libm/sin.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 sin (double x)
  24 {
  25         int neg = 0;
  26
  27         x = fmod (x, PI_X2);
  28
  29         if (fabs (x) > PI && fabs (x) < PI_X2)
  30                 neg = 1;
  31
  32         x = fmod (x, PI);
  33
  34         double eps = 1;
  35         double exp = x * x;
  36         double numerator = x;
  37         double denominator = 1.0;
  38         double tmp = 0.0;
  39         double sin = x;
  40         int sign = 1;
  41         int i = 1;
  42
  43         do {
  44                 numerator *= exp;
  45                 denominator *= (i*2+1) * (i*2);
  46                 sign *= -1;
  47                 tmp = numerator / denominator * sign;
  48                 sin += tmp;
  49                 i ++;
  50         } while (fabs (tmp) >= eps);
  51
  52         if (neg == 1)
  53                 sin *= -1;
  54
  55         return sin;
  56 }