1/*
2 * From: @(#)s_ilogb.c 5.1 93/09/24
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_ilogbl.c,v 1.1 2004/10/11 18:13:52 stefanf Exp $";
15#endif
16
17#include <float.h>
18#include <limits.h>
19#include <math.h>
20
21#include "fpmath.h"
22
23int
24ilogbl(long double x)
25{
26	union IEEEl2bits u;
27	unsigned long m;
28	int b;
29
30	u.e = x;
31	if (u.bits.exp == 0) {
32		if ((u.bits.manl | u.bits.manh) == 0)
33			return (FP_ILOGB0);
34		/* denormalized */
35		if (u.bits.manh == 0) {
36			m = 1lu << (LDBL_MANL_SIZE - 1);
37			for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
38				b++;
39		} else {
40			m = 1lu << (LDBL_MANH_SIZE - 1);
41			for (b = 0; !(u.bits.manh & m); m >>= 1)
42				b++;
43		}
44#ifdef LDBL_IMPLICIT_NBIT
45		b++;
46#endif
47		return (LDBL_MIN_EXP - b - 1);
48	} else if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)
49		return (u.bits.exp - LDBL_MAX_EXP + 1);
50	else if (u.bits.manl != 0 || u.bits.manh != 0)
51		return (FP_ILOGBNAN);
52	else
53		return (INT_MAX);
54}
55