/*The trig-functions sine, cosine, tan, atan*/

#include <conio.h>
#include <unistd.h>
#include <dbutton.h>
#include <dkey.h>

#define CORDIC_gain 1.646760258

double Phase (int k) /*in degrees*/
{
   switch(k)
     {
        case 1:  return  45.0000000;
        case 2:  return  26.5650512;
        case 3:  return  14.0362435;
        case 4:  return  7.12501635;
        case 5:  return  3.57633437;
        case 6:  return  1.78991061;
        case 7:  return  0.89517371;
        case 8:  return  0.44761417;
        case 9:  return  0.22381050;
        case 10: return 0.11190568;
        case 11: return 0.05595289;
        case 12: return 0.02797645;
        case 13: return 0.01398823;
        case 14: return 0.00699411;
        case 15: return 0.00349706;
        case 16: return 0.00174853;
        case 17: return 0.00087426;
        case 18: return 0.00043713;
        case 19: return 0.00021857;
        case 20: return 0.00010928;
        case 21: return 0.00005464;
        case 22: return 0.00002732;
        case 23: return 0.00001366;
        case 24: return 0.00000683;
        case 25: return 0.00000341;
        case 26: return 0.00000177;
        case 27: return 0.00000085;
        case 28: return 0.00000042;
        case 29: return 0.00000021;
        case 30: return 0.00000010;
        case 31: return 0.00000005;
        case 32: return 0.00000002;
        case 33: return 0.00000001;
     default: return 888;
     }
}

double trig(double alpha,int idx)
{  double a=1;
    double b=0;
    double kL=1;
    double Theta=0;
    double Temp,beta,tan;
     int L,sign,c;

  beta=alpha;
  c=0;
  while(beta>180) beta-=360; /*beta must be smaller than 180° */
  while(beta<-180) beta+=360; /*beta must be greater than -180° */
  if(beta>90 ) { beta=180-beta; c=1;} /*quadrant II */
  if(beta<-90) { beta=-beta-180; c=1;} /*quadrant III */
   

   for(L=1;L<34;L++)
      {
         if(Theta<beta) { sign=1; }  else { sign=-1; }
         Theta+=sign*Phase(L);
         Temp=a; 
         a-=b*kL*sign; 
         b+=Temp*kL*sign;
         kL/=2;
      }
    a/=CORDIC_gain;  /*a=cos(alpha)*/
    b/=CORDIC_gain; /*b=sin(alpha)*/
    if(c==1) a=-a;
    if(a!=0) {tan=b/a;} else { if(b>0) {tan=999999;} else {tan=-999999;} }
    switch(idx)
          {
             case 1: return a;  /*give the cosine */
             case 2: return b; /* give the sine */
             case 3: return tan;  /*give the tan */
           default: return 888;
           }
}

double atan(double x)
{  double a,b,Temp;
    double kL=1;
    double Theta=90;
    int L,sign;

  if(x>0) {b=1;} else {b=-1;}
  Theta*=-b; /*starting value +90 or -90 depending sign of x*/
  a=x*b; /*a will always be positive */

  Temp=a; /*now rotate by +/- 90°; this could be done more quickly, but for better understanding*/
  a=b*b;
  b=-Temp*b; 
   

   for(L=1;L<34;L++)
      {
         if(b>0) { sign=-1; }  else { sign=1; }
         Theta+=sign*Phase(L);
         Temp=a; 
         a-=b*kL*sign; 
         b+=Temp*kL*sign;
         kL/=2;
      }
  if(x>0) { return Theta+90;} else {return Theta-90;}
}

int main()
{
   int j;  /*This is only test program*/
   int p;
   for (j=-10;j<11;j++)
     {
       cputs("x");
       sleep(1);
       lcd_int(j);
       sleep(1);

       cputs("atan");
       sleep(1);
       p=atan(j);
       lcd_int(p);
                             

        while(RELEASED(dbutton(),BUTTON_VIEW)); /*wait until view-button pressed*/
    }
   return 0;
}