src/add-ons/kernel/file_systems/btrfs/crc_table.cpp

   1 //----------------------------------------------------------------------
   2 //  This software is part of the OpenBeOS distribution and is covered
   3 //  by the MIT License.
   4 //
   5 //  Copyright (c) 2003 Tyler Dauwalder, tyler@dauwalder.net
   6 //---------------------------------------------------------------------
   7
   8 /*! \file crc_table.cpp
   9
  10         Standalone program to generate the CRC table used for calculating
  11         UDF tag id CRC values.
  12
  13         This code based off of crc code in UDF-2.50 specs, as permitted.
  14         See UDF-2.50 6.5 for more information.
  15
  16         Reflected version by Jéme Duval
  17 */
  18
  19
  20 #include "system_dependencies.h"
  21
  22
  23 typedef unsigned int uint32 ;
  24
  25 uint32
  26 reflect32 (uint32 b)
  27 {
  28         uint32 rw = 0;
  29
  30         for (int i = 0; i < 32; i++){
  31                 if (b & 1)
  32                         rw |= 1 << (31 - i);
  33                 b >>= 1;
  34         }
  35         return rw;
  36 }
  37
  38
  39 int
  40 main(int argc, char* argv[]) {
  41         uint32 crc, poly;
  42
  43         if (argc != 2) {
  44                 fprintf(stderr, "USAGE: crc_table <octal polynomial=3667067501 for btrfs>\n");
  45                 return 0;
  46         }
  47
  48         sscanf(argv[1], "%lo", &poly);
  49
  50         printf("//! CRC 0%o table, as generated by crc_table.cpp\n", poly);
  51         printf("static uint32 crc_table[256] = { \n");
  52         for (int n = 0; n < 256; n++) {
  53                 if (n % 8 == 0)
  54                         printf("    ");
  55                 crc = reflect32(n);
  56                 for (int i = 0; i < 8; i++) {
  57                         if (crc & 0x80000000)
  58                                 crc = (crc << 1) ^ poly;
  59                         else
  60                                 crc <<= 1;
  61                 }
  62                 crc = reflect32(crc);
  63                 printf("0x%08x%s ", crc, (n != 255 ? "," : ""));
  64                 if (n % 8 == 7)
  65                         printf("\n");
  66         }
  67         printf("};\n");
  68         return 0;
  69 }