diff options
| author | Joseph Myers <joseph@codesourcery.com> | 2015-12-09 21:20:18 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2015-12-09 21:20:18 +0000 |
| commit | ca2fcac629b9b7781ccd52685b28741d89ff128f (patch) | |
| tree | 8c2b6491a4672a338e965e8ca1fa0f8724d189a6 | |
| parent | e5a5315e2d290fe34e0fb80996c713b8b802dcc9 (diff) | |
| download | glibc-ca2fcac629b9b7781ccd52685b28741d89ff128f.zip glibc-ca2fcac629b9b7781ccd52685b28741d89ff128f.tar.gz glibc-ca2fcac629b9b7781ccd52685b28741d89ff128f.tar.bz2 | |
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.
| -rw-r--r-- | ChangeLog | 4 | ||||
| -rw-r--r-- | sysdeps/ieee754/ldbl-128ibm/s_tanhl.c | 2 |
2 files changed, 5 insertions, 1 deletions
@@ -1,5 +1,9 @@ 2015-12-09 Joseph Myers <joseph@codesourcery.com> + [BZ #19349] + * sysdeps/ieee754/ldbl-128ibm/s_tanhl.c (__tanhl): Return argument + when small. + * sysdeps/unix/sysv/linux/i386/kernel-features.h [__LINUX_KERNEL_VERSION >= 0x040300] (__ASSUME_SOCKET_SYSCALL): New macro. 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)); |