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Subject: Bitboards, 32-bit and 64-bit cpus

Author: Gian-Carlo Pascutto

Date: 03:24:23 05/26/01

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On May 25, 2001 at 19:09:46, Slater Wold wrote:

>Of course the 64 bit processors will be faster!  Hyatt has said before, it a
>bitboard application, it will double the speed.

Currently, Crafty manipulates 64-bit entities via 32-bits insns.

Today top CPU's can manipulate 3 32-bit insns per cycle maximum.
This translates (simplified, yes) into 1.5 bitboard operations per
cycle.

However, an Athlon can also manipulate 2 64-bit entities and 2
32-bit per cycle instead. That would be 3 bitboard operations per
cycle (doubles speed). However, this would require recoding Crafty
in a mix of MMX and integer code. Not only would it make
porting Crafty impossible, it will make your head hurt. I have done
_one_ function so far and it now goes 1% faster. But I can tell you
looking at 3 calculations interwinded in 2 different assembly languages
is no fun.

A full 64 bit cpu would do 3 bitboard operations maximum. This would
be no faster than what we already have. But you could rely on the
compiler to generate the code. Aaaah (big sound of relief)

>And yes, they will run our current software, however, slower than
>what a 32 bit processor will.  So there would be no point in buying
>a 64 bit processor, until programs are coded for 64 bit.

Just a correction. For most programs they wont be faster. But they
wont be slower either, provided they are just recompiled. This
is trivial if you have a free OS. Guess why Intel and AMD have made
sure GNU C support their 64 bit architectures :)

Of course, if you are stuck on an OS and with apps you can modify,
there would be little point in upgrading. Just like with the early
Pentium Pros.

>Even when Hyatt makes Crafty v31.9 ----//
>SMP version on the 64 bitprocessors,
>I still would not count on a lot of people having them.
>The 800mhz Intel Intanuim processors are $3500 a piece.

a) Crafty already fully supports 64 bit cpus, and has done
   so for a long time. It's not because Intel/AMD don't make
   them that they don't exist.

b) Prices drop. Fast.

--
GCP



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