mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-26 20:51:11 +00:00
81 lines
2.1 KiB
C
81 lines
2.1 KiB
C
/* e_logf.c -- float version of e_log.c.
|
|
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
|
|
* adapted for log2 by Ulrich Drepper <drepper@cygnus.com>
|
|
*/
|
|
|
|
/*
|
|
* ====================================================
|
|
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
|
|
*
|
|
* Developed at SunPro, a Sun Microsystems, Inc. business.
|
|
* Permission to use, copy, modify, and distribute this
|
|
* software is freely granted, provided that this notice
|
|
* is preserved.
|
|
* ====================================================
|
|
*/
|
|
|
|
|
|
#include <math.h>
|
|
#include <math_private.h>
|
|
|
|
static const float
|
|
ln2 = 0.69314718055994530942,
|
|
two25 = 3.355443200e+07, /* 0x4c000000 */
|
|
Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
|
|
Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
|
|
Lg3 = 2.8571429849e-01, /* 3E924925 */
|
|
Lg4 = 2.2222198546e-01, /* 3E638E29 */
|
|
Lg5 = 1.8183572590e-01, /* 3E3A3325 */
|
|
Lg6 = 1.5313838422e-01, /* 3E1CD04F */
|
|
Lg7 = 1.4798198640e-01; /* 3E178897 */
|
|
|
|
static const float zero = 0.0;
|
|
|
|
float
|
|
__ieee754_log2f(float x)
|
|
{
|
|
float hfsq,f,s,z,R,w,t1,t2,dk;
|
|
int32_t k,ix,i,j;
|
|
|
|
GET_FLOAT_WORD(ix,x);
|
|
|
|
k=0;
|
|
if (ix < 0x00800000) { /* x < 2**-126 */
|
|
if (__builtin_expect((ix&0x7fffffff)==0, 0))
|
|
return -two25/(x-x); /* log(+-0)=-inf */
|
|
if (__builtin_expect(ix<0, 0))
|
|
return (x-x)/(x-x); /* log(-#) = NaN */
|
|
k -= 25; x *= two25; /* subnormal number, scale up x */
|
|
GET_FLOAT_WORD(ix,x);
|
|
}
|
|
if (__builtin_expect(ix >= 0x7f800000, 0)) return x+x;
|
|
k += (ix>>23)-127;
|
|
ix &= 0x007fffff;
|
|
i = (ix+(0x95f64<<3))&0x800000;
|
|
SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
|
|
k += (i>>23);
|
|
dk = (float)k;
|
|
f = x-(float)1.0;
|
|
if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
|
|
if(f==zero) return dk;
|
|
R = f*f*((float)0.5-(float)0.33333333333333333*f);
|
|
return dk-(R-f)/ln2;
|
|
}
|
|
s = f/((float)2.0+f);
|
|
z = s*s;
|
|
i = ix-(0x6147a<<3);
|
|
w = z*z;
|
|
j = (0x6b851<<3)-ix;
|
|
t1= w*(Lg2+w*(Lg4+w*Lg6));
|
|
t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
|
|
i |= j;
|
|
R = t2+t1;
|
|
if(i>0) {
|
|
hfsq=(float)0.5*f*f;
|
|
return dk-((hfsq-(s*(hfsq+R)))-f)/ln2;
|
|
} else {
|
|
return dk-((s*(f-R))-f)/ln2;
|
|
}
|
|
}
|
|
strong_alias (__ieee754_log2f, __log2f_finite)
|