src/add-ons/kernel/file_systems/ext2/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         Reversed version by Jérôme Duval
  17 */
  18
  19 #include <stdio.h>
  20 #include <sys/types.h>
  21
  22 int
  23 main(int argc, char *argv[]) {
  24         ulong crc, poly;
  25
  26         if (argc != 2) {
  27                 fprintf(stderr, "USAGE: crc_table <octal polynomial=120001 for ext2>\n");
  28                 return 0;
  29         }
  30
  31         sscanf(argv[1], "%lo", &poly);
  32         if (poly & 0xffff0000) {
  33                 fprintf(stderr, "ERROR: polynomial is too large, sucka.\n");
  34                 return 0;
  35         }
  36
  37         printf("//! CRC 0%o table, as generated by crc_table.cpp\n", poly);
  38         printf("static uint16 crc_table[256] = { \n");
  39         for (int n = 0; n < 256; n++) {
  40                 if (n%8 == 0)
  41                         printf("    ");
  42                 crc = n;
  43                 for (int i = 0; i < 8; i++) {
  44                         if (crc & 0x0001)
  45                                 crc = (crc >> 1) ^ poly;
  46                         else
  47                                 crc >>= 1;
  48                 }
  49                 printf("0x%04x%s ", crc, (n != 255 ? "," : ""));
  50                 if (n%8 == 7)
  51                         printf("\n");
  52         }
  53         printf("};\n");
  54         return 0;
  55 }