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 __FBSDID("$FreeBSD$");
15 
16 /* ilogb(double x)
17  * return the binary exponent of non-zero x
18  * ilogb(0) = FP_ILOGB0
19  * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
20  * ilogb(inf) = INT_MAX (no signal is raised)
21  */
22 
23 #include <limits.h>
24 
25 #include "math.h"
26 #include "math_private.h"
27 
ilogb(double x)28 	int ilogb(double x)
29 {
30 	int32_t hx,lx,ix;
31 
32 	EXTRACT_WORDS(hx,lx,x);
33 	hx &= 0x7fffffff;
34 	if(hx<0x00100000) {
35 	    if((hx|lx)==0)
36 		return FP_ILOGB0;
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 if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
47 	else return INT_MAX;
48 }
49