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92 lines
2.2 KiB
C
92 lines
2.2 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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* adapted for log2 by Ulrich Drepper <drepper@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 "math.h"
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#include "math_private.h"
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#ifdef __STDC__
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static const float
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#else
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static float
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#endif
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ln2 = 0.69314718055994530942,
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two25 = 3.355443200e+07, /* 0x4c000000 */
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Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
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Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
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Lg3 = 2.8571429849e-01, /* 3E924925 */
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Lg4 = 2.2222198546e-01, /* 3E638E29 */
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Lg5 = 1.8183572590e-01, /* 3E3A3325 */
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Lg6 = 1.5313838422e-01, /* 3E1CD04F */
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Lg7 = 1.4798198640e-01; /* 3E178897 */
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#ifdef __STDC__
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static const float zero = 0.0;
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#else
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static float zero = 0.0;
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#endif
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#ifdef __STDC__
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float __log2f(float x)
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#else
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float __log2f(x)
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float x;
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#endif
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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/(x-x); /* log(+-0)=-inf */
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if (ix<0) return (x-x)/(x-x); /* 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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dk = (float)k;
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f = x-(float)1.0;
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if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
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if(f==zero) return dk;
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R = f*f*((float)0.5-(float)0.33333333333333333*f);
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return dk-(R-f)/ln2;
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}
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s = f/((float)2.0+f);
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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+w*Lg6));
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t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
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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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return dk-((hfsq-(s*(hfsq+R)))-f)/ln2;
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} else {
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return dk-((s*(f-R))-f)/ln2;
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}
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}
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weak_alias (__log2f, log2f)
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