On Wed, 2007-02-07 at 16:17 -0500, Don Dailey wrote:
> I have a hash funciton that creates a 64 bit "cannonical" hash of
> the position. The same hash is produced after a rotation for
> example. A book entry is a record with 3 fields, a priority
> value (how many times the deep search selected this position),
> the cannonical hash of the parent position and the cannonical
> hash of the posiiton AFTER the move is played. This makes
> collision very unlikely. The cannonical hash takes into
> consideration simple ko, so if a ko is possible it will hash
> differently than the same position where the ko is illegal.
Here is some more detail to make this clearer:
typedef struct
{
int count; // number of times this position/response seen
(priority)
u64 key; // cannonical position key
u64 resp; // resulting cannonical position
} book_entry;
These book_entry records are stored in a file and I keep them
sorted. So the procedure to see if there is a book move is
to binary search the file on the parent position key,
collect all of these records together (making sure there is a
legal move which leads to the cannonical response key) and then
choose one of the available moves in proportion to the
priority values (the count field.)
- Don
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