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
14static 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}
50