1/*      $NetBSD: n_log10.c,v 1.5 2002/06/15 00:10:17 matt 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#ifndef lint
32#if 0
33static char sccsid[] = "@(#)log10.c	8.1 (Berkeley) 6/4/93";
34#endif
35#endif /* not lint */
36
37/* LOG10(X)
38 * RETURN THE BASE 10 LOGARITHM OF x
39 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
40 * CODED IN C BY K.C. NG, 1/20/85;
41 * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85.
42 *
43 * Required kernel function:
44 *	log(x)
45 *
46 * Method :
47 *			     log(x)
48 *		log10(x) = ---------  or  [1/log(10)]*log(x)
49 *			    log(10)
50 *
51 *    Note:
52 *	  [log(10)]   rounded to 56 bits has error  .0895  ulps,
53 *	  [1/log(10)] rounded to 53 bits has error  .198   ulps;
54 *	  therefore, for better accuracy, in VAX D format, we divide
55 *	  log(x) by log(10), but in IEEE Double format, we multiply
56 *	  log(x) by [1/log(10)].
57 *
58 * Special cases:
59 *	log10(x) is NaN with signal if x < 0;
60 *	log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
61 *	log10(NaN) is that NaN with no signal.
62 *
63 * Accuracy:
64 *	log10(X) returns the exact log10(x) nearly rounded. In a test run
65 *	with 1,536,000 random arguments on a VAX, the maximum observed
66 *	error was 1.74 ulps (units in the last place).
67 *
68 * Constants:
69 * The hexadecimal values are the intended ones for the following constants.
70 * The decimal values may be used, provided that the compiler will convert
71 * from decimal to binary accurately enough to produce the hexadecimal values
72 * shown.
73 */
74
75#define _LIBM_STATIC
76#include "mathimpl.h"
77
78vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC)
79
80ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E)
81
82#ifdef vccast
83#define	ln10hi	vccast(ln10hi)
84#endif
85
86
87double
88log10(double x)
89{
90#if defined(__vax__)||defined(tahoe)
91	return(log(x)/ln10hi);
92#else	/* defined(__vax__)||defined(tahoe) */
93	return(ivln10*log(x));
94#endif	/* defined(__vax__)||defined(tahoe) */
95}
96