lib/crc.c

   1 /* crc.c - crc function  */
   2 /*
   3  *  GRUB  --  GRand Unified Bootloader
   4  *  Copyright (C) 2008  Free Software Foundation, Inc.
   5  *
   6  *  GRUB is free software: you can redistribute it and/or modify
   7  *  it under the terms of the GNU General Public License as published by
   8  *  the Free Software Foundation, either version 3 of the License, or
   9  *  (at your option) any later version.
  10  *
  11  *  GRUB is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU General Public License
  17  *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <grub/types.h>
  21 #include <grub/lib/crc.h>
  22
  23 static grub_uint32_t crc32_table [256];
  24
  25 static void
  26 init_crc32_table (void)
  27 {
  28   auto grub_uint32_t reflect (grub_uint32_t ref, int len);
  29   grub_uint32_t reflect (grub_uint32_t ref, int len)
  30     {
  31       grub_uint32_t result = 0;
  32       int i;
  33
  34       for (i = 1; i <= len; i++)
  35         {
  36           if (ref & 1)
  37             result |= 1 << (len - i);
  38           ref >>= 1;
  39         }
  40
  41       return result;
  42     }
  43
  44   grub_uint32_t polynomial = 0x04c11db7;
  45   int i, j;
  46
  47   for(i = 0; i < 256; i++)
  48     {
  49       crc32_table[i] = reflect(i, 8) << 24;
  50       for (j = 0; j < 8; j++)
  51         crc32_table[i] = (crc32_table[i] << 1) ^
  52             (crc32_table[i] & (1 << 31) ? polynomial : 0);
  53       crc32_table[i] = reflect(crc32_table[i], 32);
  54     }
  55 }
  56
  57 grub_uint32_t
  58 grub_getcrc32 (grub_uint32_t crc, void *buf, int size)
  59 {
  60   int i;
  61   grub_uint8_t *data = buf;
  62
  63   if (! crc32_table[1])
  64     init_crc32_table ();
  65
  66   crc^= 0xffffffff;
  67
  68   for (i = 0; i < size; i++)
  69     {
  70       crc = (crc >> 8) ^ crc32_table[(crc & 0xFF) ^ *data];
  71       data++;
  72     }
  73
  74   return crc ^ 0xffffffff;
  75 }