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crc32.cc
/*
 * efone - Distributed internet phone system.
 *
 * (c) 1999,2000 Krzysztof Dabrowski
 * (c) 1999,2000 ElysiuM deeZine
 *
 * 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.
 *
 */

/* based on implementation by Finn Yannick Jacobs */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include "crc32.h"

/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
 *          so make sure, you call it before using the other
 *          functions!
 */
uint32_t crc_tab[256];

/* chksum_crc() -- to a given block, this one calculates the
 *                      crc32-checksum until the length is
 *                      reached. the crc32-checksum will be
 *                      the result.
 */
uint32_t chksum_crc32 (unsigned char *block, unsigned int length)
{
   register unsigned long crc;
   unsigned long i;

   crc = 0xFFFFFFFF;
   for (i = 0; i < length; i++)
   {
      crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
   }
   return (crc ^ 0xFFFFFFFF);
}

/* chksum_crc32gentab() --      to a global crc_tab[256], this one will
 *                      calculate the crcTable for crc32-checksums.
 *                      it is generated to the polynom [..]
 */

void chksum_crc32gentab ()
{
   unsigned long crc, poly;
   int i, j;

   poly = 0xEDB88320L;
   for (i = 0; i < 256; i++)
   {
      crc = i;
      for (j = 8; j > 0; j--)
      {
       if (crc & 1)
       {
          crc = (crc >> 1) ^ poly;
       }
       else
       {
          crc >>= 1;
       }
      }
      crc_tab[i] = crc;
   }
}

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