lmseq.c

在linux系统下开发研究移动通信的工具型代码

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

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

#include "lmseq.h"
#include "u2long.h"

/*
 * lmseq_create() differs from mseq_create() in that it can handle
 * higher order generator polynomials up to 63.
 * The polynomial should be given by the octal representation of it,
 * for example, lmseq = lmseq_create( 40, "020000012000005", 0, 1 ).
 * seed1 corresponds to upper 32bits and seed0 lower 32bits 
 * as the initial state of the PN registers.
 */
LMseq * lmseq_create( unsigned deg, char * poly,
		      unsigned long seed1, unsigned long seed0  )
{
  LMseq * lmseq;
  u2long poly0;

  if ( deg > 63 ) {
    fprintf(stderr, "lmseq_create: ..cannot handle deg > 63\n");
    return NULL;
  }

  lmseq = (LMseq *) malloc( sizeof(LMseq) );

  lmseq->state0 = seed0;
  lmseq->state1 = seed1;

  poly0 = strtou2long( poly );
  u2long_rshift( &poly0, 1 );
  lmseq->mask0 = poly0.l;
  lmseq->mask1 = poly0.h;

  return lmseq;
}

/* lmseq_free() deallocates the memory space for the m-sequence generator. */
void lmseq_free( LMseq * id )
{
  free( (void*) id );
}

/*
 * lmseq() gives the next m-sequence bit of the m-sequence generator.
 * The generated bit is unipolar, ie 1 or 0.
 */
char lmseq( LMseq * id )
{
  char seq, tmp;
  
  seq = id->state0 & 1;
  tmp = id->state1 & 1;
  id->state0 >>= 1;
  if ( tmp ) id->state0 |= 0x80000000;
  id->state1 >>= 1;
  if ( seq ) {
    id->state0 ^= id->mask0;
    id->state1 ^= id->mask1;
  }

  return seq;
}