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 #include <sys/cdefs.h> 17 #if defined(LIBM_SCCS) && !defined(lint) 18 __RCSID("$NetBSD: e_log10f.c,v 1.8 2002/05/26 22:01:51 wiz Exp $"); 19 #endif 20 21 #include "math.h" 22 #include "math_private.h" 23 24 static const float 25 two25 = 3.3554432000e+07, /* 0x4c000000 */ 26 ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */ 27 log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 28 log10_2lo = 7.9034151668e-07; /* 0x355427db */ 29 30 static const float zero = 0.0; 31 32 float 33 __ieee754_log10f(float x) 34 { 35 float y,z; 36 int32_t i,k,hx; 37 38 GET_FLOAT_WORD(hx,x); 39 40 k=0; 41 if (hx < 0x00800000) { /* x < 2**-126 */ 42 if ((hx&0x7fffffff)==0) 43 return -two25/zero; /* log(+-0)=-inf */ 44 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 45 k -= 25; x *= two25; /* subnormal number, scale up x */ 46 GET_FLOAT_WORD(hx,x); 47 } 48 if (hx >= 0x7f800000) return x+x; 49 k += (hx>>23)-127; 50 i = ((u_int32_t)k&0x80000000)>>31; 51 hx = (hx&0x007fffff)|((0x7f-i)<<23); 52 y = (float)(k+i); 53 SET_FLOAT_WORD(x,hx); 54 z = y*log10_2lo + ivln10*__ieee754_logf(x); 55 return z+y*log10_2hi; 56 } 57