Author: Tom Kerrigan
Date: 15:20:16 02/19/03
Go up one level in this thread
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
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