poly.cpp

1、简介 此代码是IS0 13818-5 MPEG2系统层协议分析代码

/* Copyright (C) 1995, Tektronix Inc. All Rights Reserved.
 *
 *   Usage Restrictions
 *
 * License is granted to copy, to use, and to make and to use derivative
 * works for research and evaluation purposes only.
 *
 *   Disclaimer of Warranty
 *
 * These software programs are available to the user without any license
 * fee or royalty on an "as is" basis.  Tektronix Inc. disclaims any and
 * all warranties, whether express, implied, or statuary, including any
 * implied warranties or merchantability or of fitness for a particular
 * purpose.  In no event shall the copyright-holder be liable for any 
 * incidental, punitive, or consequential damages of any kind whatsoever
 * arising from the use of these programs.
 *
 * This disclaimer of warranty extends to the user of these programs and
 * user's customers, employees, agents, transferees, successors, and
 * assigns.
 *
 * The Tektronix Inc. does not represent or warrant that the programs
 * furnished hereunder are free of infringement of any third-party
 * patents.
*/

/* Poly implementation */

#include "Poly.H"

extern "C"
{
#include <stdio.h>
}

static unsigned short int g[] =
{0,1,1,0,1,1,0,1,
 1,0,1,1,1,0,0,0,
 1,0,0,0,0,0,1,1,
 0,0,1,0,0,0,0,0};

Poly::Poly ()
{
  for (int i=0; i<32; i++)
    shift_reg[i] = 1;
}

void Poly::push_bit (char data_bit) // data_bit range = '0', '1'
{
  int i;
  char obit;
  
  obit = data_bit -= '0';
  
  data_bit ^= shift_reg[31];
  i = 31;
  while (i !=0)
    {
      if (g[i])
	shift_reg[i] = shift_reg[i-1] ^ data_bit;
      else
	shift_reg[i] = shift_reg[i-1];
      i--;
    }
  shift_reg[0] = data_bit;
}

int Poly::poly_cmp (char* bstr) 
{
    char bit;
    int    i;
    unsigned long vali, valg;

    // bit 31 is MSB
    vali = valg = 0;
    for (i=31; i >= 0; i--)
      {
	vali <<=  1;
	valg <<=  1;
	vali += bstr[i] - '0'; 
	valg += shift_reg[i]; 
      }
    if ( vali == valg) return 1;
    else if ( vali == ~valg ) return 2;
    else return 0;
}

void Poly::print_bits ()
{
  for (int i = 31; i >= 0; --i)
    putc('0'+shift_reg[i], stdout);
}