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authorJoseph Myers <joseph@codesourcery.com>2015-12-09 21:20:18 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-12-09 21:20:18 +0000
commitca2fcac629b9b7781ccd52685b28741d89ff128f (patch)
tree8c2b6491a4672a338e965e8ca1fa0f8724d189a6 /sysdeps
parente5a5315e2d290fe34e0fb80996c713b8b802dcc9 (diff)
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Fix ldbl-128ibm tanhl inaccuracy for small arguments (bug 19349).
The ldbl-128ibm implementation of tanhl is inaccurate for small arguments, because it returns x*(1+x) (maybe in an attempt to raise "inexact") when x itself would be the accurate return value but multiplying by 1+x introduces large errors. This patch fixes it to return x in that case (when the mathematical result is x plus a negligible remainder on the order of x^3) to avoid those errors. Tested for powerpc. [BZ #19349] * sysdeps/ieee754/ldbl-128ibm/s_tanhl.c (__tanhl): Return argument when small.
Diffstat (limited to 'sysdeps')
-rw-r--r--sysdeps/ieee754/ldbl-128ibm/s_tanhl.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
index 292020c..e6457a1 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
@@ -69,7 +69,7 @@ long double __tanhl(long double x)
if (ix<0x3c60000000000000LL) /* |x|<2**-57 */
{
math_check_force_underflow (x);
- return x*(one+x); /* tanh(small) = small */
+ return x; /* tanh(small) = small */
}
if (ix>=0x3ff0000000000000LL) { /* |x|>=1 */
t = __expm1l(two*fabsl(x));