libm/cos.c

   1 /*
   2  *  ZeX/OS
   3  *  Copyright (C) 2008  Tomas 'ZeXx86' Jedrzejek (zexx86@zexos.org)
   4  *  Copyright (C) 2009  Tomas 'ZeXx86' Jedrzejek (zexx86@zexos.org)
   5  *
   6  *  This program is free software: you can redistribute it and/or modify
   7  *  it under the terms of the GNU General Public License as published by
   8  *  the Free Software Foundation, either version 3 of the License, or
   9  *  (at your option) any later version.
  10  *
  11  *  This program is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU General Public License
  17  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  *
  19  *  Thanks for Oroborus
  20  */
  21
  22
  23 #include <math.h>
  24 #include <stdlib.h>
  25
  26 static double fact (double x)
  27 {
  28         if (x == 0.0)
  29                 return 1.0;
  30
  31         return x * fact (x - 1.0);
  32 }
  33
  34 static double expo (double x, int a)
  35 {
  36         double ret;
  37         int i;
  38
  39         ret = 1.0;
  40
  41         for (i = 0 ; i < abs (a); i ++)
  42                 ret *= x;
  43
  44         return (a > 0 ? ret : 1 / ret);
  45 }
  46
  47 double cos (double x)
  48 {
  49         double ret;
  50         int i;
  51
  52         ret = 0.0;
  53
  54         while (x < 0)
  55                 x += 2 * M_PI;
  56
  57         while (x > 2 * M_PI)
  58                 x -= 2 * M_PI;
  59
  60         for (i = 0 ; i < 16; i ++)
  61                 ret += (expo (-1, i) * expo (x, 2 * i)) / fact (2 * i);
  62
  63         return ret;
  64 }
  65