90 lines
2.4 KiB
C
90 lines
2.4 KiB
C
/* e_logf.c -- float version of e_log.c.
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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*/
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#include "cdefs-compat.h"
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//__FBSDID("$FreeBSD: src/lib/msun/src/e_logf.c,v 1.11 2008/03/29 16:37:59 das Exp $");
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#include <openlibm_math.h>
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#include "math_private.h"
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static const float
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ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
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ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */
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two25 = 3.355443200e+07, /* 0x4c000000 */
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/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
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Lg1 = 0xaaaaaa.0p-24, /* 0.66666662693 */
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Lg2 = 0xccce13.0p-25, /* 0.40000972152 */
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Lg3 = 0x91e9ee.0p-25, /* 0.28498786688 */
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Lg4 = 0xf89e26.0p-26; /* 0.24279078841 */
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static const float zero = 0.0;
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OLM_DLLEXPORT float
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__ieee754_logf(float x)
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{
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float hfsq,f,s,z,R,w,t1,t2,dk;
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int32_t k,ix,i,j;
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GET_FLOAT_WORD(ix,x);
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k=0;
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if (ix < 0x00800000) { /* x < 2**-126 */
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if ((ix&0x7fffffff)==0)
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return -two25/zero; /* log(+-0)=-inf */
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if (ix<0) return (x-x)/zero; /* log(-#) = NaN */
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k -= 25; x *= two25; /* subnormal number, scale up x */
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GET_FLOAT_WORD(ix,x);
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}
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if (ix >= 0x7f800000) return x+x;
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k += (ix>>23)-127;
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ix &= 0x007fffff;
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i = (ix+(0x95f64<<3))&0x800000;
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SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
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k += (i>>23);
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f = x-(float)1.0;
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if((0x007fffff&(0x8000+ix))<0xc000) { /* -2**-9 <= f < 2**-9 */
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if(f==zero) {
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if(k==0) {
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return zero;
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} else {
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dk=(float)k;
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return dk*ln2_hi+dk*ln2_lo;
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}
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}
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R = f*f*((float)0.5-(float)0.33333333333333333*f);
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if(k==0) return f-R; else {dk=(float)k;
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return dk*ln2_hi-((R-dk*ln2_lo)-f);}
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}
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s = f/((float)2.0+f);
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dk = (float)k;
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z = s*s;
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i = ix-(0x6147a<<3);
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w = z*z;
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j = (0x6b851<<3)-ix;
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t1= w*(Lg2+w*Lg4);
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t2= z*(Lg1+w*Lg3);
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i |= j;
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R = t2+t1;
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if(i>0) {
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hfsq=(float)0.5*f*f;
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if(k==0) return f-(hfsq-s*(hfsq+R)); else
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return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
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} else {
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if(k==0) return f-s*(f-R); else
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return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
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}
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}
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