linux-kernel - Re: [PATCH 2/4] lib: add crc64 calculation routines

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Message-ID: <d8b85ecd-8641-bdaf-5238-6cd2523a5701@infradead.org>
Date:   Mon, 16 Jul 2018 10:57:41 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Coly Li <colyli@...e.de>, linux-kernel@...r.kernel.org
Cc:     linux-bcache@...r.kernel.org, linux-block@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Michael Lyle <mlyle@...e.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        "Luis R . Rodriguez" <mcgrof@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>
Subject: Re: [PATCH 2/4] lib: add crc64 calculation routines

On 07/16/2018 09:55 AM, Coly Li wrote:
> 
> diff --git a/lib/crc64.c b/lib/crc64.c
> new file mode 100644
> index 000000000000..03f078303bd3
> --- /dev/null
> +++ b/lib/crc64.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Normal 64bit CRC calculation.
> + *
> + * This is a basic crc64 implementation following ECMA-182 specification,
> + * which can be found from,
> + * http://www.ecma-international.org/publications/standards/Ecma-182.htm
> + *
> + * Dr. Ross N. Williams has a great document to introduce the idea of CRC
> + * algorithm, here the CRC64 code is also inspired by the table-driven
> + * algorithm and detail example from this paper. This paper can be found
> + * from,
> + * http://www.ross.net/crc/download/crc_v3.txt
> + *
> + * crc64table_le[256] is the lookup table of a table-driver 64bit CRC
> + * 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@...e.de>
> + *
> + */
> +
> +#include <linux/module.h>
> +#include <uapi/linux/types.h>
> +#include "crc64table.h"
> +
> +MODULE_DESCRIPTION("CRC64 calculations");
> +MODULE_LICENSE("GPL");
> +
> +__le64 crc64_le_update(__le64 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) ^ (__le64)(*p++)) & 0xFF;
> +		crc = crc64table_le[t] ^ (crc << 8);
> +	}
> +
> +	return crc;
> +}
> +EXPORT_SYMBOL_GPL(crc64_le_update);
> +
> +__le64 crc64_le(const void *p, size_t len)
> +{
> +	__le64 crc = 0x0000000000000000ULL;

Hi,
What's wrong with just using 0ULL ?

thanks.

> +
> +	crc = crc64_le_update(crc, p, len);
> +
> +	return crc;
> +}


-- 
~Randy