e_log10f.c revision 219361
1/* 2 * ==================================================== 3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 4 * 5 * Developed at SunPro, a Sun Microsystems, Inc. business. 6 * Permission to use, copy, modify, and distribute this 7 * software is freely granted, provided that this notice 8 * is preserved. 9 * ==================================================== 10 */ 11 12#include <sys/cdefs.h> 13__FBSDID("$FreeBSD: head/lib/msun/src/e_log10f.c 219361 2011-03-07 03:12:08Z das $"); 14 15/* 16 * Return the base 10 logarithm of x. See k_log.c for details on the algorithm. 17 */ 18 19#include "math.h" 20#include "math_private.h" 21#include "k_logf.h" 22 23static const float 24two25 = 3.3554432000e+07, /* 0x4c000000 */ 25ivln10hi = 4.3432617188e-01, /* 0x3ede6000 */ 26ivln10lo = -3.1689971365e-05, /* 0xb804ead9 */ 27log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 28log10_2lo = 7.9034151668e-07; /* 0x355427db */ 29 30static const float zero = 0.0; 31 32float 33__ieee754_log10f(float x) 34{ 35 float f,hi,lo,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 hx &= 0x007fffff; 51 i = (hx+(0x4afb0d))&0x800000; 52 SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */ 53 k += (i>>23); 54 y = (float)k; 55 f = __kernel_logf(x); 56 x = x - (float)1.0; 57 GET_FLOAT_WORD(hx,x); 58 SET_FLOAT_WORD(hi,hx&0xfffff000); 59 lo = x - hi; 60 z = y*log10_2lo + (x+f)*ivln10lo + (lo+f)*ivln10hi + hi*ivln10hi; 61 return z+y*log10_2hi; 62} 63