walsh.c

在linux系统下开发研究移动通信的工具型代码

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

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

#include "walsh.h"

/*
 * It create a Walsh code generator of the given index with the
 * given seed. The Walsh code generator is returned.
 */
Walsh *walsh_create( unsigned long index, unsigned long seed )
{
  Walsh *walsh;

  walsh = (Walsh*) malloc( sizeof(Walsh) );
  walsh->state = seed;
  walsh->index = index;

  return walsh;
}

void walsh_free( Walsh *walsh )
{
  free(walsh);
}

/*
 * walsh() gives the next Walsh sequence of the Walsh code generator.
 * The used algorithm is the direct implementation of one given
 * at pp542 of "Introduction to Spread Spectrum Communicatrions" by
 * Peterson et al.
 */
char walsh( Walsh *id )
{
  unsigned long dump; /* dumped current state */
  char seq; /* the Wlash sequence */
  
  dump = id->index & id->state;
  id->state++;

  seq = 0;
  while( dump ) {
    seq ^= dump & 1;
    dump >>= 1;
  }

  return seq;
}