From fa752c698146ca3e9f7747d33059fbef9bb02b0e Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Sat, 26 Sep 2015 00:27:06 +0000 Subject: 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. --- ChangeLog | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'ChangeLog') diff --git a/ChangeLog b/ChangeLog index 951b3f5a4f..e70cd2fbdc 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,13 @@ +2015-09-26 Joseph Myers + + [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 [BZ #18825] -- cgit 1.4.1