Author: Christophe Theron
Date: 10:30:57 11/19/02
Go up one level in this thread
On November 19, 2002 at 13:15:09, Gerd Isenberg 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
>
>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
You have just explained why the bitboarders are less handicapped on 64 bits
machines.
You have not explained why they are supposed to have "a bit of performance
advantage on 64 bits processors".
Christophe
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