vde-2/vde_cryptcab/crc32.c

   1 /*
   2  * efone - Distributed internet phone system.
   3  *
   4  * (c) 1999,2000 Krzysztof Dabrowski
   5  * (c) 1999,2000 ElysiuM deeZine
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License
   9  * as published by the Free Software Foundation; either version
  10  * 2 of the License, or (at your option) any later version.
  11  *
  12  */
  13
  14 /* based on implementation by Finn Yannick Jacobs */
  15
  16 #include <stdio.h>
  17 #include <stdlib.h>
  18 #include <sys/types.h>
  19
  20 /* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
  21  *              so make sure, you call it before using the other
  22  *              functions!
  23  */
  24 u_int32_t crc_tab[256];
  25
  26 /* chksum_crc() -- to a given block, this one calculates the
  27  *                              crc32-checksum until the length is
  28  *                              reached. the crc32-checksum will be
  29  *                              the result.
  30  */
  31 u_int32_t chksum_crc32 (unsigned char *block, unsigned int length)
  32 {
  33    register unsigned long crc;
  34    unsigned long i;
  35
  36    crc = 0xFFFFFFFF;
  37    for (i = 0; i < length; i++)
  38    {
  39       crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
  40    }
  41    return (crc ^ 0xFFFFFFFF);
  42 }
  43
  44
  45 unsigned char *crc32(unsigned char *block, unsigned int len)
  46 {
  47         register unsigned long crc=chksum_crc32(block,len);
  48         unsigned char *res=malloc(4);
  49
  50         res[0]=crc&0x000000FF;
  51         res[1]=(crc&0x0000FF00)>>8;
  52         res[2]=(crc&0x00FF0000)>>16;
  53         res[3]=(crc&0xFF000000)>>24;
  54         return res;
  55 }
  56
  57
  58 /* chksum_crc32gentab() --      to a global crc_tab[256], this one will
  59  *                              calculate the crcTable for crc32-checksums.
  60  *                              it is generated to the polynom [..]
  61  */
  62
  63 void chksum_crc32gentab ()
  64 {
  65    unsigned long crc, poly;
  66    int i, j;
  67
  68    poly = 0xEDB88320L;
  69    for (i = 0; i < 256; i++)
  70    {
  71       crc = i;
  72       for (j = 8; j > 0; j--)
  73       {
  74          if (crc & 1)
  75          {
  76             crc = (crc >> 1) ^ poly;
  77          }
  78          else
  79          {
  80             crc >>= 1;
  81          }
  82       }
  83       crc_tab[i] = crc;
  84    }
  85 }