Author: Robert Hyatt
Date: 08:28:57 08/20/98
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On August 20, 1998 at 10:58:28, Peter Fendrich wrote: >On August 19, 1998 at 22:58:12, Ernst A. Heinz wrote: > >>On August 19, 1998 at 15:27:10, Peter Fendrich wrote: >>> >>>continuing from Part1... >>> >>>Method C (The Hacker trick without loops. Used by DarkThought) >> >>Peter, >> >>"DarkThought" is surely not the only one to use this famous HACKMEM trick. >>But my article about "How DarkThought plays chess" explicitly mentions your >>method A, too. The looping scheme is known to produce the best results >>for sparsely populated bitboards. Therefore, we use normal and sparse >>popcount functions/macros at different places in the code depending on the >>expected population density of 1-bits. In the static evaluation function >>the density is mostly low such that we use the sparse scheme there. During >>move generation, however, you often encounter biboards that benefit a lot >>from the HACKMEM scheme because they are heavily populated with 1-bits. >> >>=Ernst= > >I've never seen the algorithm before I read about it in the DarkThought article >in ICCA Journal (or was it in you hompage? I don't remember). >It seems to be a good approach you have but I don't count bits at all in move >generation. What do you use it there for? >//Peter if you like this kind of bit-twiddling nonsense, you need to acquire a friend at the NSA or some equivalent agency. :) That is but one of a half-dozen of the most bizarre pieces of code I've ever seen, although the approach Ernst uses is actually quite old and well-known. The oddest case is a combination of the "parallel sum" approach mixed with a modulus with a bizarre constant to get the number of 1 bits... I can't find these things right now... I'll see if I can however. But for folks that are "demented" in the way they twiddle bits, you can't beat the "code breakers" at NSA. :) I asked a friend there for a suggestion once upon a time and got several back. I asked him how it felt to program while using LSD... he knew what I meant too.. :)
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