e_logf.c revision 160151
12116Sjkh/* e_logf.c -- float version of e_log.c. 22116Sjkh * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 32116Sjkh */ 42116Sjkh 52116Sjkh/* 62116Sjkh * ==================================================== 72116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 82116Sjkh * 92116Sjkh * Developed at SunPro, a Sun Microsystems, Inc. business. 102116Sjkh * Permission to use, copy, modify, and distribute this 118870Srgrimes * software is freely granted, provided that this notice 122116Sjkh * is preserved. 132116Sjkh * ==================================================== 142116Sjkh */ 152116Sjkh 162116Sjkh#ifndef lint 1750476Speterstatic char rcsid[] = "$FreeBSD: head/lib/msun/src/e_logf.c 160151 2006-07-07 04:33:08Z bde $"; 182116Sjkh#endif 192116Sjkh 202116Sjkh#include "math.h" 212116Sjkh#include "math_private.h" 222116Sjkh 232116Sjkhstatic const float 242116Sjkhln2_hi = 6.9313812256e-01, /* 0x3f317180 */ 252116Sjkhln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */ 262116Sjkhtwo25 = 3.355443200e+07, /* 0x4c000000 */ 27152335Sbde/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */ 28152335SbdeLg1 = 0xaaaaaa.0p-24, /* 0.66666662693 */ 29152335SbdeLg2 = 0xccce13.0p-25, /* 0.40000972152 */ 30152335SbdeLg3 = 0x91e9ee.0p-25, /* 0.28498786688 */ 31152335SbdeLg4 = 0xf89e26.0p-26; /* 0.24279078841 */ 322116Sjkh 332116Sjkhstatic const float zero = 0.0; 342116Sjkh 3597413Salfredfloat 3697413Salfred__ieee754_logf(float x) 372116Sjkh{ 382116Sjkh float hfsq,f,s,z,R,w,t1,t2,dk; 392116Sjkh int32_t k,ix,i,j; 402116Sjkh 412116Sjkh GET_FLOAT_WORD(ix,x); 422116Sjkh 432116Sjkh k=0; 442116Sjkh if (ix < 0x00800000) { /* x < 2**-126 */ 458870Srgrimes if ((ix&0x7fffffff)==0) 462116Sjkh return -two25/zero; /* log(+-0)=-inf */ 472116Sjkh if (ix<0) return (x-x)/zero; /* log(-#) = NaN */ 482116Sjkh k -= 25; x *= two25; /* subnormal number, scale up x */ 492116Sjkh GET_FLOAT_WORD(ix,x); 508870Srgrimes } 512116Sjkh if (ix >= 0x7f800000) return x+x; 522116Sjkh k += (ix>>23)-127; 532116Sjkh ix &= 0x007fffff; 542116Sjkh i = (ix+(0x95f64<<3))&0x800000; 552116Sjkh SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */ 562116Sjkh k += (i>>23); 572116Sjkh f = x-(float)1.0; 58160151Sbde if((0x007fffff&(0x8000+ix))<0xc000) { /* -2**-9 <= f < 2**-9 */ 592116Sjkh if(f==zero) if(k==0) return zero; else {dk=(float)k; 602116Sjkh return dk*ln2_hi+dk*ln2_lo;} 612116Sjkh R = f*f*((float)0.5-(float)0.33333333333333333*f); 622116Sjkh if(k==0) return f-R; else {dk=(float)k; 632116Sjkh return dk*ln2_hi-((R-dk*ln2_lo)-f);} 642116Sjkh } 658870Srgrimes s = f/((float)2.0+f); 662116Sjkh dk = (float)k; 672116Sjkh z = s*s; 682116Sjkh i = ix-(0x6147a<<3); 692116Sjkh w = z*z; 702116Sjkh j = (0x6b851<<3)-ix; 71152335Sbde t1= w*(Lg2+w*Lg4); 72152335Sbde t2= z*(Lg1+w*Lg3); 732116Sjkh i |= j; 742116Sjkh R = t2+t1; 752116Sjkh if(i>0) { 762116Sjkh hfsq=(float)0.5*f*f; 772116Sjkh if(k==0) return f-(hfsq-s*(hfsq+R)); else 782116Sjkh return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f); 792116Sjkh } else { 802116Sjkh if(k==0) return f-s*(f-R); else 812116Sjkh return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f); 822116Sjkh } 832116Sjkh} 84