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Subject: Re: [PATCH 2/4] lib: add crc64 calculation routines
To:     Randy Dunlap <rdunlap@infradead.org>, linux-kernel@vger.kernel.org
Cc:     linux-bcache@vger.kernel.org, linux-block@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Michael Lyle <mlyle@lyle.org>,
        Kent Overstreet <kent.overstreet@gmail.com>,
        "Luis R . Rodriguez" <mcgrof@suse.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kate Stewart <kstewart@linuxfoundation.org>
References: <20180716165507.23100-1-colyli@suse.de>
 <20180716165507.23100-3-colyli@suse.de>
 <d8b85ecd-8641-bdaf-5238-6cd2523a5701@infradead.org>
From:   Coly Li <colyli@suse.de>
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Message-ID: <b9a92e52-2e60-5a20-7a75-6e190c0635d3@suse.de>
Date:   Tue, 17 Jul 2018 11:19:07 +0800
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On 2018/7/17 1:57 AM, Randy Dunlap wrote:
> 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@suse.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 Randy,

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

In v2 series it will be 0x0ULL :-)

Thanks.

Coly Li