s_logb.c revision 153049
12116Sjkh/* @(#)s_logb.c 5.1 93/09/24 */ 22116Sjkh/* 32116Sjkh * ==================================================== 42116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 52116Sjkh * 62116Sjkh * Developed at SunPro, a Sun Microsystems, Inc. business. 72116Sjkh * Permission to use, copy, modify, and distribute this 88870Srgrimes * software is freely granted, provided that this notice 92116Sjkh * is preserved. 102116Sjkh * ==================================================== 112116Sjkh */ 122116Sjkh 132116Sjkh#ifndef lint 1450476Speterstatic char rcsid[] = "$FreeBSD: head/lib/msun/src/s_logb.c 153049 2005-12-03 11:57:19Z bde $"; 152116Sjkh#endif 162116Sjkh 172116Sjkh/* 182116Sjkh * double logb(x) 192116Sjkh * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 202116Sjkh * Use ilogb instead. 212116Sjkh */ 222116Sjkh 232116Sjkh#include "math.h" 242116Sjkh#include "math_private.h" 252116Sjkh 26153049Sbdestatic const double 27153049Sbdetwo54 = 1.80143985094819840000e+16; /* 43500000 00000000 */ 28153049Sbde 2997413Salfreddouble 30117912Speterlogb(double x) 312116Sjkh{ 322116Sjkh int32_t lx,ix; 332116Sjkh EXTRACT_WORDS(ix,lx,x); 342116Sjkh ix &= 0x7fffffff; /* high |x| */ 352116Sjkh if((ix|lx)==0) return -1.0/fabs(x); 362116Sjkh if(ix>=0x7ff00000) return x*x; 37153049Sbde if(ix<0x00100000) { 38153049Sbde x *= two54; /* convert subnormal x to normal */ 39153049Sbde GET_FLOAT_WORD(ix,x); 40153049Sbde ix &= 0x7fffffff; 41153049Sbde return (float) ((ix>>20)-1023-54); 42153049Sbde } else 43153049Sbde return (double) ((ix>>20)-1023); 442116Sjkh} 45