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.

1 files changed, 2 insertions, 0 deletions

diff --git a/sysdeps/ieee754/dbl-64/e_remainder.c b/sysdeps/ieee754/dbl-64/e_remainder.c
index 7f3a02b3c2..4818091231 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;
 	    }