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 #include <sys/cdefs.h> 14 #if defined(LIBM_SCCS) && !defined(lint) 15 __RCSID("$NetBSD: s_logb.c,v 1.12 2011/08/03 14:13:07 joerg Exp $"); 16 #endif 17 18 /* 19 * double logb(x) 20 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. 21 * Use ilogb instead. 22 */ 23 24 #include "math.h" 25 #include "math_private.h" 26 27 #ifndef __HAVE_LONG_DOUBLE 28 __strong_alias(logbl,logb) 29 #endif 30 31 double 32 logb(double x) 33 { 34 int32_t lx,ix; 35 EXTRACT_WORDS(ix,lx,x); 36 ix &= 0x7fffffff; /* high |x| */ 37 if((ix|lx)==0) return -1.0/fabs(x); 38 if(ix>=0x7ff00000) return x*x; 39 if((ix>>=20)==0) /* IEEE 754 logb */ 40 return -1022.0; 41 else 42 return (double) (ix-1023); 43 } 44