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authorJoseph Myers <joseph@codesourcery.com>2015-02-16 22:38:28 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-02-16 22:38:28 +0000
commita820f9b3c0cb5e80cd892b0f9c1c48f48bd4413f (patch)
treee563669e7d00f3eeab3c3b8f34ddd77339c57def /sysdeps/ieee754/ldbl-96
parentbe802953a103bfd502d696f1418e2bef1b450be2 (diff)
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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.
Diffstat (limited to 'sysdeps/ieee754/ldbl-96')
-rw-r--r--sysdeps/ieee754/ldbl-96/s_remquol.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/sysdeps/ieee754/ldbl-96/s_remquol.c b/sysdeps/ieee754/ldbl-96/s_remquol.c
index 6b3499d257..1462b54456 100644
--- a/sysdeps/ieee754/ldbl-96/s_remquol.c
+++ b/sysdeps/ieee754/ldbl-96/s_remquol.c
@@ -60,12 +60,12 @@ __remquol (long double x, long double p, int *quo)
   p  = fabsl (p);
   cquo = 0;
 
-  if (x >= 4 * p)
+  if (ep <= 0x7ffc && x >= 4 * p)
     {
       x -= 4 * p;
       cquo += 4;
     }
-  if (x >= 2 * p)
+  if (ep <= 0x7ffd && x >= 2 * p)
     {
       x -= 2 * p;
       cquo += 2;