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authorJoseph Myers <joseph@codesourcery.com>2015-02-25 00:01:15 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-02-25 00:01:15 +0000
commit440169d681cc9f422e8486f1324079bef0e0c35a (patch)
tree9b732f618ba081518cf0cca84ef33328526a4633 /sysdeps/ieee754
parentba7d2c543f7d69883ece7eab39bf6c5cd5dc3081 (diff)
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Fix ldbl-128ibm acoshl inaccuracy (bug 18019).
The ldbl-128ibm implementation of acoshl uses a cut-off of 0x1p28 to determine when to use log(x) + log(2) as a formula. That cut-off is too small for this format, resulting in large errors. This patch changes it to a more appropriate cut-off of 0x1p56, adding tests around the cut-offs for various floating-point formats. Tested for powerpc. Also tested for x86_64 and x86 and updated ulps. [BZ #18019] * sysdeps/ieee754/ldbl-128ibm/e_acoshl.c (__ieee754_acoshl): Use 2**56 not 2**28 as threshold for log (2x) formula. * math/auto-libm-test-in: Add more tests of acosh. * math/auto-libm-test-out: Regenerated. * sysdeps/i386/fpu/libm-test-ulps: Update. * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
Diffstat (limited to 'sysdeps/ieee754')
-rw-r--r--sysdeps/ieee754/ldbl-128ibm/e_acoshl.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_acoshl.c b/sysdeps/ieee754/ldbl-128ibm/e_acoshl.c
index b0b33f7..cab1da9 100644
--- a/sysdeps/ieee754/ldbl-128ibm/e_acoshl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/e_acoshl.c
@@ -44,14 +44,14 @@ __ieee754_acoshl(long double x)
EXTRACT_WORDS64 (lx, xlo);
if(hx<0x3ff0000000000000LL) { /* x < 1 */
return (x-x)/(x-x);
- } else if(hx >=0x41b0000000000000LL) { /* x > 2**28 */
+ } else if(hx >=0x4370000000000000LL) { /* x >= 2**56 */
if(hx >=0x7ff0000000000000LL) { /* x is inf of NaN */
return x+x;
} else
return __ieee754_logl(x)+ln2; /* acosh(huge)=log(2x) */
} else if (((hx-0x3ff0000000000000LL)|(lx&0x7fffffffffffffffLL))==0) {
return 0.0; /* acosh(1) = 0 */
- } else if (hx > 0x4000000000000000LL) { /* 2**28 > x > 2 */
+ } else if (hx > 0x4000000000000000LL) { /* 2**56 > x > 2 */
t=x*x;
return __ieee754_logl(2.0*x-one/(x+__ieee754_sqrtl(t-one)));
} else { /* 1<x<2 */