Fix remquo spurious overflows (bug 17978).

Various remquo implementations, when computing the last three bits of
the quotient, have spurious overflows when 4 times the second argument
to remquo overflows.  These overflows can in turn cause bad results in
rounding modes where that overflow results in a finite value.  This
patch adds tests to avoid the problem multiplications in cases where
they would overflow, similar to those that control an earlier
multiplication by 8.

Tested for x86_64, x86, mips64 and powerpc.

	[BZ #17978]
	* sysdeps/ieee754/dbl-64/s_remquo.c (__remquo): Do not form
	products 4 * y and 2 * y where those would overflow.
	* 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.

1 files changed, 2 insertions, 2 deletions

diff --git a/sysdeps/ieee754/dbl-64/s_remquo.c b/sysdeps/ieee754/dbl-64/s_remquo.c
index 2724902908..e07efa89f8 100644
--- a/sysdeps/ieee754/dbl-64/s_remquo.c
+++ b/sysdeps/ieee754/dbl-64/s_remquo.c
@@ -60,12 +60,12 @@ __remquo (double x, double y, int *quo)
   y = fabs (y);
   cquo = 0;
 
-  if (x >= 4 * y)
+  if (hy <= 0x7fcfffff && x >= 4 * y)
     {
       x -= 4 * y;
       cquo += 4;
     }
-  if (x >= 2 * y)
+  if (hy <= 0x7fdfffff && x >= 2 * y)
     {
       x -= 2 * y;
       cquo += 2;