1 /* $NetBSD: s_logbl.c,v 1.1 2011/08/03 14:13:07 joerg Exp $ */
2
3 /*-
4 * Copyright (c) 2011 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Joerg Sonnenberger.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32 #include <sys/cdefs.h>
33 __RCSID("$NetBSD: s_logbl.c,v 1.1 2011/08/03 14:13:07 joerg Exp $");
34
35 #include "namespace.h"
36
37 #include <float.h>
38 #include <math.h>
39 #include <machine/ieee.h>
40
41 #ifdef __HAVE_LONG_DOUBLE
42
43 #if LDBL_MANT_DIG == 64
44 #define FROM_UNDERFLOW 0x1p65L
45 #elif LDBL_MANT_DIG == 113
46 #define FROM_UNDERFLOW 0x1p114L
47 #else
48 #error Unsupported long double format
49 #endif
50
51 long double
logbl(long double x)52 logbl(long double x)
53 {
54 union ieee_ext_u u;
55
56 if (x == 0.0L)
57 return -1.0L / fabsl(x); /* -HUGE_VALL + exception */
58
59 u.extu_ld = x;
60
61 if (u.extu_ext.ext_exp == EXT_EXP_INFNAN)
62 return fabsl(x); /* NaN or +Inf */
63
64 if (u.extu_ext.ext_exp == 0) {
65 /*
66 * Scale denormalized numbers slightly,
67 * so that they are normal.
68 */
69 u.extu_ld *= FROM_UNDERFLOW;
70 return u.extu_ext.ext_exp - EXT_EXP_BIAS - LDBL_MANT_DIG - 1;
71 }
72 return u.extu_ext.ext_exp - EXT_EXP_BIAS;
73
74 }
75
76 #endif
77