Author: Robert Hyatt
Date: 05:57:10 04/25/00
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On April 25, 2000 at 01:20:11, Bas Hamstra wrote: >I have some evidence that an unrotated bb approach can be as fast or faster than >a rotated one. > >- my fastest ever version did it unrotated. I thereafter thought rotated would >be even faster, but never got that speed again. (until hopefully now) > >- Dan Newman reaches almost 600k nps with little eval on a PIII/500, unrotated. >While I thought the limit (based on what I see around) for rotated on this >hardware is about 500k doing only material! > >- On this board I saw someone gen moves pretty fast unrotated. > >Pro unrotated: > >- you can gen moves in LVA/MVV order right away. You can not do that while >rotating, at least not the way Crafty does it. Saves a sort afterwards. Don't >know how big a factor this is. This is wrong. Rotated or Unrotated doesn't affect generating moves in MVV/LVA order. Dark Thought uses MVV/LVA + rotated bitboards. I tried MVV/LVA a few years ago during a discussion with Hsu in r.g.c.c... I had _no_ problems making it work. > >- You don't need the expensive 64 bit shifts doing movegeneration (and eval), >which saves a lot of overhead. > >- Your make() is much faster without the 4 Occupied maps. > >Contra: > >- You have to scan for blocks, while rotated doesn't need to. However using a >int__64 blockmask[From][To] can do this pretty quick (though some say scanning >the board is even faster). > >The big question is: is the extra overhead of rotated bb's justifyable? Could it >be non-rotated is faster overall? I don't see how. But one point is that bitboards are a 64 bit technique, but they are (at present) being used on a 32 bit architecture, which is not an optimal solution. On 64 bit architectures, this is probably the right way to do it. > >(Currently I myself have started all over trying to make a really fast rotated >BB program. Looks promising so far: make/unmake=2M/sec and movegeneration=12M >moves/sec on a Celeron 466) This is such a small part of a chess engine it doesn't really matter.
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