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e_pow.c:

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Fixed pow(x, y) when x is very close to -1.0 and y is a very large odd
integer.  E.g., pow(-1.0 - pow(2.0, -52.0), 1.0 + pow(2.0, 52.0)) was
0.0 instead of being very close to -exp(1.0).

PR:		39236
Submitted by:	Stephen L Moshier <steve@moshier.net>

e_powf.c:
Apply the same patch although it is just cosmetic because odd integers
large enough to cause the problem are too large to be precisely represented
as floats.

MFC after:	1 week
This commit is contained in:
Bruce Evans 2002-06-17 15:28:59 +00:00
parent 93b99d6264
commit 3e2ec6ea88
2 changed files with 2 additions and 2 deletions
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2
lib/msun/src/e_pow.c
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@ -190,7 +190,7 @@ __ieee754_pow(double x, double y)
if(ix>0x3ff00000) 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)*(0.5-t*(0.3333333333333333333333-t*0.25));
u = ivln2_h*t; /* ivln2_h has 21 sig. bits */
v = t*ivln2_l-w*ivln2;

2
lib/msun/src/e_powf.c
View File

@ -130,7 +130,7 @@ __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;