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[] = "$FreeBSD$";
15#endif
16
17#include <float.h>
18#include <limits.h>
19#include <math.h>
20
21#include "fpmath.h"
22
23long double
24logbl(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) {	/* x == 0 */
33			u.bits.sign = 1;
34			return (1.0L / u.e);
35		}
36		/* denormalized */
37		if (u.bits.manh == 0) {
38			m = 1lu << (LDBL_MANL_SIZE - 1);
39			for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
40				b++;
41		} else {
42			m = 1lu << (LDBL_MANH_SIZE - 1);
43			for (b = 0; !(u.bits.manh & m); m >>= 1)
44				b++;
45		}
46#ifdef LDBL_IMPLICIT_NBIT
47		b++;
48#endif
49		return ((long double)(LDBL_MIN_EXP - b - 1));
50	}
51	if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)	/* normal */
52		return ((long double)(u.bits.exp - LDBL_MAX_EXP + 1));
53	else						/* +/- inf or nan */
54		return (x * x);
55}
56