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("$FreeBSD$");
15 
16 #include <float.h>
17 #include <limits.h>
18 #include <math.h>
19 
20 #include "fpmath.h"
21 
22 int
ilogbl(long double x)23 ilogbl(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)
32 			return (FP_ILOGB0);
33 		/* denormalized */
34 		if (u.bits.manh == 0) {
35 			m = 1lu << (LDBL_MANL_SIZE - 1);
36 			for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
37 				b++;
38 		} else {
39 			m = 1lu << (LDBL_MANH_SIZE - 1);
40 			for (b = 0; !(u.bits.manh & m); m >>= 1)
41 				b++;
42 		}
43 #ifdef LDBL_IMPLICIT_NBIT
44 		b++;
45 #endif
46 		return (LDBL_MIN_EXP - b - 1);
47 	} else if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)
48 		return (u.bits.exp - LDBL_MAX_EXP + 1);
49 	else if (u.bits.manl != 0 || u.bits.manh != 0)
50 		return (FP_ILOGBNAN);
51 	else
52 		return (INT_MAX);
53 }
54