vde-2/src/vde_cryptcab/crc32.c

   1 /*
   2  * VDE Cryptcab
   3  * Copyright © 2006-2008 Daniele Lacamera
   4  * from an idea by Renzo Davoli
   5  *
   6  * Released under the terms of GNU GPL v.2
   7  * (http://www.gnu.org/licenses/old-licenses/gpl-2.0.html)
   8  * with the additional exemption that
   9  * compiling, linking, and/or using OpenSSL is allowed.
  10  *
  11  * based on implementation by Finn Yannick Jacobs  Krzysztof Dabrowski, ElysiuM deeZine
  12  *
  13  */
  14
  15 #include <stdio.h>
  16 #include <stdlib.h>
  17 #include <sys/types.h>
  18
  19 #include <config.h>
  20 #include <vde.h>
  21 #include <vdecommon.h>
  22
  23 /* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
  24  *              so make sure, you call it before using the other
  25  *              functions!
  26  */
  27 u_int32_t crc_tab[256];
  28
  29 /* chksum_crc() -- to a given block, this one calculates the
  30  *                              crc32-checksum until the length is
  31  *                              reached. the crc32-checksum will be
  32  *                              the result.
  33  */
  34 u_int32_t chksum_crc32 (unsigned char *block, unsigned int length)
  35 {
  36    register unsigned long crc;
  37    unsigned long i;
  38
  39    crc = 0xFFFFFFFF;
  40    for (i = 0; i < length; i++)
  41    {
  42       crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
  43    }
  44    return (crc ^ 0xFFFFFFFF);
  45 }
  46
  47
  48 unsigned char *crc32(unsigned char *block, unsigned int len)
  49 {
  50         register unsigned long crc=chksum_crc32(block,len);
  51         unsigned char *res=malloc(4);
  52
  53         res[0]=crc&0x000000FF;
  54         res[1]=(crc&0x0000FF00)>>8;
  55         res[2]=(crc&0x00FF0000)>>16;
  56         res[3]=(crc&0xFF000000)>>24;
  57         return res;
  58 }
  59
  60
  61 /* chksum_crc32gentab() --      to a global crc_tab[256], this one will
  62  *                              calculate the crcTable for crc32-checksums.
  63  *                              it is generated to the polynom [..]
  64  */
  65
  66 void chksum_crc32gentab ()
  67 {
  68    unsigned long crc, poly;
  69    int i, j;
  70
  71    poly = 0xEDB88320L;
  72    for (i = 0; i < 256; i++)
  73    {
  74       crc = i;
  75       for (j = 8; j > 0; j--)
  76       {
  77          if (crc & 1)
  78          {
  79             crc = (crc >> 1) ^ poly;
  80          }
  81          else
  82          {
  83             crc >>= 1;
  84          }
  85       }
  86       crc_tab[i] = crc;
  87    }
  88 }