Vlnk/src/crc32.c

   1 /******************************************************************************
   2  * crc32.c  ----
   3  *
   4  * Copyright (c) 2022, longpanda <admin@ventoy.net>
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 3 of the
   9  * License, or (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  18  *
  19  */
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22 #include <stdint.h>
  23 #include <string.h>
  24 #include "vlnk.h"
  25
  26 static uint32_t crc32c_table [256];
  27
  28 /* Helper for init_crc32c_table.  */
  29 static uint32_t reflect (uint32_t ref, int len)
  30 {
  31   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 static void init_crc32c_table (void)
  45 {
  46   uint32_t polynomial = 0x1edc6f41;
  47   int i, j;
  48
  49   for(i = 0; i < 256; i++)
  50     {
  51       crc32c_table[i] = reflect(i, 8) << 24;
  52       for (j = 0; j < 8; j++)
  53         crc32c_table[i] = (crc32c_table[i] << 1) ^
  54             (crc32c_table[i] & (1 << 31) ? polynomial : 0);
  55       crc32c_table[i] = reflect(crc32c_table[i], 32);
  56     }
  57 }
  58
  59 uint32_t ventoy_getcrc32c (uint32_t crc, const void *buf, int size)
  60 {
  61   int i;
  62   const uint8_t *data = buf;
  63
  64   if (! crc32c_table[1])
  65     init_crc32c_table ();
  66
  67   crc^= 0xffffffff;
  68
  69   for (i = 0; i < size; i++)
  70     {
  71       crc = (crc >> 8) ^ crc32c_table[(crc & 0xFF) ^ *data];
  72       data++;
  73     }
  74
  75   return crc ^ 0xffffffff;
  76 }
  77