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Linux/lib/crc64.c

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  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 
 34 MODULE_DESCRIPTION("CRC64 calculations");
 35 MODULE_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  */
 44 u64 __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 }
 57 EXPORT_SYMBOL_GPL(crc64_be);
 58 

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