Author: Robert Hyatt
Date: 17:07:01 05/06/04
Go up one level in this thread
On May 06, 2004 at 17:12:58, Gerd Isenberg wrote: >On May 06, 2004 at 17:07:53, Gerd Isenberg wrote: > >>On May 06, 2004 at 17:03:56, Robert Hyatt wrote: >> >>>On May 06, 2004 at 16:59:57, Sune Fischer wrote: >>> >>>>On May 06, 2004 at 16:07:16, Robert Hyatt wrote: >>>> >>>>>On May 06, 2004 at 13:00:06, Mathieu Pagé wrote: >>>>> >>>>>>Hi, >>>>>> >>>>>> Actualy my engine use pre-calculated bitboards to generate the moves. and I was >>>>>>asking myself if compressing them, in order to keep them in cache would make my >>>>>>move generator faster. I tought about two techniques to compress them. >>>>>> >>>>>>1. Use a 7 bits mask as a representation of the occupancy of the line as we >>>>>>always know that the position where the piece that we want to move is occupied. >>>>>>I already use this and it cut the space used by the index by a factor of two. >>>>>>I'm sure you were all aware of this trick. >>>>> >>>>>What about using a 5-bit mask then. You don't need the two endpoint bits anyway >>>>>as you attack those squares whether they are occupied or not. >>>> >>>>What if the square is on the edge and thus already removed? >>>>Seems you end up with some being 5 bit and some being 6 bit lines. >>> >>> >>>Doesn't matter. Remember that you already know whether you are on the edge or >>>not. The only thing that matters is the occupied squares between the two >>>extreme points. That is why I currently use 6 bits. But by removing the bit >>>for the piece being tested, that would/could drop to 5. >>> > >For a rook on a1 you really need six squares from b1 to g1, to decide whether h1 >is attacked or not ;-) > OK. I see what Sune and you are talking about. I only use 6 bit indices everywhere which works just fine. 5 would be quirky when the missing bit is on the end... > > > >>> >>>> >>>>>I use 6 bit myself as squeezing out the square the piece is on is not >>>>>convenient... >>>> >>>>-S.
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