RTAI API: base/math/s_ilogb.c Source File

00001 /* @(#)s_ilogb.c 5.1 93/09/24 */
00002 /*
00003  * ====================================================
00004  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
00005  *
00006  * Developed at SunPro, a Sun Microsystems, Inc. business.
00007  * Permission to use, copy, modify, and distribute this
00008  * software is freely granted, provided that this notice 
00009  * is preserved.
00010  * ====================================================
00011  */
00012 
00013 #if defined(LIBM_SCCS) && !defined(lint)
00014 static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";
00015 #endif
00016 
00017 /* ilogb(double x)
00018  * return the binary exponent of non-zero x
00019  * ilogb(0) = 0x80000001
00020  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
00021  */
00022 
00023 #include "math.h"
00024 #include "mathP.h"
00025 
00026 #ifdef __STDC__
00027     int ilogb(double x)
00028 #else
00029     int ilogb(x)
00030     double x;
00031 #endif
00032 {
00033     int32_t hx,lx,ix;
00034 
00035     GET_HIGH_WORD(hx,x);
00036     hx &= 0x7fffffff;
00037     if(hx<0x00100000) {
00038         GET_LOW_WORD(lx,x);
00039         if((hx|lx)==0) 
00040         return 0x80000001;  /* ilogb(0) = 0x80000001 */
00041         else            /* subnormal x */
00042         if(hx==0) {
00043             for (ix = -1043; lx>0; lx<<=1) ix -=1;
00044         } else {
00045             for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
00046         }
00047         return ix;
00048     }
00049     else if (hx<0x7ff00000) return (hx>>20)-1023;
00050     else return 0x7fffffff;
00051 }