Re: Enabling Checksums

On 3/15/13 5:32 AM, Ants Aasma wrote:
> Best case using the CRC32 instruction would be 6.8 bytes/cycle [1].
> But this got me thinking about how to do this faster...
> [1] http://www.drdobbs.com/parallel/fast-parallelized-crc-computation-using/229401411

The optimization work you went through here looked very nice. 
Unfortunately, a few things seem pushing toward using a CRC16 instead of 
the Fletcher approach.  It seems possible to execute a CRC16 in a 
reasonable enough time, in the same neighborhood as the Fletcher one. 
And there is some hope that hardware acceleration for CRCs will be 
available in a system API/compiler feature one day, making them even 
cheaper.

Ants, do you think you could take a similar look at optimizing a CRC16 
calculation?  I'm back to where I can do a full performance comparison 
run again starting tomorrow, with the latest version of this patch, and 
I'd like to do that with a CRC16 implementation or two.  I'm not sure if 
it's possible to get a quicker implementation because the target is a 
CRC16, or whether it's useful to consider truncating a CRC32 into a CRC16.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
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