From 913d03c864ea2547e97f8d2d30fc71a008d4d103 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Wed, 14 May 2014 12:35:40 +0000 Subject: Fix acosh (1) in round-downward mode (bug 16927). According to C99 and C11 Annex F, acosh (1) should be +0 in all rounding modes. However, some implementations in glibc wrongly return -0 in round-downward mode (which is what you get if you end up computing log1p (-0), via 1 - 1 being -0 in round-downward mode). This patch fixes the problem implementations, by correcting the test for an exact 1 value in the ldbl-96 implementation to allow for the explicit high bit of the mantissa, and by inserting fabs instructions in the i386 implementations; tests of acosh are duly converted to ALL_RM_TEST. I believe all the other sysdeps/ieee754 implementations are already OK (I haven't checked the ia64 versions, but if buggy then that will be obvious from the results of test runs after this patch is in). Tested x86_64 and x86 and ulps updated accordingly. [BZ #16927] * sysdeps/i386/fpu/e_acosh.S (__ieee754_acosh): Use fabs on x-1 value. * sysdeps/i386/fpu/e_acoshf.S (__ieee754_acoshf): Likewise. * sysdeps/i386/fpu/e_acoshl.S (__ieee754_acoshl): Likewise. * sysdeps/ieee754/ldbl-96/e_acoshl.c (__ieee754_acoshl): Correct for explicit high bit of mantissa when testing for argument equal to 1. * math/libm-test.inc (acosh_test): Use ALL_RM_TEST. * sysdeps/i386/fpu/libm-test-ulps: Update. * sysdeps/x86_64/fpu/libm-test-ulps: Likewise. --- sysdeps/ieee754/ldbl-96/e_acoshl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'sysdeps/ieee754/ldbl-96/e_acoshl.c') diff --git a/sysdeps/ieee754/ldbl-96/e_acoshl.c b/sysdeps/ieee754/ldbl-96/e_acoshl.c index bbaef68..cf9a6db 100644 --- a/sysdeps/ieee754/ldbl-96/e_acoshl.c +++ b/sysdeps/ieee754/ldbl-96/e_acoshl.c @@ -48,7 +48,7 @@ __ieee754_acoshl(long double x) return x+x; } else return __ieee754_logl(x)+ln2; /* acoshl(huge)=logl(2x) */ - } else if(((se-0x3fff)|i0|i1)==0) { + } else if(((se-0x3fff)|(i0^0x80000000)|i1)==0) { return 0.0; /* acosh(1) = 0 */ } else if (se > 0x4000) { /* 2**28 > x > 2 */ t=x*x; -- cgit v1.1