kasami.c

kasami伪码产生器

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

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

#include "kasami.h"
#include "gf.h"

//
// It creates a Kasami code generator. Only the generator polynomial 
// for the main m-sequence is specified through the arguments. 
// The sub-sequence polynomial is calculated internally based on the
// main polynomial. The relative shift of the subsequence is controlled
// by the subsequence 'seed' argument. The initial state of the main
// m-sequence generator is fixed to 1. Note that 'seed' does not correspond
// to a 'serial shift' directly, if this makes sense to you. The valid range
// of 'seed' is from 0 to 2^(deg/2)-1, so that 2^(deg/2) number of different
// Kasami sequences can be obtained.
//
Kasami *kasami_create( unsigned deg, ulong poly, ulong seed )
{
  Kasami *kasami;
  ulong subpoly;
  unsigned subdeg;

  if ( deg & 1 ) {
    fprintf(stderr, "kasami_create: .. the degree of the main m-seq polynomial"
	    " should be even.\n");
    return NULL; // odd main degree
  }

  if ( deg > 30 ) {
    fprintf(stderr, "kasami_create: ..cannot handle deg > 30\n");
    fprintf(stderr, "try kasamil_create() for the degrees upto 62.\n");
    return NULL; // too high degree
  }
  
  subdeg  = deg >> 1;
  subpoly = find_subpoly( deg, poly );

  kasami = (Kasami*) malloc( sizeof(Kasami) );
  kasami->mseq0 = mseq_create( deg, poly, 1 );
  kasami->mseq1 = mseq_create( subdeg, subpoly, seed & ((1<<subdeg)-1) );

  return kasami;
}

//
// kasami_free() deallocates the memory space for 
// the Kasami sequence generator.
//
void kasami_free( Kasami *kasami )
{
  mseq_free( kasami->mseq0 );
  mseq_free( kasami->mseq1 );
  free( kasami );
}

// kasami() gives the next Kasami sequence in unipolar form, ie 1 or 0.
char kasami( Kasami *id )
{
  return mseq(id->mseq0) ^ mseq(id->mseq1);
}