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| author | Fabian Schriever <fabian.schriever@gtd-gmbh.de> | 2020-12-11 16:57:35 +0100 |
|---|---|---|
| committer | Jeff Johnston <jjohnstn@redhat.com> | 2020-12-11 14:38:19 -0500 |
| commit | cf1ef2dc5b95342fa337141b3b1ec85aac73229f (patch) | |
| tree | 0951671595086ca0720ba9512a857f4296c26a59 /newlib/libm/math | |
| parent | 14123c991b3b833e93a9dbb66c23beaf58c9ebab (diff) | |
| download | newlib-cf1ef2dc5b95342fa337141b3b1ec85aac73229f.zip newlib-cf1ef2dc5b95342fa337141b3b1ec85aac73229f.tar.gz newlib-cf1ef2dc5b95342fa337141b3b1ec85aac73229f.tar.bz2 | |
Fix error in powf for x close to 1 and large y
This patch fixes the error found by Paul Zimmermann (see
https://homepages.loria.fr/PZimmermann/papers/#accuracy) regarding x
close to 1 and rather large y (specifically he found the case
powf(0x1.ffffeep-1,-0x1.000002p+27) which returns +Inf instead of the
correct value). We found 2 more values for x which show the same faulty
behaviour, and all 3 are fixed with this patch. We have tested all
combinations for x in [+1.fffdfp-1, +1.00020p+0] and y in
[-1.000007p+27, -1.000002p+27] and [1.000002p+27,1.000007p+27].
Diffstat (limited to 'newlib/libm/math')
| -rw-r--r-- | newlib/libm/math/ef_pow.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/newlib/libm/math/ef_pow.c b/newlib/libm/math/ef_pow.c index e3579f0..07b225f 100644 --- a/newlib/libm/math/ef_pow.c +++ b/newlib/libm/math/ef_pow.c @@ -138,7 +138,7 @@ ivln2_l = 7.0526075433e-06; /* 0x36eca570 =1/ln2 tail*/ /* |y| is huge */ if(iy>0x4d000000) { /* if |y| > 2**27 */ /* over/underflow if x is not close to one */ - if(ix<0x3f7ffff8) return (hy<0)? __math_oflowf(0):__math_uflowf(0); + if(ix<0x3f7ffff4) return (hy<0)? __math_oflowf(0):__math_uflowf(0); if(ix>0x3f800007) return (hy>0)? __math_oflowf(0):__math_uflowf(0); /* now |1-x| is tiny <= 2**-20, suffice to compute log(x) by x-x^2/2+x^3/3-x^4/4 */ |