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Fix ldbl-128ibm logl inaccuracy near 1 (bug 19351).

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The ldbl-128ibm implementation of logl is inaccurate for arguments
near 1, because when deciding whether to bypass a series expansion for
log(1+z), where z = x-1, it compares the square of z rather than z
itself with an epsilon value.  This patch fixes that comparison, so
eliminating the test failures for inaccuracy of logl in such cases.

Tested for powerpc.

	[BZ #19351]
	* sysdeps/ieee754/ldbl-128ibm/e_logl.c (__ieee754_logl): When
	expanding log(1+z), compare z rather than its square with epsilon
	to determine when to avoid evaluating the expansion.
This commit is contained in:
Joseph Myers 2015-12-09 23:51:11 +00:00
parent f517e06ab7
commit e6a6b1c3de
2 changed files with 6 additions and 1 deletions
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5
ChangeLog
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@ -1,5 +1,10 @@
2015-12-09 Joseph Myers <joseph@codesourcery.com>
[BZ #19351]
* sysdeps/ieee754/ldbl-128ibm/e_logl.c (__ieee754_logl): When
expanding log(1+z), compare z rather than its square with epsilon
to determine when to avoid evaluating the expansion.
[BZ #19350]
* sysdeps/ieee754/ldbl-128ibm/e_sinhl.c (__ieee754_sinhl):
Increase overflow threshold.

2
sysdeps/ieee754/ldbl-128ibm/e_logl.c
View File

@ -270,7 +270,7 @@ __ieee754_logl(long double x)
/* Series expansion of log(1+z). */
w = z * z;
/* Avoid spurious underflows. */
if (__glibc_unlikely(w <= ldbl_epsilon))
if (__glibc_unlikely (fabsl (z) <= ldbl_epsilon))
y = 0.0L;
else
{