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/*
* ====================================================
* 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 <sys/cdefs.h>
__FBSDID("$FreeBSD$");
/*
* float version of __kernel_log(x). See k_log.c for details.
*/
static const float
/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
Lg1 = 0xaaaaaa.0p-24, /* 0.66666662693 */
Lg2 = 0xccce13.0p-25, /* 0.40000972152 */
Lg3 = 0x91e9ee.0p-25, /* 0.28498786688 */
Lg4 = 0xf89e26.0p-26; /* 0.24279078841 */
static inline float
__kernel_logf(float x)
{
float hfsq,f,s,z,R,w,t1,t2;
int32_t ix,i,j;
GET_FLOAT_WORD(ix,x);
f = x-(float)1.0;
if((0x007fffff&(0x8000+ix))<0xc000) { /* -2**-9 <= f < 2**-9 */
if(f==0.0f) return 0.0f;
return f*f*((float)0.33333333333333333*f-(float)0.5);
}
s = f/((float)2.0+f);
z = s*s;
ix &= 0x007fffff;
i = ix-(0x6147a<<3);
w = z*z;
j = (0x6b851<<3)-ix;
t1= w*(Lg2+w*Lg4);
t2= z*(Lg1+w*Lg3);
i |= j;
R = t2+t1;
if(i>0) {
hfsq=(float)0.5*f*f;
return s*(hfsq+R) - hfsq;
} else {
return s*(R-f);
}
}
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