1*0a6a1f1dSLionel Sambuc /* $NetBSD: n_log2.c,v 1.1 2014/03/06 10:57:01 martin Exp $ */
2*0a6a1f1dSLionel Sambuc /*-
3*0a6a1f1dSLionel Sambuc * Copyright (c) 2014 The NetBSD Foundation, Inc.
4*0a6a1f1dSLionel Sambuc * All rights reserved.
5*0a6a1f1dSLionel Sambuc *
6*0a6a1f1dSLionel Sambuc * This code is derived from software contributed to The NetBSD Foundation
7*0a6a1f1dSLionel Sambuc * by Martin Husemann <martin@NetBSD.org>.
8*0a6a1f1dSLionel Sambuc *
9*0a6a1f1dSLionel Sambuc * Redistribution and use in source and binary forms, with or without
10*0a6a1f1dSLionel Sambuc * modification, are permitted provided that the following conditions
11*0a6a1f1dSLionel Sambuc * are met:
12*0a6a1f1dSLionel Sambuc * 1. Redistributions of source code must retain the above copyright
13*0a6a1f1dSLionel Sambuc * notice, this list of conditions and the following disclaimer.
14*0a6a1f1dSLionel Sambuc * 2. Redistributions in binary form must reproduce the above copyright
15*0a6a1f1dSLionel Sambuc * notice, this list of conditions and the following disclaimer in the
16*0a6a1f1dSLionel Sambuc * documentation and/or other materials provided with the distribution.
17*0a6a1f1dSLionel Sambuc *
18*0a6a1f1dSLionel Sambuc * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
19*0a6a1f1dSLionel Sambuc * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
20*0a6a1f1dSLionel Sambuc * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
21*0a6a1f1dSLionel Sambuc * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
22*0a6a1f1dSLionel Sambuc * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
23*0a6a1f1dSLionel Sambuc * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
24*0a6a1f1dSLionel Sambuc * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
25*0a6a1f1dSLionel Sambuc * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
26*0a6a1f1dSLionel Sambuc * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
27*0a6a1f1dSLionel Sambuc * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
28*0a6a1f1dSLionel Sambuc * POSSIBILITY OF SUCH DAMAGE.
29*0a6a1f1dSLionel Sambuc */
30*0a6a1f1dSLionel Sambuc
31*0a6a1f1dSLionel Sambuc /* LOG2(X)
32*0a6a1f1dSLionel Sambuc * RETURN THE BASE 10 LOGARITHM OF x
33*0a6a1f1dSLionel Sambuc *
34*0a6a1f1dSLionel Sambuc * Required kernel function:
35*0a6a1f1dSLionel Sambuc * log(x)
36*0a6a1f1dSLionel Sambuc *
37*0a6a1f1dSLionel Sambuc * Method :
38*0a6a1f1dSLionel Sambuc * log(x)
39*0a6a1f1dSLionel Sambuc * log2(x) = ---------
40*0a6a1f1dSLionel Sambuc * log(2)
41*0a6a1f1dSLionel Sambuc */
42*0a6a1f1dSLionel Sambuc
43*0a6a1f1dSLionel Sambuc #define _LIBM_STATIC
44*0a6a1f1dSLionel Sambuc #include "mathimpl.h"
45*0a6a1f1dSLionel Sambuc
46*0a6a1f1dSLionel Sambuc
47*0a6a1f1dSLionel Sambuc static const double ln2 = .6931471805599453094172321214581765680755;
48*0a6a1f1dSLionel Sambuc
49*0a6a1f1dSLionel Sambuc double
log2(double x)50*0a6a1f1dSLionel Sambuc log2(double x)
51*0a6a1f1dSLionel Sambuc {
52*0a6a1f1dSLionel Sambuc return log(x)/ln2;
53*0a6a1f1dSLionel Sambuc }
54*0a6a1f1dSLionel Sambuc
55*0a6a1f1dSLionel Sambuc float
log2f(float x)56*0a6a1f1dSLionel Sambuc log2f(float x)
57*0a6a1f1dSLionel Sambuc {
58*0a6a1f1dSLionel Sambuc return logf(x)/ln2;
59*0a6a1f1dSLionel Sambuc }
60