From 7ee06ef15827f8f2582a94b1ceaad47eaf502744 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 10 Aug 2015 20:35:30 +0000 Subject: Fix ldbl-128ibm tanhl inaccuracy (bug 18790). ldbl-128ibm tanhl uses a too-small threshold to decide when to return +/-1, resulting in large errors. This patch changes it to a more appropriate threshold (the requirement is for 2*exp(-2|x|) to be small in terms of ulps of 1). Tested for x86_64, x86 and powerpc. [BZ #18790] * sysdeps/ieee754/ldbl-128ibm/s_tanhl.c (__tanhl): Increase threshold for returning +/- 1. * math/auto-libm-test-in: Add more tests of tanh. * math/auto-libm-test-out: Regenerated. * sysdeps/i386/fpu/libm-test-ulps: Update. --- sysdeps/ieee754/ldbl-128ibm/s_tanhl.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'sysdeps/ieee754/ldbl-128ibm/s_tanhl.c') diff --git a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c index c63e253..fe396e9 100644 --- a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c +++ b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c @@ -29,9 +29,9 @@ static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $"; * 2**-57 < x <= 1 : tanh(x) := -----; t = expm1(-2x) * t + 2 * 2 - * 1 <= x <= 22.0 : tanh(x) := 1- ----- ; t=expm1(2x) + * 1 <= x <= 40.0 : tanh(x) := 1- ----- ; t=expm1(2x) * t + 2 - * 22.0 < x <= INF : tanh(x) := 1. + * 40.0 < x <= INF : tanh(x) := 1. * * Special cases: * tanh(NaN) is NaN; @@ -61,8 +61,8 @@ long double __tanhl(long double x) else return one/x-one; /* tanh(NaN) = NaN */ } - /* |x| < 22 */ - if (ix < 0x4036000000000000LL) { /* |x|<22 */ + /* |x| < 40 */ + if (ix < 0x4044000000000000LL) { /* |x|<40 */ if (ix == 0) return x; /* x == +-0 */ if (ix<0x3c60000000000000LL) /* |x|<2**-57 */ @@ -74,7 +74,7 @@ long double __tanhl(long double x) t = __expm1l(-two*fabsl(x)); z= -t/(t+two); } - /* |x| > 22, return +-1 */ + /* |x| > 40, return +-1 */ } else { z = one - tiny; /* raised inexact flag */ } -- cgit v1.1