Author: Will Singleton
Date: 17:18:51 03/06/98
I'm having trouble getting transposition tables to work in my program.
Part of the problem is the spaghetti code, but I'd like to make sure I
understand the basics before going further. Any comments would be
appreciated.
The following has been taken from various publications and source code:
I generate an array of random numbers that are associated with each
piece-square combination. The array is 12 * 64 entries, 32-bit uints.
The array is referenced by rand_num = rand_array [piece][square]. Then
all the values are XOR'd together to get the hash_key, using only the
occupied squares. Other random nums are used to represent ep_status and
castling.
The low-order 18 bits of the 32-bit key are used to generate the index
into the hash table. Store the hash key, along with depth, score,
move#, valid_flag, and the move itself. I use two hash tables, one for
each color, each 262k entries.
At new_game, zero the hash table, generate the hashkey, and then for
each move, update it. hashkey = (hashkey ^ from pc_sq) ^ to pc_sq.
---- Before generating moves, probe the table ----
address = hashkey & 0x0003ffff;
if (tt_table [plylevel % 2][address].hashlock == hashkey)
if (table_depth >= plylevel)
see if score is true score, or upper/lower bound (from cutoff)
if true score, return
if upper/lower, compare to beta for cutoff
else try move
---- After unmake move, store to the table ----
if (cutoff or bestmove)
if (tt_table depth <= plylevel)
store to the table, setting valid flag to upper/lower or true
score
-----------------------------------
Question: some have said that storing positions from the leaf nodes is
not so good, since it fills the table with sometimes irrelevant data.
What about that, and how about using the tables in the qsearch?
Help would be appreciated, as always.
Will
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