439 lines
18 KiB
Python
439 lines
18 KiB
Python
#!/usr/bin/env pypy
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# -*- coding: utf-8 -*-
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from __future__ import print_function
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import re, sys, time
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from itertools import count
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from collections import namedtuple
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###############################################################################
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# Piece-Square tables. Tune these to change sunfish's behaviour
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###############################################################################
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piece = { 'P': 100, 'N': 280, 'B': 320, 'R': 479, 'Q': 929, 'K': 60000 }
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pst = {
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'P': ( 0, 0, 0, 0, 0, 0, 0, 0,
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78, 83, 86, 73, 102, 82, 85, 90,
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7, 29, 21, 44, 40, 31, 44, 7,
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-17, 16, -2, 15, 14, 0, 15, -13,
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-26, 3, 10, 9, 6, 1, 0, -23,
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-22, 9, 5, -11, -10, -2, 3, -19,
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-31, 8, -7, -37, -36, -14, 3, -31,
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0, 0, 0, 0, 0, 0, 0, 0),
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'N': ( -66, -53, -75, -75, -10, -55, -58, -70,
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-3, -6, 100, -36, 4, 62, -4, -14,
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10, 67, 1, 74, 73, 27, 62, -2,
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24, 24, 45, 37, 33, 41, 25, 17,
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-1, 5, 31, 21, 22, 35, 2, 0,
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-18, 10, 13, 22, 18, 15, 11, -14,
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-23, -15, 2, 0, 2, 0, -23, -20,
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-74, -23, -26, -24, -19, -35, -22, -69),
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'B': ( -59, -78, -82, -76, -23,-107, -37, -50,
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-11, 20, 35, -42, -39, 31, 2, -22,
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-9, 39, -32, 41, 52, -10, 28, -14,
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25, 17, 20, 34, 26, 25, 15, 10,
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13, 10, 17, 23, 17, 16, 0, 7,
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14, 25, 24, 15, 8, 25, 20, 15,
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19, 20, 11, 6, 7, 6, 20, 16,
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-7, 2, -15, -12, -14, -15, -10, -10),
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'R': ( 35, 29, 33, 4, 37, 33, 56, 50,
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55, 29, 56, 67, 55, 62, 34, 60,
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19, 35, 28, 33, 45, 27, 25, 15,
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0, 5, 16, 13, 18, -4, -9, -6,
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-28, -35, -16, -21, -13, -29, -46, -30,
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-42, -28, -42, -25, -25, -35, -26, -46,
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-53, -38, -31, -26, -29, -43, -44, -53,
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-30, -24, -18, 5, -2, -18, -31, -32),
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'Q': ( 6, 1, -8,-104, 69, 24, 88, 26,
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14, 32, 60, -10, 20, 76, 57, 24,
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-2, 43, 32, 60, 72, 63, 43, 2,
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1, -16, 22, 17, 25, 20, -13, -6,
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-14, -15, -2, -5, -1, -10, -20, -22,
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-30, -6, -13, -11, -16, -11, -16, -27,
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-36, -18, 0, -19, -15, -15, -21, -38,
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-39, -30, -31, -13, -31, -36, -34, -42),
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'K': ( 4, 54, 47, -99, -99, 60, 83, -62,
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-32, 10, 55, 56, 56, 55, 10, 3,
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-62, 12, -57, 44, -67, 28, 37, -31,
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-55, 50, 11, -4, -19, 13, 0, -49,
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-55, -43, -52, -28, -51, -47, -8, -50,
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-47, -42, -43, -79, -64, -32, -29, -32,
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-4, 3, -14, -50, -57, -18, 13, 4,
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17, 30, -3, -14, 6, -1, 40, 18),
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}
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# Pad tables and join piece and pst dictionaries
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for k, table in pst.items():
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padrow = lambda row: (0,) + tuple(x+piece[k] for x in row) + (0,)
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pst[k] = sum((padrow(table[i*8:i*8+8]) for i in range(8)), ())
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pst[k] = (0,)*20 + pst[k] + (0,)*20
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###############################################################################
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# Global constants
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###############################################################################
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# Our board is represented as a 120 character string. The padding allows for
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# fast detection of moves that don't stay within the board.
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A1, H1, A8, H8 = 91, 98, 21, 28
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initial = (
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' \n' # 0 - 9
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' \n' # 10 - 19
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' rnbqkbnr\n' # 20 - 29
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' pppppppp\n' # 30 - 39
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' ........\n' # 40 - 49
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' ........\n' # 50 - 59
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' ........\n' # 60 - 69
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' ........\n' # 70 - 79
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' PPPPPPPP\n' # 80 - 89
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' RNBQKBNR\n' # 90 - 99
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' \n' # 100 -109
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' \n' # 110 -119
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)
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# Lists of possible moves for each piece type.
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N, E, S, W = -10, 1, 10, -1
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directions = {
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'P': (N, N+N, N+W, N+E),
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'N': (N+N+E, E+N+E, E+S+E, S+S+E, S+S+W, W+S+W, W+N+W, N+N+W),
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'B': (N+E, S+E, S+W, N+W),
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'R': (N, E, S, W),
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'Q': (N, E, S, W, N+E, S+E, S+W, N+W),
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'K': (N, E, S, W, N+E, S+E, S+W, N+W)
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}
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# Mate value must be greater than 8*queen + 2*(rook+knight+bishop)
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# King value is set to twice this value such that if the opponent is
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# 8 queens up, but we got the king, we still exceed MATE_VALUE.
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# When a MATE is detected, we'll set the score to MATE_UPPER - plies to get there
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# E.g. Mate in 3 will be MATE_UPPER - 6
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MATE_LOWER = piece['K'] - 10*piece['Q']
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MATE_UPPER = piece['K'] + 10*piece['Q']
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# The table size is the maximum number of elements in the transposition table.
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TABLE_SIZE = 1e7
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# Constants for tuning search
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QS_LIMIT = 219
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EVAL_ROUGHNESS = 13
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DRAW_TEST = True
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###############################################################################
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# Chess logic
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###############################################################################
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class Position(namedtuple('Position', 'board score wc bc ep kp')):
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""" A state of a chess game
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board -- a 120 char representation of the board
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score -- the board evaluation
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wc -- the castling rights, [west/queen side, east/king side]
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bc -- the opponent castling rights, [west/king side, east/queen side]
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ep - the en passant square
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kp - the king passant square
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"""
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def gen_moves(self):
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# For each of our pieces, iterate through each possible 'ray' of moves,
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# as defined in the 'directions' map. The rays are broken e.g. by
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# captures or immediately in case of pieces such as knights.
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for i, p in enumerate(self.board):
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if not p.isupper(): continue
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for d in directions[p]:
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for j in count(i+d, d):
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q = self.board[j]
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# Stay inside the board, and off friendly pieces
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if q.isspace() or q.isupper(): break
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# Pawn move, double move and capture
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if p == 'P' and d in (N, N+N) and q != '.': break
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if p == 'P' and d == N+N and (i < A1+N or self.board[i+N] != '.'): break
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if p == 'P' and d in (N+W, N+E) and q == '.' \
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and j not in (self.ep, self.kp, self.kp-1, self.kp+1): break
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# Move it
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yield (i, j)
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# Stop crawlers from sliding, and sliding after captures
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if p in 'PNK' or q.islower(): break
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# Castling, by sliding the rook next to the king
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if i == A1 and self.board[j+E] == 'K' and self.wc[0]: yield (j+E, j+W)
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if i == H1 and self.board[j+W] == 'K' and self.wc[1]: yield (j+W, j+E)
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def rotate(self):
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''' Rotates the board, preserving enpassant '''
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return Position(
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self.board[::-1].swapcase(), -self.score, self.bc, self.wc,
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119-self.ep if self.ep else 0,
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119-self.kp if self.kp else 0)
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def nullmove(self):
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''' Like rotate, but clears ep and kp '''
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return Position(
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self.board[::-1].swapcase(), -self.score,
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self.bc, self.wc, 0, 0)
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def move(self, move):
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i, j = move
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p, q = self.board[i], self.board[j]
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put = lambda board, i, p: board[:i] + p + board[i+1:]
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# Copy variables and reset ep and kp
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board = self.board
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wc, bc, ep, kp = self.wc, self.bc, 0, 0
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score = self.score + self.value(move)
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# Actual move
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board = put(board, j, board[i])
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board = put(board, i, '.')
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# Castling rights, we move the rook or capture the opponent's
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if i == A1: wc = (False, wc[1])
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if i == H1: wc = (wc[0], False)
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if j == A8: bc = (bc[0], False)
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if j == H8: bc = (False, bc[1])
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# Castling
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if p == 'K':
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wc = (False, False)
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if abs(j-i) == 2:
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kp = (i+j)//2
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board = put(board, A1 if j < i else H1, '.')
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board = put(board, kp, 'R')
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# Pawn promotion, double move and en passant capture
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if p == 'P':
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if A8 <= j <= H8:
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board = put(board, j, 'Q')
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if j - i == 2*N:
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ep = i + N
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if j == self.ep:
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board = put(board, j+S, '.')
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# We rotate the returned position, so it's ready for the next player
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return Position(board, score, wc, bc, ep, kp).rotate()
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def value(self, move):
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i, j = move
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p, q = self.board[i], self.board[j]
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# Actual move
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score = pst[p][j] - pst[p][i]
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# Capture
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if q.islower():
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score += pst[q.upper()][119-j]
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# Castling check detection
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if abs(j-self.kp) < 2:
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score += pst['K'][119-j]
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# Castling
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if p == 'K' and abs(i-j) == 2:
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score += pst['R'][(i+j)//2]
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score -= pst['R'][A1 if j < i else H1]
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# Special pawn stuff
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if p == 'P':
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if A8 <= j <= H8:
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score += pst['Q'][j] - pst['P'][j]
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if j == self.ep:
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score += pst['P'][119-(j+S)]
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return score
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###############################################################################
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# Search logic
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###############################################################################
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# lower <= s(pos) <= upper
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Entry = namedtuple('Entry', 'lower upper')
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class Searcher:
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def __init__(self):
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self.tp_score = {}
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self.tp_move = {}
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self.history = set()
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self.nodes = 0
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def bound(self, pos, gamma, depth, root=True):
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""" returns r where
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s(pos) <= r < gamma if gamma > s(pos)
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gamma <= r <= s(pos) if gamma <= s(pos)"""
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self.nodes += 1
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# Depth <= 0 is QSearch. Here any position is searched as deeply as is needed for
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# calmness, and from this point on there is no difference in behaviour depending on
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# depth, so so there is no reason to keep different depths in the transposition table.
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depth = max(depth, 0)
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# Sunfish is a king-capture engine, so we should always check if we
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# still have a king. Notice since this is the only termination check,
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# the remaining code has to be comfortable with being mated, stalemated
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# or able to capture the opponent king.
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if pos.score <= -MATE_LOWER:
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return -MATE_UPPER
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# We detect 3-fold captures by comparing against previously
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# _actually played_ positions.
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# Note that we need to do this before we look in the table, as the
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# position may have been previously reached with a different score.
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# This is what prevents a search instability.
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# FIXME: This is not true, since other positions will be affected by
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# the new values for all the drawn positions.
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if DRAW_TEST:
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if not root and pos in self.history:
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return 0
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# Look in the table if we have already searched this position before.
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# We also need to be sure, that the stored search was over the same
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# nodes as the current search.
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entry = self.tp_score.get((pos, depth, root), Entry(-MATE_UPPER, MATE_UPPER))
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if entry.lower >= gamma and (not root or self.tp_move.get(pos) is not None):
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return entry.lower
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if entry.upper < gamma:
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return entry.upper
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# Here extensions may be added
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# Such as 'if in_check: depth += 1'
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# Generator of moves to search in order.
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# This allows us to define the moves, but only calculate them if needed.
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def moves():
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# First try not moving at all. We only do this if there is at least one major
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# piece left on the board, since otherwise zugzwangs are too dangerous.
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if depth > 0 and not root and any(c in pos.board for c in 'RBNQ'):
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yield None, -self.bound(pos.nullmove(), 1-gamma, depth-3, root=False)
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# For QSearch we have a different kind of null-move, namely we can just stop
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# and not capture anything else.
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if depth == 0:
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yield None, pos.score
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# Then killer move. We search it twice, but the tp will fix things for us.
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# Note, we don't have to check for legality, since we've already done it
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# before. Also note that in QS the killer must be a capture, otherwise we
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# will be non deterministic.
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killer = self.tp_move.get(pos)
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if killer and (depth > 0 or pos.value(killer) >= QS_LIMIT):
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yield killer, -self.bound(pos.move(killer), 1-gamma, depth-1, root=False)
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# Then all the other moves
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for move in sorted(pos.gen_moves(), key=pos.value, reverse=True):
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#for val, move in sorted(((pos.value(move), move) for move in pos.gen_moves()), reverse=True):
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# If depth == 0 we only try moves with high intrinsic score (captures and
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# promotions). Otherwise we do all moves.
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if depth > 0 or pos.value(move) >= QS_LIMIT:
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yield move, -self.bound(pos.move(move), 1-gamma, depth-1, root=False)
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# Run through the moves, shortcutting when possible
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best = -MATE_UPPER
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for move, score in moves():
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best = max(best, score)
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if best >= gamma:
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# Clear before setting, so we always have a value
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if len(self.tp_move) > TABLE_SIZE: self.tp_move.clear()
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# Save the move for pv construction and killer heuristic
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self.tp_move[pos] = move
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break
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# Stalemate checking is a bit tricky: Say we failed low, because
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# we can't (legally) move and so the (real) score is -infty.
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# At the next depth we are allowed to just return r, -infty <= r < gamma,
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# which is normally fine.
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# However, what if gamma = -10 and we don't have any legal moves?
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# Then the score is actaully a draw and we should fail high!
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# Thus, if best < gamma and best < 0 we need to double check what we are doing.
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# This doesn't prevent sunfish from making a move that results in stalemate,
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# but only if depth == 1, so that's probably fair enough.
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# (Btw, at depth 1 we can also mate without realizing.)
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if best < gamma and best < 0 and depth > 0:
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is_dead = lambda pos: any(pos.value(m) >= MATE_LOWER for m in pos.gen_moves())
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if all(is_dead(pos.move(m)) for m in pos.gen_moves()):
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in_check = is_dead(pos.nullmove())
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best = -MATE_UPPER if in_check else 0
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# Clear before setting, so we always have a value
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if len(self.tp_score) > TABLE_SIZE: self.tp_score.clear()
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# Table part 2
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if best >= gamma:
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self.tp_score[pos, depth, root] = Entry(best, entry.upper)
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if best < gamma:
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self.tp_score[pos, depth, root] = Entry(entry.lower, best)
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return best
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def search(self, pos, history=()):
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""" Iterative deepening MTD-bi search """
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self.nodes = 0
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if DRAW_TEST:
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self.history = set(history)
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# print('# Clearing table due to new history')
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self.tp_score.clear()
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# In finished games, we could potentially go far enough to cause a recursion
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# limit exception. Hence we bound the ply.
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for depth in range(1, 1000):
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# The inner loop is a binary search on the score of the position.
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# Inv: lower <= score <= upper
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# 'while lower != upper' would work, but play tests show a margin of 20 plays
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# better.
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lower, upper = -MATE_UPPER, MATE_UPPER
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while lower < upper - EVAL_ROUGHNESS:
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gamma = (lower+upper+1)//2
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score = self.bound(pos, gamma, depth)
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if score >= gamma:
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lower = score
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if score < gamma:
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upper = score
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# We want to make sure the move to play hasn't been kicked out of the table,
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# So we make another call that must always fail high and thus produce a move.
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self.bound(pos, lower, depth)
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# If the game hasn't finished we can retrieve our move from the
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# transposition table.
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yield depth, self.tp_move.get(pos), self.tp_score.get((pos, depth, True)).lower
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###############################################################################
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# User interface
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###############################################################################
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def parse(c):
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fil, rank = ord(c[0]) - ord('a'), int(c[1]) - 1
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return A1 + fil - 10*rank
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def render(i):
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rank, fil = divmod(i - A1, 10)
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return chr(fil + ord('a')) + str(-rank + 1)
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def main():
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hist = [Position(initial, 0, (True,True), (True,True), 0, 0)]
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searcher = Searcher()
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while True:
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print_pos(hist[-1])
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if hist[-1].score <= -MATE_LOWER:
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print("You lost")
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break
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# We query the user until she enters a (pseudo) legal move.
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move = None
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while move not in hist[-1].gen_moves():
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match = re.match('([a-h][1-8])'*2, input('Your move: '))
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if match:
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move = parse(match.group(1)), parse(match.group(2))
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else:
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# Inform the user when invalid input (e.g. "help") is entered
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print("Please enter a move like g8f6")
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hist.append(hist[-1].move(move))
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# After our move we rotate the board and print it again.
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# This allows us to see the effect of our move.
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print_pos(hist[-1].rotate())
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if hist[-1].score <= -MATE_LOWER:
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print("You won")
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break
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# Fire up the engine to look for a move.
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start = time.time()
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for _depth, move, score in searcher.search(hist[-1], hist):
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if time.time() - start > 1:
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break
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if score == MATE_UPPER:
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print("Checkmate!")
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# The black player moves from a rotated position, so we have to
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# 'back rotate' the move before printing it.
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print("My move:", render(119-move[0]) + render(119-move[1]))
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hist.append(hist[-1].move(move))
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|
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if __name__ == '__main__':
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main()
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|