#include <iostream.h>
#include <math.h>
#include <stdlib.h>

void hsi2rgb(double* rgb, double* hsi);

int main(int argc, char** argv) {
   if (argc != 4) {
      cout << "Usage: " << argv[0] << " R G B" << endl;
      exit(1);
   }

   double H = atof(argv[1]);
   double S = atof(argv[2]);
   double I = atof(argv[3]);

   double hsi[3];
   hsi[0] = H;
   hsi[1] = S;
   hsi[2] = I;

   double rgb[3];

   hsi2rgb(rgb, hsi);

   cout << "R = " << (int)(256 * rgb[0] + 0.5) << endl;
   cout << "G = " << (int)(256 * rgb[1] + 0.5) << endl;
   cout << "B = " << (int)(256 * rgb[2] + 0.5) << endl;

   return 0;
}



//////////////////////////////
//
// hsi2rgb -- convert from HSI color space to RGB color space.
//

#ifndef PI
   #define PI M_PI
#endif

void hsi2rgb(double* rgb, double* hsi) {
   double& R = rgb[0];
   double& G = rgb[1];
   double& B = rgb[2];
   double& H = hsi[0];
   double& S = hsi[1];
   double& I = hsi[2];

   double r;
   double g;
   double b;

   if (H < 1.0/3.0) {
      b = (1-S)/3;
      r = (1+S*cos(2*PI*H)/cos(PI/3-2*PI*H))/3.0;
      g = 1 - (b + r);
   } else if (H < 2.0/3.0) {
      H = H - 1.0/3.0;
      r = (1-S)/3;
      g = (1+S*cos(2*PI*H)/cos(PI/3-2*PI*H))/3.0;
      b = 1 - (r+g);
   } else {
      H = H - 2.0/3.0;
      g = (1-S)/3;
      b = (1+S*cos(2*PI*H)/cos(PI/3-2*PI*H))/3.0;
      r = 1 - (g+b);
   }

   R = I * r * 3;
   G = I * g * 3;
   B = I * b * 3;
}