LXR linux/lib/xz/xz

   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
  28STATIC_RW_DATA uint32_t xz_crc32_table[256];
  29
  30XZ_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
  49XZ_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}
  60