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 #if defined(LIBM_SCCS) && !defined(lint) 14 static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 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 "math_private.h" 25 26 int 27 ilogb(double x) 28 { 29 int32_t hx,lx,ix; 30 31 GET_HIGH_WORD(hx,x); 32 hx &= 0x7fffffff; 33 if(hx<0x00100000) { 34 GET_LOW_WORD(lx,x); 35 if((hx|lx)==0) 36 return 0x80000001; /* ilogb(0) = 0x80000001 */ 37 else /* subnormal x */ 38 if(hx==0) { 39 for (ix = -1043; lx>0; lx<<=1) ix -=1; 40 } else { 41 for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; 42 } 43 return ix; 44 } 45 else if (hx<0x7ff00000) return (hx>>20)-1023; 46 else return 0x7fffffff; 47 } 48