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  * http://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 "crc64table.h"
  32
  33 MODULE_DESCRIPTION("CRC64 calculations");
  34 MODULE_LICENSE("GPL v2");
  35
  36 /**
  37  * crc64_be - Calculate bitwise big-endian ECMA-182 CRC64
  38  * @crc: seed value for computation. 0 or (u64)~0 for a new CRC calculation,
  39         or the previous crc64 value if computing incrementally.
  40  * @p: pointer to buffer over which CRC64 is run
  41  * @len: length of buffer @p
  42  */
  43 u64 __pure crc64_be(u64 crc, const void *p, size_t len)
  44 {
  45         size_t i, t;
  46
  47         const unsigned char *_p = p;
  48
  49         for (i = 0; i < len; i++) {
  50                 t = ((crc >> 56) ^ (*_p++)) & 0xFF;
  51                 crc = crc64table[t] ^ (crc << 8);
  52         }
  53
  54         return crc;
  55 }
  56 EXPORT_SYMBOL_GPL(crc64_be);