LXR linux/lib/crc64.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Normal 64-bit CRC calculation.
   4 *
   5 * This is a basic crc64 implementation following ECMA-182 specification,
   6 * which can be found from,
   7 * https://www.ecma-international.org/publications/standards/Ecma-182.htm
   8 *
   9 * Dr. Ross N. Williams has a great document to introduce the idea of CRC
  10 * algorithm, here the CRC64 code is also inspired by the table-driven
  11 * algorithm and detail example from this paper. This paper can be found
  12 * from,
  13 * http://www.ross.net/crc/download/crc_v3.txt
  14 *
  15 * crc64table[256] is the lookup table of a table-driven 64-bit CRC
  16 * calculation, which is generated by gen_crc64table.c in kernel build
  17 * time. The polynomial of crc64 arithmetic is from ECMA-182 specification
  18 * as well, which is defined as,
  19 *
  20 * x^64 + x^62 + x^57 + x^55 + x^54 + x^53 + x^52 + x^47 + x^46 + x^45 +
  21 * x^40 + x^39 + x^38 + x^37 + x^35 + x^33 + x^32 + x^31 + x^29 + x^27 +
  22 * x^24 + x^23 + x^22 + x^21 + x^19 + x^17 + x^13 + x^12 + x^10 + x^9 +
  23 * x^7 + x^4 + x + 1
  24 *
  25 * Copyright 2018 SUSE Linux.
  26 *   Author: Coly Li <colyli@suse.de>
  27 */
  28
  29#include <linux/module.h>
  30#include <linux/types.h>
  31#include <linux/crc64.h>
  32#include "crc64table.h"
  33
  34MODULE_DESCRIPTION("CRC64 calculations");
  35MODULE_LICENSE("GPL v2");
  36
  37/**
  38 * crc64_be - Calculate bitwise big-endian ECMA-182 CRC64
  39 * @crc: seed value for computation. 0 or (u64)~0 for a new CRC calculation,
  40 *       or the previous crc64 value if computing incrementally.
  41 * @p: pointer to buffer over which CRC64 is run
  42 * @len: length of buffer @p
  43 */
  44u64 __pure crc64_be(u64 crc, const void *p, size_t len)
  45{
  46        size_t i, t;
  47
  48        const unsigned char *_p = p;
  49
  50        for (i = 0; i < len; i++) {
  51                t = ((crc >> 56) ^ (*_p++)) & 0xFF;
  52                crc = crc64table[t] ^ (crc << 8);
  53        }
  54
  55        return crc;
  56}
  57EXPORT_SYMBOL_GPL(crc64_be);
  58