LXR busybox/libbb/crc32.c

   1/* vi: set sw=4 ts=4: */
   2/*
   3 * CRC32 table fill function
   4 * Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
   5 * (I can't really claim much credit however, as the algorithm is
   6 * very well-known)
   7 *
   8 * The following function creates a CRC32 table depending on whether
   9 * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
  10 * required. Admittedly, there are other CRC32 polynomials floating
  11 * around, but Busybox doesn't use them.
  12 *
  13 * endian = 1: big-endian
  14 * endian = 0: little-endian
  15 *
  16 * Licensed under GPLv2, see file LICENSE in this source tree.
  17 */
  18
  19#include "libbb.h"
  20
  21uint32_t *global_crc32_table;
  22
  23uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian)
  24{
  25        uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
  26        uint32_t c;
  27        int i, j;
  28
  29        if (!crc_table)
  30                crc_table = xmalloc(256 * sizeof(uint32_t));
  31
  32        for (i = 0; i < 256; i++) {
  33                c = endian ? (i << 24) : i;
  34                for (j = 8; j; j--) {
  35                        if (endian)
  36                                c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
  37                        else
  38                                c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
  39                }
  40                *crc_table++ = c;
  41        }
  42
  43        return crc_table - 256;
  44}
  45
  46uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
  47{
  48        const void *end = (uint8_t*)buf + len;
  49
  50        while (buf != end) {
  51                val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf];
  52                buf = (uint8_t*)buf + 1;
  53        }
  54        return val;
  55}
  56
  57uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
  58{
  59        const void *end = (uint8_t*)buf + len;
  60
  61        while (buf != end) {
  62                val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8);
  63                buf = (uint8_t*)buf + 1;
  64        }
  65        return val;
  66}
  67