e_log10f.c revision 8870
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 1995/04/07 23:23:23 bde 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 28two25 = 3.3554432000e+07, /* 0x4c000000 */ 29ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */ 30log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 31log10_2lo = 7.9034151668e-07; /* 0x355427db */ 32 33#ifdef __STDC__ 34static const float zero = 0.0; 35#else 36static float zero = 0.0; 37#endif 38 39#ifdef __STDC__ 40 float __ieee754_log10f(float x) 41#else 42 float __ieee754_log10f(x) 43 float x; 44#endif 45{ 46 float y,z; 47 int32_t i,k,hx; 48 49 GET_FLOAT_WORD(hx,x); 50 51 k=0; 52 if (hx < 0x00800000) { /* x < 2**-126 */ 53 if ((hx&0x7fffffff)==0) 54 return -two25/zero; /* log(+-0)=-inf */ 55 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 56 k -= 25; x *= two25; /* subnormal number, scale up x */ 57 GET_FLOAT_WORD(hx,x); 58 } 59 if (hx >= 0x7f800000) return x+x; 60 k += (hx>>23)-127; 61 i = ((u_int32_t)k&0x80000000)>>31; 62 hx = (hx&0x007fffff)|((0x7f-i)<<23); 63 y = (float)(k+i); 64 SET_FLOAT_WORD(x,hx); 65 z = y*log10_2lo + ivln10*__ieee754_logf(x); 66 return z+y*log10_2hi; 67} 68