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author | Joseph Myers <joseph@codesourcery.com> | 2015-01-12 23:02:14 +0000 |
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committer | Joseph Myers <joseph@codesourcery.com> | 2015-01-12 23:02:14 +0000 |
commit | 5a9e4c09a2601a8100ea9a1f7bc0360782cd1625 (patch) | |
tree | f70efee88fe34c9f405165c4241978724ccf3282 /sysdeps/ieee754 | |
parent | 34e93d6c76b7a6eaf94697a172b958704fd33396 (diff) | |
download | glibc-5a9e4c09a2601a8100ea9a1f7bc0360782cd1625.zip glibc-5a9e4c09a2601a8100ea9a1f7bc0360782cd1625.tar.gz glibc-5a9e4c09a2601a8100ea9a1f7bc0360782cd1625.tar.bz2 |
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.c | 8 |
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; } |