lib/xz/xz_crc32.c

   1 // SPDX-License-Identifier: 0BSD
   2
   3 /*
   4  * CRC32 using the polynomial from IEEE-802.3
   5  *
   6  * Authors: Lasse Collin <lasse.collin@tukaani.org>
   7  *          Igor Pavlov <https://7-zip.org/>
   8  */
   9
  10 /*
  11  * This is not the fastest implementation, but it is pretty compact.
  12  * The fastest versions of xz_crc32() on modern CPUs without hardware
  13  * accelerated CRC instruction are 3-5 times as fast as this version,
  14  * but they are bigger and use more memory for the lookup table.
  15  */
  16
  17 #include "xz_private.h"
  18
  19 /*
  20  * STATIC_RW_DATA is used in the pre-boot environment on some architectures.
  21  * See <linux/decompress/mm.h> for details.
  22  */
  23 #ifndef STATIC_RW_DATA
  24 #       define STATIC_RW_DATA static
  25 #endif
  26
  27 STATIC_RW_DATA uint32_t xz_crc32_table[256];
  28
  29 void xz_crc32_init(void)
  30 {
  31         const uint32_t poly = 0xEDB88320;
  32
  33         uint32_t i;
  34         uint32_t j;
  35         uint32_t r;
  36
  37         for (i = 0; i < 256; ++i) {
  38                 r = i;
  39                 for (j = 0; j < 8; ++j)
  40                         r = (r >> 1) ^ (poly & ~((r & 1) - 1));
  41
  42                 xz_crc32_table[i] = r;
  43         }
  44
  45         return;
  46 }
  47
  48 uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc)
  49 {
  50         crc = ~crc;
  51
  52         while (size != 0) {
  53                 crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
  54                 --size;
  55         }
  56
  57         return ~crc;
  58 }