s_logbl.c revision 324006 
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#include <sys/cdefs.h>
14__FBSDID("$FreeBSD: stable/11/lib/msun/src/s_logbl.c 324006 2017-09-26 09:01:56Z dim $");
15
16#include <float.h>
17#include <limits.h>
18#include <math.h>
19
20#include "fpmath.h"
21
22long double
23logbl(long double x)
24{
25	union IEEEl2bits u;
26	unsigned long m;
27	int b;
28
29	u.e = x;
30	if (u.bits.exp == 0) {
31		if ((u.bits.manl | u.bits.manh) == 0) {	/* x == 0 */
32			u.bits.sign = 1;
33			return (1.0L / u.e);
34		}
35		/* denormalized */
36		if (u.bits.manh == 0) {
37			m = 1lu << (LDBL_MANL_SIZE - 1);
38			for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
39				b++;
40		} else {
41			m = 1lu << (LDBL_MANH_SIZE - 1);
42			for (b = 0; !(u.bits.manh & m); m >>= 1)
43				b++;
44		}
45#ifdef LDBL_IMPLICIT_NBIT
46		b++;
47#endif
48		return ((long double)(LDBL_MIN_EXP - b - 1));
49	}
50	if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)	/* normal */
51		return ((long double)(u.bits.exp - LDBL_MAX_EXP + 1));
52	else						/* +/- inf or nan */
53		return (x * x);
54}
55