1 /* e_log10f.c -- float version of e_log10.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) 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 17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_log10f.c,v 1.8 2002/05/28 18:15:04 alfred Exp $"; 18 #endif 19 20 #include "math.h" 21 #include "math_private.h" 22 23 static const float 24 two25 = 3.3554432000e+07, /* 0x4c000000 */ 25 ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */ 26 log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 27 log10_2lo = 7.9034151668e-07; /* 0x355427db */ 28 29 static const float zero = 0.0; 30 31 float 32 __ieee754_log10f(float x) 33 { 34 float y,z; 35 int32_t i,k,hx; 36 37 GET_FLOAT_WORD(hx,x); 38 39 k=0; 40 if (hx < 0x00800000) { /* x < 2**-126 */ 41 if ((hx&0x7fffffff)==0) 42 return -two25/zero; /* log(+-0)=-inf */ 43 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 44 k -= 25; x *= two25; /* subnormal number, scale up x */ 45 GET_FLOAT_WORD(hx,x); 46 } 47 if (hx >= 0x7f800000) return x+x; 48 k += (hx>>23)-127; 49 i = ((u_int32_t)k&0x80000000)>>31; 50 hx = (hx&0x007fffff)|((0x7f-i)<<23); 51 y = (float)(k+i); 52 SET_FLOAT_WORD(x,hx); 53 z = y*log10_2lo + ivln10*__ieee754_logf(x); 54 return z+y*log10_2hi; 55 } 56
