122 lines
3.0 KiB
C
122 lines
3.0 KiB
C
/* sf_log1p.c -- float version of s_log1p.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 "fdlibm.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_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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Lp1 = 6.6666668653e-01, /* 3F2AAAAB */
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Lp2 = 4.0000000596e-01, /* 3ECCCCCD */
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Lp3 = 2.8571429849e-01, /* 3E924925 */
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Lp4 = 2.2222198546e-01, /* 3E638E29 */
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Lp5 = 1.8183572590e-01, /* 3E3A3325 */
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Lp6 = 1.5313838422e-01, /* 3E1CD04F */
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Lp7 = 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 log1pf(float x)
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#else
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float log1pf(x)
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float x;
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#endif
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{
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float hfsq,f,c,s,z,R,u;
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__int32_t k,hx,hu,ax;
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GET_FLOAT_WORD(hx,x);
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ax = hx&0x7fffffff;
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k = 1;
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if (!FLT_UWORD_IS_FINITE(hx)) return x+x;
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if (hx < 0x3ed413d7) { /* x < 0.41422 */
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if(ax>=0x3f800000) { /* x <= -1.0 */
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if(x==(float)-1.0) return -two25/zero; /* log1p(-1)=+inf */
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else return (x-x)/(x-x); /* log1p(x<-1)=NaN */
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}
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if(ax<0x31000000) { /* |x| < 2**-29 */
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if(two25+x>zero /* raise inexact */
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&&ax<0x24800000) /* |x| < 2**-54 */
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return x;
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else
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return x - x*x*(float)0.5;
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}
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if(hx>0||hx<=((__int32_t)0xbe95f61f)) {
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k=0;f=x;hu=1;} /* -0.2929<x<0.41422 */
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}
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if(k!=0) {
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if(hx<0x5a000000) {
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u = (float)1.0+x;
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GET_FLOAT_WORD(hu,u);
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k = (hu>>23)-127;
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/* correction term */
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c = (k>0)? (float)1.0-(u-x):x-(u-(float)1.0);
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c /= u;
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} else {
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u = x;
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GET_FLOAT_WORD(hu,u);
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k = (hu>>23)-127;
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c = 0;
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}
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hu &= 0x007fffff;
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if(hu<0x3504f7) {
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SET_FLOAT_WORD(u,hu|0x3f800000);/* normalize u */
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} else {
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k += 1;
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SET_FLOAT_WORD(u,hu|0x3f000000); /* normalize u/2 */
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hu = (0x00800000-hu)>>2;
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}
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f = u-(float)1.0;
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}
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hfsq=(float)0.5*f*f;
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if(hu==0) { /* |f| < 2**-20 */
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if(f==zero) { if(k==0) return zero;
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else {c += k*ln2_lo; return k*ln2_hi+c;}}
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R = hfsq*((float)1.0-(float)0.66666666666666666*f);
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if(k==0) return f-R; else
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return k*ln2_hi-((R-(k*ln2_lo+c))-f);
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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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R = z*(Lp1+z*(Lp2+z*(Lp3+z*(Lp4+z*(Lp5+z*(Lp6+z*Lp7))))));
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if(k==0) return f-(hfsq-s*(hfsq+R)); else
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return k*ln2_hi-((hfsq-(s*(hfsq+R)+(k*ln2_lo+c)))-f);
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}
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#ifdef _DOUBLE_IS_32BITS
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#ifdef __STDC__
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double log1p(double x)
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#else
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double log1p(x)
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double x;
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#endif
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{
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return (double) log1pf((float) x);
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}
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#endif /* defined(_DOUBLE_IS_32BITS) */
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