Author: Bruce Moreland
Date: 17:28:56 02/28/00
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On February 28, 2000 at 17:04:13, William Bryant wrote: >I am curious, >do you hash a different constant for each of the 16 possible ep squares, or >simply a single constant if ep is possible. > >I have sixteen different values that are XOR'ed into the hash signature >depending on which square is the ep square. > >It is intersting that Bruce made a comment about this a while back. He noted >that the same opening position reached by a different order of moves will >produce a different hash signature doing ep squares in this way. Therefore it >does create a degree of inefficiency because (except for the ep move) the rest >of the position may have already been evaluated and in the hash table. > >William >wbryant@ix.netcom.com If you hash in en-passant square mindlessly you get a surprising amount of hash inefficiency. 1. e4 e5 2. c4 and 1. c4 e5 2. e4 produce the same position, and an en-passant capture is not possible in either. Yet I bet that some people hash in the d-file code in the first case and the e-file code in the second case. I found that it made more sense to check for an adjacent pawn. In that case the en-passant capture is at least pseudo-legal. bruce
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