/// probe() tries to find a book move for the given position. If no move is
/// found returns MOVE_NONE. If pickBest is true returns always the highest
/// rated move, otherwise randomly chooses one, based on the move score.
public Move probe(Position pos, string fName, bool pickBest)
{
if (fName == null || (fileName != fName && !open(fName)))
{
return(MoveS.MOVE_NONE);
}
PolyglotBook.Entry e = new PolyglotBook.Entry();
UInt16 best = 0;
uint sum = 0;
Move move = MoveS.MOVE_NONE;
Key key = polyglot_key(pos);
stream.Seek(find_first(key) * SIZE_OF_BOOKENTRY, SeekOrigin.Begin);
while (read(ref e) && e.key == key)
{
best = Math.Max(best, e.count);
sum += e.count;
// Choose book move according to its score. If a move has a very
// high score it has higher probability to be choosen than a move
// with lower score. Note that first entry is always chosen.
if ((sum != 0 && ((((uint)RKiss.rand64()) % sum) < e.count)) ||
(pickBest && e.count == best))
{
move = (e.move);
}
}
if (move == 0)
{
return(MoveS.MOVE_NONE);
}
// A PolyGlot book move is encoded as follows:
//
// bit 0- 5: destination square (from 0 to 63)
// bit 6-11: origin square (from 0 to 63)
// bit 12-14: promotion piece (from KNIGHT == 1 to QUEEN == 4)
//
// Castling moves follow "king captures rook" representation. So in case book
// move is a promotion we have to convert to our representation, in all the
// other cases we can directly compare with a Move after having masked out
// the special Move's flags (bit 14-15) that are not supported by PolyGlot.
int pt = (move >> 12) & 7;
if (pt != 0)
{
move = Types.make(Types.from_sq(move), Types.to_sq(move), MoveTypeS.PROMOTION, (pt + 1));
}
// Add 'special move' flags and verify it is legal
for (MoveList ml = new MoveList(pos, GenTypeS.LEGAL); ml.mlist[ml.cur].move != MoveS.MOVE_NONE; ++ml)
{
if (move == (ml.move() ^ Types.type_of_move(ml.move())))
{
return(ml.move());
}
}
return(MoveS.MOVE_NONE);
}
