From a04bb3306a9f9f17e5c588c903a438f1182ecd1a Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Wed, 1 Jul 2015 22:27:49 +0000 Subject: Fix ldbl-128 expm1l (-min_subnorm) result sign (bug 18619). 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. [BZ #18619] * sysdeps/ieee754/ldbl-128/s_expm1l.c (__expm1l): Force underflow and return argument in case of subnormal argument. --- sysdeps/ieee754/ldbl-128/s_expm1l.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) (limited to 'sysdeps/ieee754') 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. */ -- cgit v1.1