Author: Vincent Diepeveen
Date: 11:24:04 11/19/02
Go up one level in this thread
On November 19, 2002 at 14:11:18, Robert Hyatt wrote: >On November 19, 2002 at 12:25:11, Gian-Carlo Pascutto wrote: > >>On November 19, 2002 at 11:35:24, Robert Hyatt wrote: >> >>>Bitboards have a bit of a performance advantage on 64 bit processors, >> >>Proof? >> >>-- >>GCP > >Counter-proof? > >Seems intuitively obvious to me. Bitmaps seem to suffer _no_ performance >penalty on >X86 with 32 bits, compared to 0x88. Seems intuitively obvious to me that they >will pick >up speed on a machine that does 64 bit operations. > >Bruce and I did this comparison when he used the alpha in the WMCCC (1997 I >think). > >He re-compiled ferret for the alpha, did the same for Crafty. My speed >improvement was >significantly better than his on the _same_ machine. Because of the 64 bit >stuff. His program >didn't need any 64 bit stuff so it was wasted... > >Best "proof" is to try it. I have... But at that time i also proofed that you generated moves already 2.2 times slower than i did. If you then get 33% faster because of getting 64 bits, that doesn't proof anything. If we look at the speed at specint of crafty versus specint of K7, then we see that a 1Ghz alpha 21264c, which is their fastest CPU, is performing at the OFFICIAL benchmark like a 1.33Ghz K7. So if we roughly give you 33% for bitboards going from 32 to 64 bits, then that's simply the maximum you can claim for it. The argument that specint is not allowing inline assembly is not valid. I do not use inline assembly in my program either (with exception of locking at the x86). So let's keep it a fair compare. So first a slowdown of a factor 2 (used to be 2.2) then winning back 33% because of getting 64 bits, that isn't very impressive to me. It sure is intuitively VERY CLEAR to me that just having 1 bit of info spreaded over loads of bitboards is not a very good plan, because for any complex chess pattern you simply need more instructions than non-bitboarders do.
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