83 lines
2.2 KiB
Nim
83 lines
2.2 KiB
Nim
# Copyright 2024 Mattia Giambirtone & All Contributors
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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## Implementation of Zobrist hashing
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import std/random
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import pieces
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type
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ZobristKey* = distinct uint64
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## A zobrist key
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func `xor`*(a, b: ZobristKey): ZobristKey = ZobristKey(a.uint64 xor b.uint64)
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proc computeZobristKeys: array[781, ZobristKey] =
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## Precomputes our zobrist keys
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var prng = initRand(69420) # Nice.
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# One for each piece on each square
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for i in 0..767:
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result[i] = ZobristKey(prng.next())
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# One to indicate that it is black's turn
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# to move
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result[768] = ZobristKey(prng.next())
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# Four numbers to indicate castling rights
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for i in 769..773:
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result[i] = ZobristKey(prng.next())
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# Eight numbers to indicate the file of a valid
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# En passant square, if any
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for i in 774..781:
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result[i] = ZobristKey(prng.next())
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let ZOBRIST_KEYS = computeZobristKeys()
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const PIECE_TO_INDEX = [[0, 1, 2, 3, 4, 5], [6, 7, 8, 9, 10, 11]]
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proc getKey*(piece: Piece, square: Square): ZobristKey =
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let index = PIECE_TO_INDEX[piece.color.int][piece.kind.int] + square.int
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return ZOBRIST_KEYS[index]
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proc getBlackToMoveKey*: ZobristKey = ZOBRIST_KEYS[768]
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proc getQueenSideCastlingKey*(color: PieceColor): ZobristKey =
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case color:
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of White:
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return ZOBRIST_KEYS[769]
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of Black:
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return ZOBRIST_KEYS[771]
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else:
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discard
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proc getKingSideCastlingKey*(color: PieceColor): ZobristKey =
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case color:
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of White:
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return ZOBRIST_KEYS[770]
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of Black:
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return ZOBRIST_KEYS[772]
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else:
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discard
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proc getEnPassantKey*(file: SomeInteger): ZobristKey = ZOBRIST_KEYS[774 + file] |