Author: Guido Schimmels
Date: 04:02:57 06/12/98
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On June 10, 1998 at 13:59:09, Bruce Moreland wrote: >... >I made a single array, which is sized at max depth squared, plus max >depth, all over two ( (D^2+D)/2 ). > >I made an another array of pointers into this array, there are max depth >pointers. > >I then initialized the pointers so that the first one points at element >0, the second one points at element D, the third points at element 2D-1, >the fourth points at element 3D-2, etc. > >The point is that each of these arrays needs one less element, because >the maximum length of the PV is shorter the deeper you already are. >Levy calls this a triangular array, which seems reasonable to me. > >I was being anal about memory at the time. If you want, you can just >make an array that is D^2 and forget about it, it's not like we have to >worry about blowing RAM much these days, except with hash tables. >bruce Exactly what I was doing for years :) But it has become obsolete, as I now get the PV from a special backup table. When I get a fail high/low on those positions later in the search, I will not erase this information, but will store the new score along with it's depth and move in additional fields of this special table, so I never forget which positions where PV once and often have two or three moves in the table to use for sorting. >Another thing is that if you fail high at depth zero, you can stick the >move you failed high on in the array, and then just terminate it at >length 1, so you will have return a PV of sorts if you are in a >fail-high state. >Remember also that your array length can be undefined if you fail low. >I actually spend some energy trying to make sure that what's in the array is something reasonable. >If I fail high on the move that had been the PV up until now, I don't >kill the old PV, I let it sit in there, so I can be sure to search it >first when I re-search. >Also, if I fail low, I keep the old PV around, since it's the best thing >I have. >If I fail high on a new move, then fail low on the re-search, I put the >PV from before the fail high back, but this is a serious decision and >some would argue that this is wrong, and this doesn't pertain directly >to this topic anyway. Example from my PV table: pv_score = 100 pv_move = e2e4 pv_depth = 5 all_score = 80 all_move = d2d4 all_depth = 6 cut_score = 90 cut_move = e2e4 cut_depth = 4 In my example the question about move sorting is, try d2d4 first, which failed low last time, or e2e4 which was a PV move before that ? You have experimented with those kind of stuff as I can see from the above. Any Suggestions ? - Guido
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