RE: [boost] crc_fast: inefficiency

From: Reid Sweatman (reid_of_diamonds_at_[hidden])
Date: 2001-03-21 06:54:59

Probably right on that, but you can also get pretty fast byte reversals with
a lookup table...unless that's how the code is already doing it; haven't
looked.

Reid Sweatman

> -----Original Message-----
> From: Vladimir Prus [mailto:ghost_at_[hidden]]
> Sent: Tuesday, March 06, 2001 7:17 AM
> To: boost_at_[hidden]
> Subject: [boost] crc_fast: inefficiency
>
>
>
> crc_fast, despite its name, has a significant performance
> problem. Namely, if
> input is reversed, the code call a routine to reverse each byte. That
> bit-tossing routine is slow, and as far as I can tell, all practical
> implementation avoid reversing byte, but instread reverse everything else.
>
> I compared performance of current crc_fast with implementation that uses
> optimization mentioned above. On 1Meg buffer with random data crc_fast is
> 10 times slower. Without bytes reversing, it's only 2 times slower. So,
> changing code seems worthwhile.
>
> --
> Regards,
> Vladimir
>
>
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