1 /* $NetBSD: n_log10.c,v 1.8 2024/07/16 14:52:50 riastradh Exp $ */
2 /*
3 * Copyright (c) 1985, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the University nor the names of its contributors
15 * may be used to endorse or promote products derived from this software
16 * without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 */
30
31 #include <sys/cdefs.h>
32 __RCSID("$NetBSD: n_log10.c,v 1.8 2024/07/16 14:52:50 riastradh Exp $");
33
34 #ifndef lint
35 #if 0
36 static char sccsid[] = "@(#)log10.c 8.1 (Berkeley) 6/4/93";
37 #endif
38 #endif /* not lint */
39
40 /* LOG10(X)
41 * RETURN THE BASE 10 LOGARITHM OF x
42 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
43 * CODED IN C BY K.C. NG, 1/20/85;
44 * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85.
45 *
46 * Required kernel function:
47 * log(x)
48 *
49 * Method :
50 * log(x)
51 * log10(x) = --------- or [1/log(10)]*log(x)
52 * log(10)
53 *
54 * Note:
55 * [log(10)] rounded to 56 bits has error .0895 ulps,
56 * [1/log(10)] rounded to 53 bits has error .198 ulps;
57 * therefore, for better accuracy, in VAX D format, we divide
58 * log(x) by log(10), but in IEEE Double format, we multiply
59 * log(x) by [1/log(10)].
60 *
61 * Special cases:
62 * log10(x) is NaN with signal if x < 0;
63 * log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
64 * log10(NaN) is that NaN with no signal.
65 *
66 * Accuracy:
67 * log10(X) returns the exact log10(x) nearly rounded. In a test run
68 * with 1,536,000 random arguments on a VAX, the maximum observed
69 * error was 1.74 ulps (units in the last place).
70 *
71 * Constants:
72 * The hexadecimal values are the intended ones for the following constants.
73 * The decimal values may be used, provided that the compiler will convert
74 * from decimal to binary accurately enough to produce the hexadecimal values
75 * shown.
76 */
77
78 #include "namespace.h"
79
80 #define _LIBM_STATIC
81 #include "mathimpl.h"
82
83 vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC)
84
85 ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E)
86
87 #ifdef vccast
88 #define ln10hi vccast(ln10hi)
89 #endif
90
__weak_alias(log10l,_log10l)91 __weak_alias(log10l, _log10l)
92 __strong_alias(_log10l, _log10)
93
94 __weak_alias(log10, _log10)
95 double
96 log10(double x)
97 {
98 #if defined(__vax__)||defined(tahoe)
99 return(log(x)/ln10hi);
100 #else /* defined(__vax__)||defined(tahoe) */
101 return(ivln10*log(x));
102 #endif /* defined(__vax__)||defined(tahoe) */
103 }
104
__weak_alias(log10f,_log10f)105 __weak_alias(log10f, _log10f)
106 float
107 log10f(float x)
108 {
109 #if defined(__vax__)||defined(tahoe)
110 return(logf(x)/ln10hi);
111 #else /* defined(__vax__)||defined(tahoe) */
112 return(ivln10*log(x));
113 #endif /* defined(__vax__)||defined(tahoe) */
114 }
115