Author: Anthony Cozzie
Date: 06:07:13 09/03/03
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On September 02, 2003 at 16:52:24, Dezhi Zhao wrote: >Hi! > >I know that some programmers here have played with MMX/SSE/SSE2 quite a lot. I >am wondering if the new SSE registers and xor op can beat the regular registers >in calculating the hash key that are 64 bit operations. Have anybody tried this? > >Regards, >dzhao Generally speaking the 64 bit mmx/mmx2 operations don't help chess programs because mmx is on the floating point pipe; to transfer data between the integer & floating point pipes is something like 5-10 cycles each way; or if you go through memory you have store-load stalls of a similar amount. Plus, the regular integer pipe is actually pretty fast at bitboard computations because 2 32bit ANDs can go down the pipeline together. It only makes sense if a significant amount of work is being done, like in Gerd/Steffan's floodfill routines for example. Computing the hash key is a *very* cheap operation: two (maybe 3) times per make_move, lookup a 64 bit table value and XOR. anthony
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