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Subject: Re: Differences between 0x88 ,10x12 and Bitboards!?

Author: Vincent Diepeveen

Date: 11:24:04 11/19/02

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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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