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Fix ldbl-128 expm1l (-min_subnorm) result sign (bug 18619) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Wed, 1 Jul 2015 22:28:41 +0000
- Subject: Fix ldbl-128 expm1l (-min_subnorm) result sign (bug 18619) [committed]
- Authentication-results: sourceware.org; auth=none
In the ldbl-128 implementation of expm1l, when expm1l's result should
underflow to 0 (argument minus the least subnormal, in some rounding
modes), it can be a zero of the wrong sign. This patch fixes this in
the same way previously used for the x86 / x86_64 versions.
Tested for mips64. Committed.
2015-07-01 Joseph Myers <joseph@codesourcery.com>
[BZ #18619]
* sysdeps/ieee754/ldbl-128/s_expm1l.c (__expm1l): Force underflow
and return argument in case of subnormal argument.
diff --git a/sysdeps/ieee754/ldbl-128/s_expm1l.c b/sysdeps/ieee754/ldbl-128/s_expm1l.c
index f708af5..573d00b 100644
--- a/sysdeps/ieee754/ldbl-128/s_expm1l.c
+++ b/sysdeps/ieee754/ldbl-128/s_expm1l.c
@@ -137,9 +137,18 @@ __expm1l (long double x)
if (x < minarg)
return (4.0/big - 1.0L);
- /* Avoid internal underflow when result does not underflow. */
- if (fabsl (x) < 0x1p-113L && fabsl (x) >= LDBL_MIN)
- return x;
+ /* Avoid internal underflow when result does not underflow, while
+ ensuring underflow (without returning a zero of the wrong sign)
+ when the result does underflow. */
+ if (fabsl (x) < 0x1p-113L)
+ {
+ if (fabsl (x) < LDBL_MIN)
+ {
+ long double force_underflow = x * x;
+ math_force_eval (force_underflow);
+ }
+ return x;
+ }
/* Express x = ln 2 (k + remainder), remainder not exceeding 1/2. */
xx = C1 + C2; /* ln 2. */
--
Joseph S. Myers
joseph@codesourcery.com