lib/xz/xz_crc32.c

   1 /*
   2  * CRC32 using the polynomial from IEEE-802.3
   3  *
   4  * Authors: Lasse Collin <lasse.collin@tukaani.org>
   5  *          Igor Pavlov <http://7-zip.org/>
   6  *
   7  * This file has been put into the public domain.
   8  * You can do whatever you want with this file.
   9  */
  10
  11 /*
  12  * This is not the fastest implementation, but it is pretty compact.
  13  * The fastest versions of xz_crc32() on modern CPUs without hardware
  14  * accelerated CRC instruction are 3-5 times as fast as this version,
  15  * but they are bigger and use more memory for the lookup table.
  16  */
  17
  18 #include "xz_private.h"
  19
  20 /*
  21  * STATIC_RW_DATA is used in the pre-boot environment on some architectures.
  22  * See <linux/decompress/mm.h> for details.
  23  */
  24 #ifndef STATIC_RW_DATA
  25 #       define STATIC_RW_DATA static
  26 #endif
  27
  28 STATIC_RW_DATA uint32_t xz_crc32_table[256];
  29
  30 XZ_EXTERN void xz_crc32_init(void)
  31 {
  32         const uint32_t poly = 0xEDB88320;
  33
  34         uint32_t i;
  35         uint32_t j;
  36         uint32_t r;
  37
  38         for (i = 0; i < 256; ++i) {
  39                 r = i;
  40                 for (j = 0; j < 8; ++j)
  41                         r = (r >> 1) ^ (poly & ~((r & 1) - 1));
  42
  43                 xz_crc32_table[i] = r;
  44         }
  45
  46         return;
  47 }
  48
  49 XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc)
  50 {
  51         crc = ~crc;
  52
  53         while (size != 0) {
  54                 crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
  55                 --size;
  56         }
  57
  58         return ~crc;
  59 }