From 03d95bd48319256bd29cfaece45919fc58bf56cc Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Thu, 12 Feb 2015 19:02:45 +0000 Subject: Fix exp2 spurious underflows (bug 16560). This patch fixes the remaining part of bug 16560, spurious underflows from exp2 of arguments close to 0 (when the result is close to 1, so should not underflow), by just using 1+x instead of a more complicated calculation when the argument is sufficiently small. Tested for x86_64, x86 and mips64. [BZ #16560] * math/e_exp2l.c [LDBL_MANT_DIG == 106] (LDBL_EPSILON): Undefine and redefine. (__ieee754_exp2l): Do not multiply small fractional parts by M_LN2l. * sysdeps/i386/fpu/e_exp2l.S (__ieee754_exp2l): Just add 1 to small argument. * sysdeps/ieee754/dbl-64/e_exp2.c (__ieee754_exp2): Likewise. * sysdeps/ieee754/flt-32/e_exp2f.c (__ieee754_exp2f): Likewise. * sysdeps/x86_64/fpu/e_exp2l.S (__ieee754_exp2l): Likewise. * math/auto-libm-test-in: Add more tests of exp2. * math/auto-libm-test-out: Regenerated. --- sysdeps/ieee754/dbl-64/e_exp2.c | 3 +++ sysdeps/ieee754/flt-32/e_exp2f.c | 3 +++ 2 files changed, 6 insertions(+) (limited to 'sysdeps/ieee754') diff --git a/sysdeps/ieee754/dbl-64/e_exp2.c b/sysdeps/ieee754/dbl-64/e_exp2.c index 3666c6a..f964a5a 100644 --- a/sysdeps/ieee754/dbl-64/e_exp2.c +++ b/sysdeps/ieee754/dbl-64/e_exp2.c @@ -61,6 +61,9 @@ __ieee754_exp2 (double x) double rx, x22, result; union ieee754_double ex2_u, scale_u; + if (fabs (x) < DBL_EPSILON / 4.0) + return 1.0 + x; + { SET_RESTORE_ROUND_NOEX (FE_TONEAREST); diff --git a/sysdeps/ieee754/flt-32/e_exp2f.c b/sysdeps/ieee754/flt-32/e_exp2f.c index 01cd444..f3e3a8e 100644 --- a/sysdeps/ieee754/flt-32/e_exp2f.c +++ b/sysdeps/ieee754/flt-32/e_exp2f.c @@ -54,6 +54,9 @@ __ieee754_exp2f (float x) float rx, x22, result; union ieee754_float ex2_u, scale_u; + if (fabsf (x) < FLT_EPSILON / 4.0f) + return 1.0f + x; + { SET_RESTORE_ROUND_NOEXF (FE_TONEAREST); -- cgit v1.1