Author: Robert Hyatt
Date: 17:32:10 02/19/03
Go up one level in this thread
On February 19, 2003 at 18:20:16, Tom Kerrigan wrote: >On February 19, 2003 at 02:53:13, Matt Taylor wrote: > >>On February 18, 2003 at 13:33:12, Tom Kerrigan wrote: >> >>>On February 16, 2003 at 03:03:03, Matt Taylor wrote: >>> >>>>On February 15, 2003 at 21:28:39, Tom Kerrigan wrote: >>>> >>>>>They are if they better represent computer chess than Crafty does. I'd bet most >>>>>chess programs out there don't use bitboards (i.e., 64 bit operations) or use >>>>>bitboards less than Crafty. Bitboards are almost certainly the reason why Crafty >>>>>performs well on I2 vs. the P4. >>>>Perhaps it is, perhaps it isn't. Athlon is much more efficient with 64-bit >>>>operations than Pentium 4 is, and the Athlon isn't pulling ahead by huge strides >>>>(in Crafty). >>> >>>How do you figure the Athlon is more efficient? And what do you mean by >>>operations? ANDing, ORing, etc.? How about loading, shifting, BSF, popcount, >>>etc.? >> >>How about faster in MMX, faster in shifting, and faster in arithmetic? An MMX >>implementation will be slower on the Pentium 4. Code written in C to do the >>equivalent will involve much shifting and arithmetic which will also be slower >>on the Pentium 4. As far as I can tell, the bsf instruction on P4 is not really >>any faster than Athlon's, but it is hard to say. >> >>Logical ops have equal cycle counts on both processors making the P4's higher >>clockrate advantageous; however, logical ops are hardly the only bitboard >>manipulations. > >So the Athlon is much faster, except that it's the same for logical ops and bsf. >And we apparently don't know if Crafty uses MMX, where the Athlon would have an >advantage (what are the latencies of 64-bit MMX shifts on each chip?), or if it >breaks the bitboards into 32 bit numbers and does "normal" operations on them, >in which case I don't see why the Athlon would be any faster than the P4. (I'd >be surprised if anything gets shifted by very much in Crafty so the P4's lack of >a wide barrel shifter is probably not a handicap.) > >-Tom Pawn move generation is nothing but shifts, for example. detecting pawn rams uses a shift/and pair. It isn't a major part of things, but it is a part nonetheless... I'm sure there are others, such as detecting blockaded pawns, that I forgot...
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