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 
14 long double
logbl(long double x)15 logbl(long double x)
16 {
17 	union IEEEl2bits u;
18 	uint64_t m;
19 	int b;
20 
21 	u.e = x;
22 	if (u.bits.exp == 0) {
23 		if ((u.bits.manl | u.bits.manh) == 0) {	/* x == 0 */
24 			u.bits.sign = 1;
25 			return (1.0L / u.e);
26 		}
27 		/* denormalized */
28 #ifdef LDBL_MANL_SIZE
29 		if (u.bits.manh == 0) {
30 			m = 1llu << (LDBL_MANL_SIZE - 1);
31 			for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
32 				b++;
33 		} else
34 #endif
35                 {
36 			m = 1llu << (LDBL_MANH_SIZE - 1);
37 			for (b = 0; !(u.bits.manh & m); m >>= 1)
38 				b++;
39 		}
40 #ifdef LDBL_IMPLICIT_NBIT
41 		b++;
42 #endif
43 		return ((long double)(LDBL_MIN_EXP - b - 1));
44 	}
45 	if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)	/* normal */
46 		return ((long double)(u.bits.exp - LDBL_MAX_EXP + 1));
47 	else						/* +/- inf or nan */
48 		return (x * x);
49 }
50