嵌入式系统中sin和cos的快速算法

  #define   R1   -0.1666665668e+0   
  #define   R2     0.8333025139e-2   
  #define   R3   -0.1980741872e-3   
  #define   R4     0.2601903036e-5   
    
  /****************************************************************************/   
  /*     COS()   -   Cosine                                                   */   
  /*     Based   on   the   algorithm   from   "Software   Manual   for   the   Elementary    
  /*     Functions",   Cody   and   Waite,   Prentice   Hall   1980,   chapter   8.    
  /*     N   =   round(x   /   PI   +   1/2)   -   0.5                        */   
  /*     f   =   x   -   N   *   PI                                           */   
  /*     g   =   f   *   f                                                    */   
  /*     R   =   polynomial   expression                                      */   
  /*     result   =   f   +   f   *   R                                       */   
  /*     if   N   is   even,   result   =   -   result                        */   
  /*     This   will   return   the   wrong   result   for   x   >=   MAXINT   *   PI    
  /****************************************************************************/   
  double   cos(double   x)   
  {   
          int   sign;                       /*   the   sign   of   the   result   */   
          double   xn,   f,   g,   rg,   result;   
          int   n;   
    
          /**************************************************************************/   
          /*   cos(x)   =   cos(-x)      
          /**************************************************************************/   
          x   =   fabs(x);   
    
          /**************************************************************************/   
          /*   n   =   round(x/PI   +   1/2)   (can   be   rounded   this   way,   since   positive   number)   */