/*
 * 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.
 *
 * Hacked by CyberLeo to make it capable of digesting long streams
 *  one buffer at a time. - 20090105
 */

/* based on implementation by Finn Yannick Jacobs */

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

/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
 *                so make sure, you call it before using the other
 *                functions!
 */
uint32_t chksum_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, uint32_t *chksum_crc)
{
   register unsigned long crc;
   unsigned long i;
   
   crc = *chksum_crc ^ 0xFFFFFFFF;
   for (i = 0; i < length; i++)
   {
      crc = ((crc >> 8) & 0x00FFFFFF) ^ chksum_crc_tab[(crc ^ *block++) & 0xFF];
   }
   *chksum_crc = crc ^ 0xFFFFFFFF;
   return *chksum_crc;
}

/* chksum_crc32_gentab() --      to a global crc_tab[256], this one will
 *                                calculate the crcTable for crc32-checksums.
 *                                it is generated to the polynom [..]
 */

void chksum_crc32_gentab ()
{
   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;
         }
      }
      chksum_crc_tab[i] = crc;
   }
}