// ------------------------------------------------------------------------
// File: primint.c
// Date: April 5, 2002
// Description: Generate a PRIMITIVE interleaver. Output is the interleaver
// array in a files with name specified at command line
//
// The permuted position is computed as a recursion:
//
//          position[i] = ( position[i-1] + root ) modulo N
//
// Care must be taken in selecting N and root to obtain a valid interlaver
// ------------------------------------------------------------------------
// This program is complementary material for the book:
//
// R.H. Morelos-Zaragoza, The Art of Error Correcting Coding, Wiley, 2002.
//
// ISBN 0471 49581 6
//
// This and other programs are available at http://the-art-of-ecc.com
//
// You may use this program for academic and personal purposes only. 
// If this program is used to perform simulations whose results are 
// published in a journal or book, please refer to the book above.
//
// The use of this program in a commercial product requires explicit
// written permission from the author. The author is not responsible or 
// liable for damage or loss that may be caused by the use of this program. 
//
// Copyright (c) 2002. Robert H. Morelos-Zaragoza. All rights reserved.
// ------------------------------------------------------------------------

#include <stdio.h>
#include <math.h>
#include <float.h>
#include <limits.h>
#define NMAX 16384

main(int argc, char *argv[])
{

int interleaver[NMAX];
int deinterleaver[NMAX];
int check[NMAX];
int i, j, position;
int N;                                 // Interleaver length
int root;                              // Primitive root modulo N
char name1[40];
FILE *fp1;

  // Command line processing
  if (argc != 4)
    {
      printf("Usage %s N  primitive_root  INT_file\n", argv[0]);
      exit(0);
    }

  sscanf(argv[1],"%d", &N);
  sscanf(argv[2],"%d", &root);
  sscanf(argv[3],"%s", name1);

  fp1 = fopen(name1,"w");

  interleaver[0] = 0;
  deinterleaver[0] = 0;
  position = 0;

  for (i=1; i<N; i++)
    {
      position = (position + root) % N;
      interleaver[i] = position;
    }    

  // Check if a valid interleaver is obtained ...
  for (i=0; i<N; i++) check[i] = 0;
  for (i=0; i<N; i++) check[interleaver[i]] = 1;
  for (i=0; i<N; i++) 
    if (!check[i]) {
        printf("This is not a valid interleaver!\n");
        exit(0);
      }

  for (i=0; i<N; i++)
    {
      fprintf(fp1, "%d\n", interleaver[i]);
      printf("%5d -> %5d\n",i,interleaver[i]);
    }

  fclose(fp1);

}