Fix dbl-64 remainder sign of zero result (bug 19201).

For some large arguments, the dbl-64 implementation of remainder gives
zero results with the wrong sign, resulting from a subtraction that is
mathematically correct but does not guarantee that a zero result has
the sign of the first argument to remainder.  This patch adds an
appropriate check for this case, similar to other implementations of
remainder in the case of equality, and adds tests of remainder on
inputs already used to test remquo.

Tested for x86_64 and x86.

	[BZ #19201]
	* sysdeps/ieee754/dbl-64/e_remainder.c (__ieee754_remainder):
	Check for zero remainder in case of large exponents and ensure
	correct sign of result in that case.
	* math/libm-test.inc (remainder_test_data): Add more tests.

4 files changed, 79 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index d9c0689..f804371 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2015-11-02  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #19201]
+	* sysdeps/ieee754/dbl-64/e_remainder.c (__ieee754_remainder):
+	Check for zero remainder in case of large exponents and ensure
+	correct sign of result in that case.
+	* math/libm-test.inc (remainder_test_data): Add more tests.
+
 	[BZ #6799]
 	* math/s_nextafter.c: Include <errno.h>.
 	(__nextafter): Set errno on overflow and underflow.
diff --git a/NEWS b/NEWS
index 1cc08a0..896eb02 100644
--- a/NEWS
+++ b/NEWS
@@ -21,7 +21,8 @@ Version 2.23
   18966, 18967, 18969, 18970, 18977, 18980, 18981, 18982, 18985, 19003,
   19007, 19012, 19016, 19018, 19032, 19046, 19048, 19049, 19050, 19059,
   19071, 19074, 19076, 19077, 19078, 19079, 19085, 19086, 19088, 19094,
-  19095, 19124, 19125, 19129, 19134, 19137, 19156, 19174, 19181, 19189.
+  19095, 19124, 19125, 19129, 19134, 19137, 19156, 19174, 19181, 19189,
+  19201.
 
 * A defect in the malloc implementation, present since glibc 2.15 (2012) or
   glibc 2.10 via --enable-experimental-malloc (2009), could result in the
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 1267b81..2645ccc 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -10318,6 +10318,75 @@ static const struct test_ff_f_data remainder_test_data[] =
 #if defined TEST_LDOUBLE && LDBL_MANT_DIG >= 56
     TEST_ff_f (remainder, -0x1.80000000000002p1L, 2.0, 0x1.fffffffffffff8p-1L, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
 #endif
+
+    TEST_ff_f (remainder, 3419, 360, 179, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -3419, 360, -179, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 3419, -360, 179, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -3419, -360, -179, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+
+    TEST_ff_f (remainder, max_value, max_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, max_value, -max_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, max_value, min_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, max_value, -min_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, max_value, min_subnorm_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, max_value, -min_subnorm_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, max_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, -max_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, min_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, -min_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, min_subnorm_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, -min_subnorm_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_value, max_value, min_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_value, -max_value, min_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_value, min_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_value, -min_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_value, min_subnorm_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_value, -min_subnorm_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_value, max_value, -min_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_value, -max_value, -min_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_value, min_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_value, -min_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_value, min_subnorm_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_value, -min_subnorm_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_subnorm_value, max_value, min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_subnorm_value, -max_value, min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_subnorm_value, min_value, min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_subnorm_value, -min_value, min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_subnorm_value, min_subnorm_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, min_subnorm_value, -min_subnorm_value, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_subnorm_value, max_value, -min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_subnorm_value, -max_value, -min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_subnorm_value, min_value, -min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_subnorm_value, -min_value, -min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_subnorm_value, min_subnorm_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -min_subnorm_value, -min_subnorm_value, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+
+    TEST_ff_f (remainder, 1, max_value, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 1, -max_value, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 1, max_value / 2, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 1, -max_value / 2, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 1, max_value / 4, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 1, -max_value / 4, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 1, max_value / 8, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 1, -max_value / 8, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, max_value, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, -max_value, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, max_value / 2, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, -max_value / 2, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, max_value / 4, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, -max_value / 4, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, max_value / 8, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -1, -max_value / 8, -1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+
+    TEST_ff_f (remainder, max_value, max_value / 2, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, max_value, -max_value / 2, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, max_value / 2, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -max_value, -max_value / 2, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+
+    TEST_ff_f (remainder, 2, 1, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, 2, -1, plus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -2, 1, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+    TEST_ff_f (remainder, -2, -1, minus_zero, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
   };
 
 static void
diff --git a/sysdeps/ieee754/dbl-64/e_remainder.c b/sysdeps/ieee754/dbl-64/e_remainder.c
index 7f3a02b..4818091 100644
--- a/sysdeps/ieee754/dbl-64/e_remainder.c
+++ b/sysdeps/ieee754/dbl-64/e_remainder.c
@@ -130,6 +130,8 @@ __ieee754_remainder (double x, double y)
 	      d = fabs (z);
 	      if (d <= fabs (d - y))
 		return z;
+	      else if (d == y)
+		return 0.0 * x;
 	      else
 		return (z > 0) ? z - y : z + y;
 	    }