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 #include <sys/cdefs.h> 14 #if defined(LIBM_SCCS) && !defined(lint) 15 __RCSID("$NetBSD: s_ilogb.c,v 1.12 2002/05/26 22:01:56 wiz Exp $"); 16 #endif 17 18 /* ilogb(double x) 19 * return the binary exponent of non-zero x 20 * ilogb(0) = 0x80000001 21 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised) 22 */ 23 24 #include "math.h" 25 #include "math_private.h" 26 27 int 28 ilogb(double x) 29 { 30 int32_t hx,lx,ix; 31 32 GET_HIGH_WORD(hx,x); 33 hx &= 0x7fffffff; 34 if(hx<0x00100000) { 35 GET_LOW_WORD(lx,x); 36 if((hx|lx)==0) 37 return 0x80000001; /* ilogb(0) = 0x80000001 */ 38 else /* subnormal x */ 39 if(hx==0) { 40 for (ix = -1043; lx>0; lx<<=1) ix -=1; 41 } else { 42 for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; 43 } 44 return ix; 45 } 46 else if (hx<0x7ff00000) return (hx>>20)-1023; 47 else return 0x7fffffff; 48 } 49