crc.c

mpeg 解复用

/*
 * cyclic redundancy check 16 and 32 bit
 * Copyright (C) 1999 Christian Wolff
 * for Convergence Integrated Media GmbH (http://www.convergence.de)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <sys/types.h>
#include "crc.h"

#ifdef CRC16MSBF
u_int16_t crc_16_table[256];
#endif
#ifdef CRC32MSBF
u_int32_t crc_32_table[256];
#endif

// generate the tables of CRC-16 and CRC-32 remainders for all possible bytes
void gen_crc_table() { 
  register int i,j;  
#ifdef CRC16MSBF
  register u_int16_t crc16;
#endif
#ifdef CRC32MSBF
  register u_int32_t crc32;
#endif
  for (i=0; i<256; i++) {
#ifdef CRC16MSBF
    crc16=(u_int16_t)i << 8;
#endif
#ifdef CRC32MSBF
    crc32=(u_int32_t)i << 24;
#endif
    for (j=0; j<8; j++) {
#ifdef CRC16MSBF
      crc16 = (crc16 << 1) ^ ((crc16 & (1<<15)) ? POLYNOMIAL_16_MSBF : 0);
#endif
#ifdef CRC32MSBF
      crc32 = (crc32 << 1) ^ ((crc32 & (1<<31)) ? POLYNOMIAL_32_MSBF : 0);
#endif
    }
#ifdef CRC16MSBF
    crc_16_table[i]=crc16; 
#endif
#ifdef CRC32MSBF
    crc_32_table[i]=crc32; 
#endif
  }
}

// update the CRC on the data block one byte at a time
#ifdef CRC16MSBF
u_int16_t update_crc_16_block(u_int16_t crc, char *data_block_ptr, int data_block_size)
{
  register int i;
  for (i=data_block_size; i>0; i--)
    crc=update_crc_16(crc, *data_block_ptr++);
  return crc;
}
#endif

#ifdef CRC32MSBF
u_int32_t update_crc_32_block(u_int32_t crc, char *data_block_ptr, int data_block_size)
{
  register int i;
  for (i=data_block_size; i>0; i--)
    crc=update_crc_32(crc, *data_block_ptr++);
  return crc;
}
#endif

#ifdef CRC16MSBF
void crc16_calc (char *data,
    int size,
    char *crc)
{
  u_int16_t c;
  c = CRC_INIT_16;
  while (--size >= 0) {
    c = update_crc_16 (c,*data++);
  }
  crc[1] = c; c >>= 8;
  crc[0] = c;
}
#endif

#ifdef CRC32MSBF
void crc32_calc (char *data,
    int size,
    char *crc)
{
  u_int32_t c;
  c = CRC_INIT_32;
  while (--size >= 0) {
    c = update_crc_32 (c,*data++);
  }
  crc[3] = c; c >>= 8;
  crc[2] = c; c >>= 8;
  crc[1] = c; c >>= 8;
  crc[0] = c;
}
#endif