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authorJoseph Myers <joseph@codesourcery.com>2015-01-12 23:02:14 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-01-12 23:02:14 +0000
commit5a9e4c09a2601a8100ea9a1f7bc0360782cd1625 (patch)
treef70efee88fe34c9f405165c4241978724ccf3282 /sysdeps/ieee754
parent34e93d6c76b7a6eaf94697a172b958704fd33396 (diff)
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Fix ldbl-96 scalblnl underflowing results (bug 17803).
The ldbl-96 implementation of scalblnl (used for x86_64 and ia64) uses a condition k <= -63 to determine when a standard underflowing result tiny*__copysignl(tiny,x) should be returned. However, that condition corresponds to values with exponent -16446 or less, and in the case of -16446, the correct result for round-to-nearest depends on whether the value is exactly 0x1p-16446 (half the least subnormal) or more than that. This patch fixes the bug by changing the condition to k <= -64 and accordingly adjusting the exponent by 64 not 63 when converting to a normal value. Tested for x86_64. [BZ #17803] * sysdeps/ieee754/ldbl-96/s_scalblnl.c (twom63): Rename to twom64. Adjust value to 0x1p-64L. (__scalblnl): Only return standard underflowing result for K <= -64 not K <= -63; adjust exponent for underflowing result by 64 not 63. * math/libm-test.inc (scalbn_test_data): Add more tests. (scalbln_test_data): Likewise.
Diffstat (limited to 'sysdeps/ieee754')
-rw-r--r--sysdeps/ieee754/ldbl-96/s_scalblnl.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/sysdeps/ieee754/ldbl-96/s_scalblnl.c b/sysdeps/ieee754/ldbl-96/s_scalblnl.c
index 5c2f38e..457e999 100644
--- a/sysdeps/ieee754/ldbl-96/s_scalblnl.c
+++ b/sysdeps/ieee754/ldbl-96/s_scalblnl.c
@@ -26,7 +26,7 @@
static const long double
two63 = 0x1p63L,
-twom63 = 1.08420217248550443400e-19,
+twom64 = 0x1p-64L,
huge = 1.0e+4900L,
tiny = 1.0e-4900L;
@@ -52,9 +52,9 @@ __scalblnl (long double x, long int n)
k = k+n;
if (__builtin_expect(k > 0, 1)) /* normal result */
{SET_LDOUBLE_EXP(x,(es&0x8000)|k); return x;}
- if (k <= -63)
+ if (k <= -64)
return tiny*__copysignl(tiny,x); /*underflow*/
- k += 63; /* subnormal result */
+ k += 64; /* subnormal result */
SET_LDOUBLE_EXP(x,(es&0x8000)|k);
- return x*twom63;
+ return x*twom64;
}