lib/libm/noieee_src/n_log2.c

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