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
36static 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
83vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC)
84
85ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E)
86
87#ifdef vccast
88#define	ln10hi	vccast(ln10hi)
89#endif
90
91__weak_alias(log10l, _log10l)
92__strong_alias(_log10l, _log10)
93
94__weak_alias(log10, _log10)
95double
96log10(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
105__weak_alias(log10f, _log10f)
106float
107log10f(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