s_logb.c revision 117912
195821Sphk/* @(#)s_logb.c 5.1 93/09/24 */ 258377Sphk/* 358377Sphk * ==================================================== 458377Sphk * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 558377Sphk * 658377Sphk * Developed at SunPro, a Sun Microsystems, Inc. business. 758377Sphk * Permission to use, copy, modify, and distribute this 8227723Slstewart * software is freely granted, provided that this notice 9227723Slstewart * is preserved. 10227723Slstewart * ==================================================== 11227723Slstewart */ 12227723Slstewart 13227723Slstewart#ifndef lint 141541Srgrimesstatic char rcsid[] = "$FreeBSD: head/lib/msun/src/s_logb.c 117912 2003-07-23 04:53:47Z peter $"; 151541Srgrimes#endif 16116182Sobrien 17116182Sobrien/* 18116182Sobrien * double logb(x) 19237433Skib * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 2044666Sphk * Use ilogb instead. 21227723Slstewart */ 2244666Sphk 231541Srgrimes#include "math.h" 2458377Sphk#include "math_private.h" 25227723Slstewart 26227723Slstewartdouble 27227723Slstewartlogb(double x) 28227723Slstewart{ 2958377Sphk int32_t lx,ix; 30124812Sphk EXTRACT_WORDS(ix,lx,x); 311541Srgrimes ix &= 0x7fffffff; /* high |x| */ 32227723Slstewart if((ix|lx)==0) return -1.0/fabs(x); 3395976Sphk if(ix>=0x7ff00000) return x*x; 34237433Skib if((ix>>=20)==0) /* IEEE 754 logb */ 3595821Sphk return -1022.0; 362858Swollman else 37237433Skib return (double) (ix-1023); 381541Srgrimes} 3940609Sphk