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
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