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. --- math/e_exp2l.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'math/e_exp2l.c') diff --git a/math/e_exp2l.c b/math/e_exp2l.c index bb7feefeff..9eb7bafadd 100644 --- a/math/e_exp2l.c +++ b/math/e_exp2l.c @@ -20,6 +20,13 @@ #include #include +/* To avoid spurious underflows, use this definition to treat IBM long + double as approximating an IEEE-style format. */ +#if LDBL_MANT_DIG == 106 +# undef LDBL_EPSILON +# define LDBL_EPSILON 0x1p-106L +#endif + long double __ieee754_exp2l (long double x) { @@ -31,6 +38,8 @@ __ieee754_exp2l (long double x) { int intx = (int) x; long double fractx = x - intx; + if (fabsl (fractx) < LDBL_EPSILON / 4.0L) + return __scalbnl (1.0L + fractx, intx); return __scalbnl (__ieee754_expl (M_LN2l * fractx), intx); } else -- cgit v1.2.3