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

Author: Gerd Isenberg

Date: 10:15:09 11/19/02

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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

Hi Gian-Carlo,

I think that's evident. If the none bitboarders have to use implicite native
data-width of 64 bit integers, they have to transfer 32 additional zero bits
without any additional information for each integer access. Of course you will
pack some data, but all the local ints...

So the information density for bitboarders grows with 64bit-architectures
relative to none bitboarders. That also effects register usage, and that's IMHO
more important. On x86-32bit architectures you can only hold three bitboards in
registers, and thats even most a hard task. Actually, if you have a local
routine with three bitboards and a few ints on the stack, there are a lot
register/memory moves. Simply the data-width doubles the number of bitboard
registers, not considered the increase in general purpose registers, or with
hammer the number of mmx- and 128-bit xmm registers.

Whether a bitboard based program is stronger than a none bitboard program
depends obviuosly also on other things, but in principle :)

Cheers,
Gerd



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