mrog.c

Orthogonal Codes

/*
 * $Log: mrog.c,v $
 * Revision 1.1  2000/05/03 14:30:04  bjc97r
 * Initial revision
 *
 */
char *_mrog_id = "$Id: mrog.c,v 1.1 2000/05/03 14:30:04 bjc97r Exp $";

#include <stdio.h>
#include <stdlib.h>
#include "mrog.h"

// It create an Multi-Rate Orthogonal Gold(MROG) code generator with
// the given connection polynomials and for the given index'th code.
// The MROG generator is returned.
Mrog *mrog_create( unsigned deg, unsigned long poly0, unsigned long poly1,
		   unsigned index )
{
  Mrog *mrog;
  int   bindex; /* base ogold index */

  if ( deg > 31 ) {
    fprintf(stderr, "mrog_create: ..cannot handle deg > 31\n");
    return NULL; /* too big degree of polynomial */
  }

  mrog = (Mrog*) malloc( sizeof(Mrog) );

  bindex = index & ( (1<<deg) - 1 ); /* last deg bits of the index */
  mrog->id = ogold_create( deg, poly0, poly1, bindex );
  mrog->period   = 1 << deg; /* 2^deg */
  mrog->og_cnt   = 1;        /* 1..period */
  mrog->ext_code = index >> deg; /* upper part of the index */
  mrog->ext_cnt  = 0;        /* 0.. */
  mrog->ext      = 0;        /* 0 or 1 */

  return mrog;
}

void mrog_free( Mrog *mrog )
{
  ogold_free( mrog->id );
  free( (void*) mrog );
}

// mrog() gives the next multi-rate orthogonal Gold code sequence.
char mrog( Mrog *id )
{
  char seq;
  
  seq = id->ext ^ ogold( id->id );

  if ( id->og_cnt == id->period ) {
    /* ogold code cycles at this point. update extension modifier */
    unsigned long dump;
    char          tmp;

    id->og_cnt = 1;
    id->ext_cnt++;

    /* Sylvester construction or Hadamard transform of the original
       orthogonal Gold code sequence */
    dump = id->ext_cnt & id->ext_code;
    tmp = 0;
    for( tmp = 0; dump; dump >>= 1 ) {
      tmp ^= dump & 1;
    }
    id->ext = tmp;
  }
  else {
    id->og_cnt++;
  }

  return seq;
}