libm/cos.c

   1 /*
   2  *  ZeX/OS
   3  *  Copyright (C) 2008  Tomas 'ZeXx86' Jedrzejek (zexx86@gmail.com)
   4  *
   5  *  This program is free software: you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation, either version 3 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19
  20 #include <math.h>
  21
  22
  23 double cos (double x)
  24 {
  25         int neg = 0;
  26         int cnt = 0;
  27
  28         x = fmod (x, PI_X2);
  29
  30         if (fabs (x) > PI && fabs (x) < PI_X2)
  31                 neg = 1;
  32
  33         x = fmod (x, PI);
  34
  35         double eps = 0.000001;
  36         double exp = x * x;
  37         double numerator = 1.0;
  38         double denominator = 1.0;
  39         double tmp = 0.0;
  40         double cos = 1;
  41         int sign = 1;
  42         int i = 2;
  43
  44         do {
  45                 numerator *= exp;
  46                 denominator *= i * (i-1);
  47                 sign *= -1;
  48                 tmp = numerator / denominator * sign;
  49                 cos += tmp;
  50                 i += 2;
  51                 cnt ++;
  52         } while (fabs (tmp) >= eps);
  53
  54         if (neg == 1)
  55                 cos *= -1;
  56
  57         return cos;
  58 }
  59