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| author | Joseph Myers <joseph@codesourcery.com> | 2015-09-26 00:27:06 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2015-09-26 00:27:06 +0000 |
| commit | fa752c698146ca3e9f7747d33059fbef9bb02b0e (patch) | |
| tree | a41295f8a99770d272a53c714effd0f5749b2735 /ChangeLog | |
| parent | 6ace39382120dd0668b2168591611f71b04ac8f3 (diff) | |
| download | glibc-fa752c698146ca3e9f7747d33059fbef9bb02b0e.tar.gz glibc-fa752c698146ca3e9f7747d33059fbef9bb02b0e.tar.xz glibc-fa752c698146ca3e9f7747d33059fbef9bb02b0e.zip | |
Fix powf inaccuracy (bug 18956).
The flt-32 version of powf can be inaccurate because of bugs in the extra-precision calculation of (x-1)/(x+1) or (x-1.5)/(x+1.5) as part of calculating log(x) with extra precision: a constant used (as part of adding 1 or 1.5 through integer arithmetic) is incorrect, and then the code fails to mask a computed high part before using it in arithmetic that relies on s_h*t_h being exactly representable. This patch fixes these bugs. Tested for x86_64 and x86. x86_64 ulps for powf removed and regenerated to reflect reduced ulps from the increased accuracy for existing tests. [BZ #18956] * sysdeps/ieee754/flt-32/e_powf.c (__ieee754_powf): Add 0x00400000 not 0x0040000 for high bit of mantissa. Mask with 0xfffff000 when extracting high part. * math/auto-libm-test-in: Add another test of pow. * math/auto-libm-test-out: Regenerated. * sysdeps/x86_64/fpu/libm-test-ulps: Update.
Diffstat (limited to 'ChangeLog')
| -rw-r--r-- | ChangeLog | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog index 951b3f5a4f..e70cd2fbdc 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,13 @@ +2015-09-26 Joseph Myers <joseph@codesourcery.com> + + [BZ #18956] + * sysdeps/ieee754/flt-32/e_powf.c (__ieee754_powf): Add 0x00400000 + not 0x0040000 for high bit of mantissa. Mask with 0xfffff000 when + extracting high part. + * math/auto-libm-test-in: Add another test of pow. + * math/auto-libm-test-out: Regenerated. + * sysdeps/x86_64/fpu/libm-test-ulps: Update. + 2015-09-25 Joseph Myers <joseph@codesourcery.com> [BZ #18825] |