e_log2f.c revision 216211
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_log2f.c 216211 2010-12-05 22:11:22Z das $"); 14 15#include "math.h" 16#include "math_private.h" 17#include "k_logf.h" 18 19static const float 20two25 = 3.3554432000e+07, /* 0x4c000000 */ 21ivln2hi = 0x1.716p+0f, 22ivln2lo = -0x1.7135a8fa03d11p-13; 23 24static const float zero = 0.0; 25 26float 27__ieee754_log2f(float x) 28{ 29 float f,hi,lo; 30 int32_t i,k,hx; 31 32 GET_FLOAT_WORD(hx,x); 33 34 k=0; 35 if (hx < 0x00800000) { /* x < 2**-126 */ 36 if ((hx&0x7fffffff)==0) 37 return -two25/zero; /* log(+-0)=-inf */ 38 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 39 k -= 25; x *= two25; /* subnormal number, scale up x */ 40 GET_FLOAT_WORD(hx,x); 41 } 42 if (hx >= 0x7f800000) return x+x; 43 k += (hx>>23)-127; 44 hx &= 0x007fffff; 45 i = (hx+(0x4afb0d))&0x800000; 46 SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */ 47 k += (i>>23); 48 f = __kernel_logf(x); 49 x = x - 1; 50 GET_FLOAT_WORD(hx,x); 51 SET_FLOAT_WORD(hi,hx&0xfffff000); 52 lo = x - hi; 53 return (x+f)*ivln2lo + (lo+f)*ivln2hi + hi*ivln2hi + k; 54} 55