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SubjectRe: [PATCH v4 1/3] lib: add crc64 calculation routines
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On 2018/7/24 12:26 PM, Eric Biggers wrote:
> On Thu, Jul 19, 2018 at 12:55:43AM +0800, Coly Li wrote:
>> This patch adds the re-write crc64 calculation routines for Linux kernel.
>> The CRC64 polynomical arithmetic follows ECMA-182 specification, inspired
>
> "polynomical" => "polynomial". Same everywhere else in the patches.
>

Hi Eric,

Thanks for your careful review. I will post a fixing patch to fix all
these issues.

Coly Li

>> + * crc64table[256] is the lookup table of a table-driver 64-bit CRC
>
> "table-driver" => "table-driven"
>
>> + * calculation, which is generated by gen_crc64table.c in kernel build
>> + * time. The polynomial of crc64 arithmetic is from ECMA-182 specification
>> + * as well, which is defined as,
>> + *
>> + * x^64 + x^62 + x^57 + x^55 + x^54 + x^53 + x^52 + x^47 + x^46 + x^45 +
>> + * x^40 + x^39 + x^38 + x^37 + x^35 + x^33 + x^32 + x^31 + x^29 + x^27 +
>> + * x^24 + x^23 + x^22 + x^21 + x^19 + x^17 + x^13 + x^12 + x^10 + x^9 +
>> + * x^7 + x^4 + x + 1
>> + *
>> + * Copyright 2018 SUSE Linux.
>> + * Author: Coly Li <colyli@suse.de>
>> + */
>> +
>> +#include <linux/module.h>
>> +#include <linux/types.h>
>> +#include "crc64table.h"
>> +
>> +MODULE_DESCRIPTION("CRC64 calculations");
>> +MODULE_LICENSE("GPL v2");
>> +
>> +/**
>> + * crc64_be - Calculate bitwise big-endian ECMA-182 CRC64
>> + * @crc: seed value for computation. 0 for a new CRC computing, or the
>> + * previous crc64 value if computing incrementally.
>
> "0 or (u64)~0 for a new CRC calculation". Both conventions are common in CRCs.
> In fact the all-ones convention is generally considered better, because it
> causes leading zeroes in the data to affect the checksum.
>
>> + * @p: pointer to buffer over which CRC64 is run
>> + * @len: length of buffer @p
>> + */
>> +u64 __pure crc64_be(u64 crc, const void *p, size_t len)
>> +{
>> + size_t i, t;
>> +
>> + const unsigned char *_p = p;
>> +
>> + for (i = 0; i < len; i++) {
>> + t = ((crc >> 56) ^ (*_p++)) & 0xFF;
>> + crc = crc64table[t] ^ (crc << 8);
>> + }
>> +
>> + return crc;
>> +}
>> +EXPORT_SYMBOL_GPL(crc64_be);
>> diff --git a/lib/gen_crc64table.c b/lib/gen_crc64table.c
>> new file mode 100644
>> index 000000000000..8296b0c3ea30
>> --- /dev/null
>> +++ b/lib/gen_crc64table.c
>> @@ -0,0 +1,68 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Generate lookup table for the talbe-driven CRC64 calculation.
>
> "talbe-driven" => "table-driven"
>
>> + *
>> + * gen_crc64table is executed in kernel build time and generates
>> + * lib/crc64table.h. This header is included by lib/crc64.c for
>> + * the table-driver CRC64 calculation.
>
> "table-driver" => "table-driven"
>
>> + *
>> + * See lib/crc64.c for more information about which specification
>> + * and polynomical arithmetic that gen_crc64table.c follows to
>> + * generate the lookup table.
>> + *
>> + * Copyright 2018 SUSE Linux.
>> + * Author: Coly Li <colyli@suse.de>
>> + */
>> +#include <inttypes.h>
>> +#include <stdio.h>
>> +
>> +#include <linux/swab.h>
>> +
>> +#define CRC64_ECMA182_POLY 0x42F0E1EBA9EA3693ULL
>> +
>> +static int64_t crc64_table[256] = {0};
>
> This really should be uint64_t, not int64_t.
>
>> +
>> +static void generate_crc64_table(void)
>> +{
>> + uint64_t i, j, c, crc;
>> +
>> + for (i = 0; i < 256; i++) {
>> + crc = 0;
>> + c = i << 56;
>> +
>> + for (j = 0; j < 8; j++) {
>> + if ((crc ^ c) & 0x8000000000000000ULL)
>> + crc = (crc << 1) ^ CRC64_ECMA182_POLY;
>> + else
>> + crc <<= 1;
>> + c <<= 1;
>> + }
>> +
>> + crc64_table[i] = crc;
>> + }
>> +}
>> +
>> +static void print_crc64_table(void)
>> +{
>> + int i;
>> +
>> + printf("/* this file is generated - do not edit */\n\n");
>> + printf("#include <linux/types.h>\n");
>> + printf("#include <linux/cache.h>\n\n");
>> + printf("static const u64 ____cacheline_aligned crc64table[256] = {\n");
>> + for (i = 0; i < 256; i++) {
>> + printf("\t0x%016" PRIx64 "ULL", crc64_table[i]);
>> + if (i & 0x1)
>> + printf(",\n");
>> + else
>> + printf(", ");
>> + }
>> + printf("};\n");
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + generate_crc64_table();
>> + print_crc64_table();
>> + return 0;
>> +}
>> --
>> 2.17.1
>>
>
> - Eric
>

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