tools/torrent/mktorrent_crc/crc32.c

   1 /* Copyright (C) 2012 Connor Olding
   2  *
   3  * This program is licensed under the terms of the MIT License, and
   4  * is distributed without any warranty.  You should have received a
   5  * copy of the license along with this program; see the file LICENSE.
   6  */
   7
   8 typedef unsigned long ulong;
   9 #include "crc32.h"
  10
  11 ulong crc_reflect(ulong input)
  12 {
  13         ulong reflected = 0;
  14         int i;
  15         for (i = 0; i < 4 * 8; i++) {
  16                 reflected <<= 1;
  17                 reflected |= input & 1;
  18                 input >>= 1;
  19         }
  20         return reflected;
  21 }
  22
  23 void crc_fill_table(ulong *table, int big, ulong polynomial)
  24 {
  25         ulong lsb = (big) ? 1 << 31 : 1; /* least significant bit */
  26         ulong poly = (big) ? polynomial : crc_reflect(polynomial);
  27         int c, i;
  28
  29         for (c = 0; c < CRC_TABLE_SIZE; c++, table++) {
  30                 *table = (big) ? c << 24 : c;
  31                 for (i = 0; i < 8; i++) {
  32                         if (*table & lsb) {
  33                                 *table = (big) ? *table << 1 : *table >> 1;
  34                                 *table ^= poly;
  35                         } else {
  36                                 *table = (big) ? *table << 1 : *table >> 1;
  37                         }
  38                         *table &= 0xFFFFFFFF;
  39                 }
  40         }
  41 }
  42
  43 void crc_be_cycle(ulong *table, ulong *remainder, char c)
  44 {
  45         ulong byte = table[(((*remainder) >> 24) ^ c) & 0xff];
  46         *remainder = (((*remainder) << 8) ^ byte) & 0xFFFFFFFF;
  47 }
  48
  49 void crc_le_cycle(ulong *table, ulong *remainder, char c)
  50 {
  51         ulong byte = table[((*remainder) ^ c) & 0xFF];
  52         *remainder = ((*remainder) >> 8) ^ byte;
  53 }