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Fix powf (close to -1, large) (bug 18647).

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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.
This commit is contained in:
Joseph Myers 2015-08-05 15:01:58 +00:00
parent 2aa6c8af26
commit cf36e5034f
5 changed files with 5661 additions and 2 deletions
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8
ChangeLog
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@ -1,3 +1,11 @@
2015-08-05 Joseph Myers <joseph@codesourcery.com>
[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.
2015-08-05 Adhemerval Zanella <adhemerval.zanella@linaro.org> 2015-08-05 Adhemerval Zanella <adhemerval.zanella@linaro.org>
* sysdeps/unix/sysv/linux/arm/mmap.c: Add file. * sysdeps/unix/sysv/linux/arm/mmap.c: Add file.

2
NEWS
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@ -8,7 +8,7 @@ using `glibc' in the "product" field.
Version 2.23 Version 2.23
* The following bugs are resolved with this release: * The following bugs are resolved with this release:
18265, 18525. 18265, 18525, 18647.
Version 2.22 Version 2.22

40
math/auto-libm-test-in
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@ -2361,6 +2361,46 @@ pow 0x0.ffffffffffffffffffffffffffff8p0 -0x1.23456789abcdef0123456789abcdp126
pow 0x1.0000000000000000000000000001p0 0x1.23456789abcdef0123456789abcdp125 pow 0x1.0000000000000000000000000001p0 0x1.23456789abcdef0123456789abcdp125
pow 0x1.0000000000000000000000000001p0 -0x1.23456789abcdef0123456789abcdp125 pow 0x1.0000000000000000000000000001p0 -0x1.23456789abcdef0123456789abcdp125
pow -0x0.ffffffp0 10
pow -0x0.ffffffp0 100
pow -0x0.ffffffp0 1000
pow -0x0.ffffffp0 0x1p24
pow -0x0.ffffffp0 0x1p30
pow -0x0.ffffffp0 0x1.234566p30
pow -0x0.ffffffp0 -10
pow -0x0.ffffffp0 -100
pow -0x0.ffffffp0 -1000
pow -0x0.ffffffp0 -0x1p24
pow -0x0.ffffffp0 -0x1p30
pow -0x0.ffffffp0 -0x1.234566p30
pow -0x1.000002p0 0x1p24
pow -0x1.000002p0 0x1.234566p29
pow -0x1.000002p0 -0x1.234566p29
pow -0x0.fffffffffffff8p0 0x1.23456789abcdfp62
pow -0x0.fffffffffffff8p0 -0x1.23456789abcdfp62
pow -0x1.0000000000001p0 0x1.23456789abcdfp61
pow -0x1.0000000000001p0 -0x1.23456789abcdfp61
pow -0x0.ffffffffffffffffp0 0x1.23456789abcdef0ep77
pow -0x0.ffffffffffffffffp0 -0x1.23456789abcdef0ep77
pow -0x1.0000000000000002p0 0x1.23456789abcdef0ep76
pow -0x1.0000000000000002p0 -0x1.23456789abcdef0ep76
pow -0x0.ffffffffffffffffffffffffffff8p0 0x1.23456789abcdef0123456789abcdp126
pow -0x0.ffffffffffffffffffffffffffff8p0 -0x1.23456789abcdef0123456789abcdp126
pow -0x1.0000000000000000000000000001p0 0x1.23456789abcdef0123456789abcdp125
pow -0x1.0000000000000000000000000001p0 -0x1.23456789abcdef0123456789abcdp125
pow 0x1.000002p0 0x1p30
pow -0x1.000002p0 0x1p30
pow 0x1.000002p0 max
pow -0x1.000002p0 max
pow 0x1.00000ep0 0x1p30
pow -0x1.00000ep0 0x1p30
pow 0x1.00000ep0 max
pow -0x1.00000ep0 max
pow 1e4932 0.75 pow 1e4932 0.75
pow 1e4928 0.75 pow 1e4928 0.75
pow 1e4924 0.75 pow 1e4924 0.75

5611
math/auto-libm-test-out
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2
sysdeps/ieee754/flt-32/e_powf.c
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@ -131,7 +131,7 @@ __ieee754_powf(float x, float y)
if(ix>0x3f800007) return (hy>0)? huge*huge:tiny*tiny; if(ix>0x3f800007) return (hy>0)? huge*huge:tiny*tiny;
/* now |1-x| is tiny <= 2**-20, suffice to compute /* now |1-x| is tiny <= 2**-20, suffice to compute
log(x) by x-x^2/2+x^3/3-x^4/4 */ 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)); w = (t*t)*((float)0.5-t*((float)0.333333333333-t*(float)0.25));
u = ivln2_h*t; /* ivln2_h has 16 sig. bits */ u = ivln2_h*t; /* ivln2_h has 16 sig. bits */
v = t*ivln2_l-w*ivln2; v = t*ivln2_l-w*ivln2;