lkasami.c

在linux系统下开发研究移动通信的工具型代码

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

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

#include "lkasami.h"
#include "gf.h"
#include "lmseq.h"
#include "mseq.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.  To generate the other sequence in the
 * family, ie the sub-m-sequence itself, use find_longsubpoly() to get the
 * primitive polynomial of the sub-m-sequence and use mseq_create() to actually
 * generate the m-sequence.
 */
LKasami *lkasami_create( unsigned deg, char *poly, unsigned long seed )
{
  LKasami *kasami;
  unsigned long subpoly;
  unsigned subdeg;

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

  if ( deg > 62 ) {
    fprintf(stderr, "lkasami_create: ..cannot handle deg > 62\n");
    return NULL;  /* too high degree */
  }
  
  subdeg  = deg >> 1;
  subpoly = find_longsubpoly( deg, poly );
  kasami = (LKasami*) malloc( sizeof(LKasami) );
  kasami->mseq0 = lmseq_create( deg, poly, 0, 1 );
  kasami->mseq1 = mseq_create ( subdeg, subpoly, seed & ((1<<subdeg)-1) );

  return kasami;
}

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

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