s_ilogb.c (1240B)
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[] = "$FreeBSD: src/lib/msun/src/s_ilogb.c,v 1.9 2004/10/09 17:14:28 stefanf Exp $"; 15 #endif 16 17 /* ilogb(double x) 18 * return the binary exponent of non-zero x 19 * ilogb(0) = FP_ILOGB0 20 * ilogb(NaN) = FP_ILOGBNAN (no signal is raised) 21 * ilogb(inf) = INT_MAX (no signal is raised) 22 */ 23 24 #include <limits.h> 25 26 #include "math.h" 27 #include "math_private.h" 28 29 int ilogb(double x) 30 { 31 int32_t hx,lx,ix; 32 33 EXTRACT_WORDS(hx,lx,x); 34 hx &= 0x7fffffff; 35 if(hx<0x00100000) { 36 if((hx|lx)==0) 37 return FP_ILOGB0; 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 if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN; 48 else return INT_MAX; 49 }