| """uint16 move encoding shared by the 2a scan and the 2b filter. |
| |
| A chess move is stored as a single uint16: |
| |
| bits 0-5 from_square (0-63) |
| bits 6-11 to_square (0-63) |
| bits 12-14 promotion (0 = none, 1 = N, 2 = B, 3 = R, 4 = Q) |
| |
| Max encodable value is 20479, so ids >= 20480 are free for special tokens. |
| |
| Piece type is deliberately *not* stored. It is always recoverable by replaying |
| the move sequence from the initial position, and the factorized decoder needs |
| it as a derived quantity anyway. Storing it would cost bytes for no information. |
| |
| Castling is encoded from the underlying king move (e1->g1), not from the "O-O" |
| text, so it round-trips like any other move. |
| """ |
|
|
| import chess |
|
|
| PROMO_TO_CODE = {None: 0, chess.KNIGHT: 1, chess.BISHOP: 2, chess.ROOK: 3, chess.QUEEN: 4} |
| CODE_TO_PROMO = {v: k for k, v in PROMO_TO_CODE.items()} |
|
|
| MAX_MOVE_ID = 20479 |
| TOK_EOS = 65535 |
|
|
|
|
| def encode(move: chess.Move) -> int: |
| return move.from_square | (move.to_square << 6) | (PROMO_TO_CODE[move.promotion] << 12) |
|
|
|
|
| def decode(code: int) -> chess.Move: |
| return chess.Move(code & 0x3F, (code >> 6) & 0x3F, CODE_TO_PROMO[(code >> 12) & 0x7]) |
|
|
