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 g...@2ndquadrant.com Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
