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 14 static char rcsid[] = "$Id: s_logb.c,v 1.4 1994/03/03 17:04:41 jtc Exp $"; 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 <machine/endian.h> 25 26 #if BYTE_ORDER == LITTLE_ENDIAN 27 #define n0 1 28 #else 29 #define n0 0 30 #endif 31 32 #ifdef __STDC__ 33 double logb(double x) 34 #else 35 double logb(x) 36 double x; 37 #endif 38 { 39 int lx,ix; 40 ix = (*(n0+(int*)&x))&0x7fffffff; /* high |x| */ 41 lx = *(1-n0+(int*)&x); /* low x */ 42 if((ix|lx)==0) return -1.0/fabs(x); 43 if(ix>=0x7ff00000) return x*x; 44 if((ix>>=20)==0) /* IEEE 754 logb */ 45 return -1022.0; 46 else 47 return (double) (ix-1023); 48 } 49