e_log10f.c revision 2117
1/* e_log10f.c -- float version of e_log10.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 3 */ 4 5/* 6 * ==================================================== 7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 8 * 9 * Developed at SunPro, a Sun Microsystems, Inc. business. 10 * Permission to use, copy, modify, and distribute this 11 * software is freely granted, provided that this notice 12 * is preserved. 13 * ==================================================== 14 */ 15 16#ifndef lint 17static char rcsid[] = "$Id: e_log10f.c,v 1.2 1994/08/18 23:05:46 jtc Exp $"; 18#endif 19 20#include "math.h" 21#include "math_private.h" 22 23#ifdef __STDC__ 24static const float 25#else 26static float 27#endif 28one = 1.0, 29two25 = 3.3554432000e+07, /* 0x4c000000 */ 30ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */ 31log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 32log10_2lo = 7.9034151668e-07; /* 0x355427db */ 33 34#ifdef __STDC__ 35static const float zero = 0.0; 36#else 37static float zero = 0.0; 38#endif 39 40#ifdef __STDC__ 41 float __ieee754_log10f(float x) 42#else 43 float __ieee754_log10f(x) 44 float x; 45#endif 46{ 47 float y,z; 48 int32_t i,k,hx; 49 50 GET_FLOAT_WORD(hx,x); 51 52 k=0; 53 if (hx < 0x00800000) { /* x < 2**-126 */ 54 if ((hx&0x7fffffff)==0) 55 return -two25/zero; /* log(+-0)=-inf */ 56 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 57 k -= 25; x *= two25; /* subnormal number, scale up x */ 58 GET_FLOAT_WORD(hx,x); 59 } 60 if (hx >= 0x7f800000) return x+x; 61 k += (hx>>23)-127; 62 i = ((u_int32_t)k&0x80000000)>>31; 63 hx = (hx&0x007fffff)|((0x7f-i)<<23); 64 y = (float)(k+i); 65 SET_FLOAT_WORD(x,hx); 66 z = y*log10_2lo + ivln10*__ieee754_logf(x); 67 return z+y*log10_2hi; 68} 69