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authorJoseph Myers <joseph@codesourcery.com>2015-08-05 15:01:58 +0000
committerJoseph Myers <joseph@codesourcery.com>2015-08-05 15:01:58 +0000
commitcf36e5034fa8ed5d44036bce09a55a7f00d19252 (patch)
tree9fca061d81056a70793ebee9bf828b4e5b97f724 /sysdeps
parent2aa6c8af26e65695e9daf382a6e508574a30cdf2 (diff)
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Fix powf (close to -1, large) (bug 18647).
The flt-32 implementation of powf wrongly uses x-1 instead of |x|-1
when computing log (x) for the case where |x| is close to 1 and y is
large.  This patch fixes the logic accordingly.  Relevant tests
existed for x close to 1, and corresponding tests are added for x
close to -1, as well as for some new variant cases.

Tested for x86_64 and x86.

	[BZ #18647]
	* sysdeps/ieee754/flt-32/e_powf.c (__ieee754_powf): For large y
	and |x| close to 1, use absolute value of x when computing log.
	* math/auto-libm-test-in: Add more tests of pow.
	* math/auto-libm-test-out: Regenerated.
Diffstat (limited to 'sysdeps')
-rw-r--r--sysdeps/ieee754/flt-32/e_powf.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/sysdeps/ieee754/flt-32/e_powf.c b/sysdeps/ieee754/flt-32/e_powf.c
index 12c408f93c..8e8d918456 100644
--- a/sysdeps/ieee754/flt-32/e_powf.c
+++ b/sysdeps/ieee754/flt-32/e_powf.c
@@ -131,7 +131,7 @@ __ieee754_powf(float x, float y)
 	    if(ix>0x3f800007) return (hy>0)? huge*huge:tiny*tiny;
 	/* now |1-x| is tiny <= 2**-20, suffice to compute
 	   log(x) by x-x^2/2+x^3/3-x^4/4 */
-	    t = x-1;		/* t has 20 trailing zeros */
+	    t = ax-1;		/* t has 20 trailing zeros */
 	    w = (t*t)*((float)0.5-t*((float)0.333333333333-t*(float)0.25));
 	    u = ivln2_h*t;	/* ivln2_h has 16 sig. bits */
 	    v = t*ivln2_l-w*ivln2;