s_logb.c revision 117912
1/* @(#)s_logb.c 5.1 93/09/24 */ 2/* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13#ifndef lint 14static char rcsid[] = "$FreeBSD: head/lib/msun/src/s_logb.c 117912 2003-07-23 04:53:47Z peter $"; 15#endif 16 17/* 18 * double logb(x) 19 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 20 * Use ilogb instead. 21 */ 22 23#include "math.h" 24#include "math_private.h" 25 26double 27logb(double x) 28{ 29 int32_t lx,ix; 30 EXTRACT_WORDS(ix,lx,x); 31 ix &= 0x7fffffff; /* high |x| */ 32 if((ix|lx)==0) return -1.0/fabs(x); 33 if(ix>=0x7ff00000) return x*x; 34 if((ix>>=20)==0) /* IEEE 754 logb */ 35 return -1022.0; 36 else 37 return (double) (ix-1023); 38} 39