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| author | Joseph Myers <joseph@codesourcery.com> | 2015-02-12 19:02:45 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2015-02-12 19:02:45 +0000 |
| commit | 03d95bd48319256bd29cfaece45919fc58bf56cc (patch) | |
| tree | 5ed21769ade47b69e555932587a23f69201c7ba6 /math/e_exp2l.c | |
| parent | 98408b95b155464e760c22dce4842f29499db821 (diff) | |
| download | glibc-03d95bd48319256bd29cfaece45919fc58bf56cc.tar.gz glibc-03d95bd48319256bd29cfaece45919fc58bf56cc.tar.xz glibc-03d95bd48319256bd29cfaece45919fc58bf56cc.zip | |
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.
Diffstat (limited to 'math/e_exp2l.c')
| -rw-r--r-- | math/e_exp2l.c | 9 |
1 files changed, 9 insertions, 0 deletions
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 <math_private.h> #include <float.h> +/* 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 |