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Fix exp2 spurious underflows (bug 16560).

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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.
This commit is contained in:
Joseph Myers
2015-02-12 19:02:45 +00:00
parent 98408b95b1
commit 03d95bd483
9 changed files with 733 additions and 3 deletions
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9
math/e_exp2l.c
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@ -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