1 /* @(#)s_ilogb.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_ilogb.c,v 1.4 1994/03/03 17:04:38 jtc Exp $"; 15 #endif 16 17 /* ilogb(double x) 18 * return the binary exponent of non-zero x 19 * ilogb(0) = 0x80000001 20 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised) 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 int ilogb(double x) 34 #else 35 int ilogb(x) 36 double x; 37 #endif 38 { 39 int hx,lx,ix; 40 41 hx = (*(n0+(unsigned*)&x))&0x7fffffff; /* high word of x */ 42 if(hx<0x00100000) { 43 lx = *(1-n0+(int*)&x); 44 if((hx|lx)==0) 45 return 0x80000001; /* ilogb(0) = 0x80000001 */ 46 else /* subnormal x */ 47 if(hx==0) { 48 for (ix = -1043; lx>0; lx<<=1) ix -=1; 49 } else { 50 for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; 51 } 52 return ix; 53 } 54 else if (hx<0x7ff00000) return (hx>>20)-1023; 55 else return 0x7fffffff; 56 } 57