Re: [PATCH 6/6] Automatically switch to crc32 checksum for index when it's too large
On Feb 6, 2012, at 12:54 AM, Nguyen Thai Ngoc Duy <pclouds@gmail.com> wrote:
> 2012/2/6 Dave Zarzycki <zarzycki@apple.com>:
>> Which crc32 polynomial is being used? crc32c (a.k.a. Castagnoli)? It would be great if this were the same polynomial that Intel implements in hardware via SSE4.2.
>
> It's zlib's crc32.
That's too bad. Zlib uses crc32, not crc32c. The Intel instruction is crc32c and is 2-3 times faster than the best software based implementation.
http://www.strchr.com/crc32_popcnt
Show 14 quoted lines
>
>> On Feb 5, 2012, at 9:48 PM, Nguyễn Thái Ngọc Duy <pclouds@gmail.com> wrote:
>>
>>> An experiment with -O3 is done on Intel D510@1.66GHz. At around 250k
>>> entries, index reading time exceeds 0.5s. Switching to crc32 brings it
>>> back lower than 0.2s.
>>>
>>> On 4M files index, reading time with SHA-1 takes ~8.4, crc32 2.8s.
> --
> Duy
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Dave Zarzycki <zarzycki@apple.com>