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 1.14 2013/02/09 22:56:00 matt 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 #ifndef __HAVE_LONG_DOUBLE 28 __strong_alias(ilogbl,ilogb) 29 #endif 30 31 int 32 ilogb(double x) 33 { 34 int32_t hx,lx,ix; 35 36 GET_HIGH_WORD(hx,x); 37 hx &= 0x7fffffff; 38 if(hx<0x00100000) { 39 GET_LOW_WORD(lx,x); 40 if((hx|lx)==0) 41 return FP_ILOGB0; /* ilogb(0) = 0x80000001 */ 42 else /* subnormal x */ 43 if(hx==0) { 44 for (ix = -1043; lx>0; lx<<=1) ix -=1; 45 } else { 46 for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; 47 } 48 return ix; 49 } 50 else if (hx<0x7ff00000) return (hx>>20)-1023; 51 else return FP_ILOGBNAN; /* inf too */ 52 } 53