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

Author: Robert Hyatt

Date: 11:27:26 11/19/02

Go up one level in this thread


On November 19, 2002 at 14:17:42, Gian-Carlo Pascutto wrote:

>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.
>
>It seems intuitively obvious to Vincent that bitboards suck, but
>I believe neither of you.

Doesn't matter to me.  I use them.  I am happy with them.  Frans apparently
liked
them enough to convert to them.  Several others are using them with no problems.

I personally don't believe _anything_ Vincent says, but that is a different
issue.


>
>>Bitmaps seem to suffer _no_ performance penalty on
>>X86 with 32 bits, compared to 0x88.
>
>How do you determine this?

By comparing the speed I generate moves at compared to 0x88, for example?
All the "good generators" are within a factor of two or so of each other,
depending
on what they do in Make/Unmake...


>
>>Seems intuitively obvious to me that they will pick
>>up speed on a machine that does 64 bit operations.
>
>Not so obvious to me, I've posted a few issues with it
>here before.
>
>>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...
>
>Doesn't say a thing. The programs are much more different than just
>bitboard vs nonbitboard.


That's simple hand-waving.  It shows that a 64 bit program gains more from
going to a 64 bit architecture than a 32 bit program does.  I'm not about to
make
this into a computer architecture 101 discussion.  There are plenty of good
books
around that explain _exactly_ why this is true.  I don't see any nead to repeat
those
arguments over and over...

If you don't want to believe them, feel free.  It must mean _everybody_ in the
computer
architecture field is wrong, however...




>
>--
>GCP



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