Author: Russell Reagan
Date: 17:17:36 01/13/03
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On January 13, 2003 at 18:30:05, Matt Taylor wrote: >I think the real bottleneck would be the misjudgement of the speed of MMX. It is >not as fast to respond as the integer units, though it maintains similar >throughput. Using MMX for 64-bit arithmetic is not worthwhile as the same >operations are available from the integer unit with lower setup costs. The only >advantages include a minor gain in parallelism in hand-tweaked code and >additional register space. Apparently if you use MMX correctly, it will be significantly faster than the corresponding routine written in C (if it relies on 64-bit operations). The primary example that comes to mind is that Gerd uses MMX in IsiChess to do 64-bit operations in the KoggeStone algorithms. He said it gave him a small speed increase. Compare that with the same routines written in C, and the C routines will be significantly slower. I know this because I wrote a program using those routines in C and it got about 70 knps (compare with Crafty 300-500knps), and all it did was alpha-beta, material + mobility eval, and nothing else. I tried several bitboard implementations, and the common factor in the slow ones was the C KoggeStone attack generation. Gerd didn't experience such a significant speed hit when he used his MMX routines. So it does appear that there is a misjudgement of the speed of using MMX, but I'm not sure whether it is an underestimation or overestimation.
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