ -102,6 +102,9 @@ __remquol (long double x, long double y, int *quo)
 
   *quo = qs ? -cquo : cquo;
 
+  /* Ensure correct sign of zero result in round-downward mode.  */
+  if (x == 0.0L)
+    x = 0.0L;
   if (sx)
     x = -x;
   return x;
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_remquol.c b/sysdeps/ieee754/ldbl-128ibm/s_remquol.c
index ac22879..57c5059 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_remquol.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_remquol.c
@@ -107,6 +107,9 @@ __remquol (long double x, long double y, int *quo)
 
   *quo = qs ? -cquo : cquo;
 
+  /* Ensure correct sign of zero result in round-downward mode.  */
+  if (x == 0.0L)
+    x = 0.0L;
   if (sx)
     x = -x;
   return x;
diff --git a/sysdeps/ieee754/ldbl-96/s_remquol.c b/sysdeps/ieee754/ldbl-96/s_remquol.c
index 1462b54..8d6b10e 100644
--- a/sysdeps/ieee754/ldbl-96/s_remquol.c
+++ b/sysdeps/ieee754/ldbl-96/s_remquol.c
@@ -101,6 +101,9 @@ __remquol (long double x, long double p, int *quo)
 
   *quo = qs ? -cquo : cquo;
 
+  /* Ensure correct sign of zero result in round-downward mode.  */
+  if (x == 0.0L)
+    x = 0.0L;
   if (sx)
     x = -x;
   return x;