From 5a9e4c09a2601a8100ea9a1f7bc0360782cd1625 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 12 Jan 2015 23:02:14 +0000 Subject: 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. --- sysdeps/ieee754/ldbl-96/s_scalblnl.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'sysdeps/ieee754/ldbl-96') diff --git a/sysdeps/ieee754/ldbl-96/s_scalblnl.c b/sysdeps/ieee754/ldbl-96/s_scalblnl.c index 5c2f38eafd..457e999c6c 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; } -- cgit 1.4.1