266 lines
8.2 KiB
Nim
266 lines
8.2 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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## Position evaluation utilities
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import board
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type
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Score* = int32
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# Stolen from https://www.chessprogramming.org/PeSTO's_Evaluation_Function
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const
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PAWN_MIDDLEGAME_SCORES: array[64, Score] = [
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0, 0, 0, 0, 0, 0, 0, 0,
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98, 134, 61, 95, 68, 126, 34, -11,
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-6, 7, 26, 31, 65, 56, 25, -20,
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-14, 13, 6, 21, 23, 12, 17, -23,
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-27, -2, -5, 12, 17, 6, 10, -25,
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-26, -4, -4, -10, 3, 3, 33, -12,
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-35, -1, -20, -23, -15, 24, 38, -22,
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0, 0, 0, 0, 0, 0, 0, 0,
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]
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PAWN_ENDGAME_SCORES: array[64, Score] = [
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0, 0, 0, 0, 0, 0, 0, 0,
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178, 173, 158, 134, 147, 132, 165, 187,
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94, 100, 85, 67, 56, 53, 82, 84,
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32, 24, 13, 5, -2, 4, 17, 17,
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13, 9, -3, -7, -7, -8, 3, -1,
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4, 7, -6, 1, 0, -5, -1, -8,
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13, 8, 8, 10, 13, 0, 2, -7,
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0, 0, 0, 0, 0, 0, 0, 0,
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]
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KNIGHT_MIDDLEGAME_SCORES: array[64, Score] = [
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-167, -89, -34, -49, 61, -97, -15, -107,
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-73, -41, 72, 36, 23, 62, 7, -17,
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-47, 60, 37, 65, 84, 129, 73, 44,
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-9, 17, 19, 53, 37, 69, 18, 22,
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-13, 4, 16, 13, 28, 19, 21, -8,
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-23, -9, 12, 10, 19, 17, 25, -16,
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-29, -53, -12, -3, -1, 18, -14, -19,
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-105, -21, -58, -33, -17, -28, -19, -23,
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]
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KNIGHT_ENDGAME_SCORES: array[64, Score] = [
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-58, -38, -13, -28, -31, -27, -63, -99,
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-25, -8, -25, -2, -9, -25, -24, -52,
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-24, -20, 10, 9, -1, -9, -19, -41,
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-17, 3, 22, 22, 22, 11, 8, -18,
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-18, -6, 16, 25, 16, 17, 4, -18,
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-23, -3, -1, 15, 10, -3, -20, -22,
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-42, -20, -10, -5, -2, -20, -23, -44,
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-29, -51, -23, -15, -22, -18, -50, -64,
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]
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BISHOP_MIDDLEGAME_SCORES: array[64, Score] = [
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-29, 4, -82, -37, -25, -42, 7, -8,
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-26, 16, -18, -13, 30, 59, 18, -47,
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-16, 37, 43, 40, 35, 50, 37, -2,
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-4, 5, 19, 50, 37, 37, 7, -2,
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-6, 13, 13, 26, 34, 12, 10, 4,
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0, 15, 15, 15, 14, 27, 18, 10,
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4, 15, 16, 0, 7, 21, 33, 1,
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-33, -3, -14, -21, -13, -12, -39, -21,
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]
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BISHOP_ENDGAME_SCORES: array[64, Score] = [
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-14, -21, -11, -8, -7, -9, -17, -24,
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-8, -4, 7, -12, -3, -13, -4, -14,
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2, -8, 0, -1, -2, 6, 0, 4,
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-3, 9, 12, 9, 14, 10, 3, 2,
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-6, 3, 13, 19, 7, 10, -3, -9,
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-12, -3, 8, 10, 13, 3, -7, -15,
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-14, -18, -7, -1, 4, -9, -15, -27,
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-23, -9, -23, -5, -9, -16, -5, -17,
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]
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ROOK_MIDDLEGAME_SCORES: array[64, Score] = [
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32, 42, 32, 51, 63, 9, 31, 43,
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27, 32, 58, 62, 80, 67, 26, 44,
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-5, 19, 26, 36, 17, 45, 61, 16,
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-24, -11, 7, 26, 24, 35, -8, -20,
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-36, -26, -12, -1, 9, -7, 6, -23,
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-45, -25, -16, -17, 3, 0, -5, -33,
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-44, -16, -20, -9, -1, 11, -6, -71,
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-19, -13, 1, 17, 16, 7, -37, -26,
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]
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ROOK_ENDGAME_SCORES: array[64, Score] = [
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13, 10, 18, 15, 12, 12, 8, 5,
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11, 13, 13, 11, -3, 3, 8, 3,
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7, 7, 7, 5, 4, -3, -5, -3,
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4, 3, 13, 1, 2, 1, -1, 2,
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3, 5, 8, 4, -5, -6, -8, -11,
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-4, 0, -5, -1, -7, -12, -8, -16,
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-6, -6, 0, 2, -9, -9, -11, -3,
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-9, 2, 3, -1, -5, -13, 4, -20,
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]
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QUEEN_MIDDLEGAME_SCORES: array[64, Score] = [
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-28, 0, 29, 12, 59, 44, 43, 45,
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-24, -39, -5, 1, -16, 57, 28, 54,
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-13, -17, 7, 8, 29, 56, 47, 57,
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-27, -27, -16, -16, -1, 17, -2, 1,
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-9, -26, -9, -10, -2, -4, 3, -3,
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-14, 2, -11, -2, -5, 2, 14, 5,
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-35, -8, 11, 2, 8, 15, -3, 1,
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-1, -18, -9, 10, -15, -25, -31, -50,
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]
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QUEEN_ENDGAME_SCORES: array[64, Score] = [
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-9, 22, 22, 27, 27, 19, 10, 20,
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-17, 20, 32, 41, 58, 25, 30, 0,
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-20, 6, 9, 49, 47, 35, 19, 9,
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3, 22, 24, 45, 57, 40, 57, 36,
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-18, 28, 19, 47, 31, 34, 39, 23,
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-16, -27, 15, 6, 9, 17, 10, 5,
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-22, -23, -30, -16, -16, -23, -36, -32,
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-33, -28, -22, -43, -5, -32, -20, -41,
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]
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KING_MIDDLEGAME_SCORES: array[64, Score] = [
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-65, 23, 16, -15, -56, -34, 2, 13,
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29, -1, -20, -7, -8, -4, -38, -29,
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-9, 24, 2, -16, -20, 6, 22, -22,
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-17, -20, -12, -27, -30, -25, -14, -36,
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-49, -1, -27, -39, -46, -44, -33, -51,
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-14, -14, -22, -46, -44, -30, -15, -27,
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1, 7, -8, -64, -43, -16, 9, 8,
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-15, 36, 12, -54, 8, -28, 24, 14,
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]
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KING_ENDGAME_SCORES: array[64, Score] = [
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-74, -35, -18, -18, -11, 15, 4, -17,
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-12, 17, 14, 17, 17, 38, 23, 11,
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10, 17, 23, 15, 20, 45, 44, 13,
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-8, 22, 24, 27, 26, 33, 26, 3,
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-18, -4, 21, 24, 27, 23, 9, -11,
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-19, -3, 11, 21, 23, 16, 7, -9,
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-27, -11, 4, 13, 14, 4, -5, -17,
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-53, -34, -21, -11, -28, -14, -24, -43
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]
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MIDDLEGAME_TABLES: array[6, array[64, Score]] = [
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BISHOP_MIDDLEGAME_SCORES,
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KING_MIDDLEGAME_SCORES,
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KNIGHT_MIDDLEGAME_SCORES,
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PAWN_MIDDLEGAME_SCORES,
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QUEEN_MIDDLEGAME_SCORES,
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ROOK_MIDDLEGAME_SCORES
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]
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ENDGAME_TABLES: array[6, array[64, Score]] = [
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BISHOP_ENDGAME_SCORES,
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KING_ENDGAME_SCORES,
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KNIGHT_ENDGAME_SCORES,
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PAWN_ENDGAME_SCORES,
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QUEEN_ENDGAME_SCORES,
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ROOK_ENDGAME_SCORES
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]
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proc getPieceValue(kind: PieceKind): Score =
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## Returns the absolute value of a piece
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case kind:
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of Pawn:
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return Score(100)
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of Bishop:
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return Score(330)
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of Knight:
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return Score(280)
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of Rook:
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return Score(525)
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of Queen:
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return Score(950)
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else:
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discard
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proc getPieceScore*(board: Chessboard, square: Square): Score =
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## Returns the value of the piece located at
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## the given square
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return board.getPiece(square).kind.getPieceValue()
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proc getGamePhase(board: Chessboard): int =
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## Computes the game phase according to
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## how many pieces are left on the board
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result = 0
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for sq in board.getOccupancy():
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case board.getPiece(sq).kind:
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of Bishop, Knight:
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inc(result)
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of Queen:
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inc(result, 4)
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of Rook:
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inc(result, 2)
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else:
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discard
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# Caps the value in case of early
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# promotions
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result = min(24, result)
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proc evaluatePiecePositions(board: ChessBoard): Score =
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## Returns the evaluation of the current
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## material's position relative to white
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let
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middleGamePhase = board.getGamePhase()
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endGamePhase = 24 - middleGamePhase
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var
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# White, Black
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middleGameScores: array[2, Score] = [0, 0]
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endGameScores: array[2, Score] = [0, 0]
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for sq in board.getOccupancy():
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let piece = board.getPiece(sq)
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middleGameScores[piece.color.int] += MIDDLEGAME_TABLES[piece.kind.int][sq.int]
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endGameScores[piece.color.int] += ENDGAME_TABLES[piece.kind.int][sq.int]
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let
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sideToMove = board.position.sideToMove
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nonSideToMove = sideToMove.opposite()
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middleGameScore = middleGameScores[sideToMove.int] - middleGameScores[nonSideToMove.int]
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endGameScore = endGameScores[sideToMove.int] - endGameScores[nonSideToMove.int]
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result = Score((middleGameScore * middleGamePhase + endGameScore * endGamePhase) div 24)
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proc evaluateMaterial(board: ChessBoard): Score =
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## Returns the material evaluation of the
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## current position relative to white (positive
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## if in white's favor, negative otherwise)
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var
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whiteScore: Score
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blackScore: Score
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for sq in board.getOccupancyFor(White):
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whiteScore += board.getPieceScore(sq)
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for sq in board.getOccupancyFor(Black):
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blackScore += board.getPieceScore(sq)
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result = whiteScore - blackScore
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if board.position.sideToMove == Black:
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result *= -1
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proc evaluate*(board: Chessboard): Score =
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## Evaluates the current position
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result = board.evaluateMaterial()
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result += board.evaluatePiecePositions() |