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Fix incremental zobrist hashing, fix repetition detection, add ttmove, wait for search thread to complete

This commit is contained in:
Mattia Giambirtone 2024-05-02 14:39:46 +02:00
parent faf64c22e1
commit a3c8eb7a35
8 changed files with 131 additions and 86 deletions
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5
Chess/nimfish/nimfishpkg/board.nim
View File

@ -87,17 +87,16 @@ proc toFEN*(self: Chessboard): string =
return self.position.toFEN()
proc drawByRepetition*(self: var Chessboard): bool =
proc drawnByRepetition*(self: Chessboard): bool =
## Returns whether the current position is a draw
## by repetition
# TODO: Improve this
var i = self.positions.high()
var count = 0
while i > 0:
while i >= 0:
if self.position.zobristKey == self.positions[i].zobristKey:
inc(count)
if count == 2:
self.position.repetitionDraw = true
return true
dec(i)

68
Chess/nimfish/nimfishpkg/movegen.nim
View File

@ -340,7 +340,10 @@ proc doMove*(self: var Chessboard, move: Move) =
self.positions.add(self.position)
# Final checks
let piece = self.position.getPiece(move.startSquare)
let
piece = self.position.getPiece(move.startSquare)
sideToMove = piece.color
nonSideToMove = sideToMove.opposite()
when not defined(danger):
doAssert piece.kind != Empty and piece.color != None, &"{move} {self.toFEN()}"
@ -369,7 +372,7 @@ proc doMove*(self: var Chessboard, move: Move) =
self.position = Position(plyFromRoot: self.position.plyFromRoot + 1,
halfMoveClock: halfMoveClock,
fullMoveCount: fullMoveCount,
sideToMove: self.position.sideToMove.opposite(),
sideToMove: nonSideToMove,
enPassantSquare: enPassantTarget,
pieces: self.position.pieces,
castlingAvailability: self.position.castlingAvailability,
@ -382,14 +385,24 @@ proc doMove*(self: var Chessboard, move: Move) =
if move.isEnPassant():
# Make the en passant pawn disappear
let epPawnSquare = move.targetSquare.toBitboard().backwardRelativeTo(piece.color).toSquare()
let epPawnSquare = move.targetSquare.toBitboard().backwardRelativeTo(sideToMove).toSquare()
self.position.zobristKey = self.position.zobristKey xor self.position.getPiece(epPawnSquare).getKey(epPawnSquare)
self.position.removePiece(epPawnSquare)
if move.isCastling() or piece.kind == King:
# If the king has moved, all castling rights for the side to
# move are revoked
self.position.castlingAvailability[piece.color] = (false, false)
if self.position.castlingAvailability[sideToMove].king:
# XOR is its own inverse, so while setting a boolean to false more than once
# is not a problem, XORing the same key twice would give back the castling
# rights to the moving side!
self.position.castlingAvailability[sideToMove].king = false
self.position.zobristKey = self.position.zobristKey xor getKingSideCastlingKey(sideToMove)
if self.position.castlingAvailability[sideToMove].queen:
self.position.castlingAvailability[sideToMove].queen = false
self.position.zobristKey = self.position.zobristKey xor getQueenSideCastlingKey(sideToMove)
if move.isCastling():
# Move the rook where it belongs
var
@ -398,26 +411,30 @@ proc doMove*(self: var Chessboard, move: Move) =
target: Square
if move.targetSquare == piece.kingSideCastling():
source = piece.color.kingSideRook()
source = sideToMove.kingSideRook()
rook = self.position.getPiece(source)
target = rook.kingSideCastling()
elif move.targetSquare == piece.queenSideCastling():
source = piece.color.queenSideRook()
source = sideToMove.queenSideRook()
rook = self.position.getPiece(source)
target = rook.queenSideCastling()
self.position.movePiece(source, target)
self.position.zobristKey = self.position.zobristKey xor piece.getKey(source)
self.position.zobristKey = self.position.zobristKey xor piece.getKey(target)
self.position.zobristKey = self.position.zobristKey xor rook.getKey(source)
self.position.zobristKey = self.position.zobristKey xor rook.getKey(target)
if piece.kind == Rook:
# If a rook on either side moves, castling rights are permanently revoked
# on that side
if move.startSquare == piece.color.kingSideRook():
self.position.castlingAvailability[piece.color].king = false
elif move.startSquare == piece.color.queenSideRook():
self.position.castlingAvailability[piece.color].queen = false
if move.startSquare == sideToMove.kingSideRook():
if self.position.castlingAvailability[sideToMove].king:
self.position.castlingAvailability[sideToMove].king = false
self.position.zobristKey = self.position.zobristKey xor getKingSideCastlingKey(sideToMove)
elif move.startSquare == sideToMove.queenSideRook():
if self.position.castlingAvailability[sideToMove].queen:
self.position.castlingAvailability[sideToMove].queen = false
self.position.zobristKey = self.position.zobristKey xor getQueenSideCastlingKey(sideToMove)
if move.isCapture():
# Get rid of captured pieces
@ -427,9 +444,13 @@ proc doMove*(self: var Chessboard, move: Move) =
# If a rook has been captured, castling on that side is prohibited
if captured.kind == Rook:
if move.targetSquare == captured.color.kingSideRook():
self.position.castlingAvailability[captured.color].king = false
if self.position.castlingAvailability[nonSideToMove].king:
self.position.castlingAvailability[nonSideToMove].king = false
self.position.zobristKey = self.position.zobristKey xor getKingSideCastlingKey(nonSideToMove)
elif move.targetSquare == captured.color.queenSideRook():
self.position.castlingAvailability[captured.color].queen = false
if self.position.castlingAvailability[nonSideToMove].queen:
self.position.castlingAvailability[nonSideToMove].queen = false
self.position.zobristKey = self.position.zobristKey xor getQueenSideCastlingKey(nonSideToMove)
# Move the piece to its target square
self.position.movePiece(move)
@ -457,12 +478,8 @@ proc doMove*(self: var Chessboard, move: Move) =
self.position.spawnPiece(move.targetSquare, spawnedPiece)
# Updates checks and pins for the (new) side to move
self.position.updateChecksAndPins()
# Last updates to zobrist key
if self.position.castlingAvailability[piece.color].king:
self.position.zobristKey = self.position.zobristKey xor getKingSideCastlingKey(piece.color)
if self.position.castlingAvailability[piece.color].queen:
self.position.zobristKey = self.position.zobristKey xor getQueenSideCastlingKey(piece.color)
discard self.drawByRepetition()
# Swap the side to move
self.position.zobristKey = self.position.zobristKey xor getBlackToMoveKey()
proc isLegal*(self: var Chessboard, move: Move): bool {.inline.} =
@ -514,9 +531,12 @@ const testFens = staticRead("../../tests/all.txt").splitLines()
proc basicTests* =
# Test the FEN parser
for fen in testFens:
doAssert fen == newChessboardFromFEN(fen).toFEN()
doAssert fen == loadFEN(fen).toFEN()
# Test zobrist hashing
for fen in testFens:
var
board = newChessboardFromFEN(fen)
@ -532,7 +552,6 @@ proc basicTests* =
doAssert not hashes.contains(key), &"{fen} has zobrist collisions {move} -> {hashes[key]} (key is {key.uint64})"
hashes[key] = move
var board = newDefaultChessboard()
# Ensure correct number of pieces
testPieceCount(board, Pawn, White, 8)
@ -619,6 +638,11 @@ proc basicTests* =
testPieceBitboard(blackQueens, blackQueenSquares)
testPieceBitboard(blackKing, blackKingSquares)
# Test repetition
for move in ["b1c3", "g8f6", "c3b1", "f6g8", "b1c3", "g8f6", "c3b1", "f6g8"]:
board.makeMove(createMove(move[0..1].toSquare(), move[2..3].toSquare()))
doAssert board.drawnByRepetition()
when isMainModule:
basicTests()

2
Chess/nimfish/nimfishpkg/position.nim
View File

@ -58,8 +58,6 @@ type
checkers*: Bitboard
# Zobrist hash of this position
zobristKey*: ZobristKey
# Cached result of drawByRepetition()
repetitionDraw*: bool
# A mailbox for fast piece lookup by
# location
mailbox*: array[Square(0)..Square(63), Piece]

70
Chess/nimfish/nimfishpkg/search.nim
View File

@ -45,14 +45,14 @@ type
currentExtensionCount: uint8
proc newSearchManager*(position: Position, transpositions: TTable): SearchManager =
proc newSearchManager*(board: Chessboard, transpositions: TTable): SearchManager =
new(result)
result.board = newChessboard()
result.board.position = position
result.board = board
result.bestMoveRoot = nullMove()
result.transpositionTable = transpositions
proc isSearching*(self: SearchManager): bool =
## Returns whether a search for the best
## move is in progress
@ -74,6 +74,10 @@ proc getEstimatedMoveScore(self: SearchManager, move: Move): Score =
nonSideToMove = sideToMove.opposite()
if self.previousBestMove != nullMove() and move == self.previousBestMove:
return highestEval() + 1
when defined(useTT):
let query = self.transpositionTable.get(self.board.position.zobristKey)
if query.success and query.entry.bestMove != nullMove() and query.entry.bestMove == move:
return highestEval() + 1
if move.isCapture():
# Implementation of MVVLVA: Most Valuable Victim Least Valuable Attacker
# We prioritize moves that capture the most valuable pieces, and as a
@ -125,7 +129,7 @@ proc log(self: SearchManager, depth: int) =
nps = 1000 * (self.nodeCount div max(elapsedMsec, 1))
var logMsg = &"info depth {depth} time {elapsedMsec} nodes {self.nodeCount} nps {nps}"
if self.bestMoveRoot != nullMove():
logMsg &= &" bestmove {self.bestMoveRoot.toAlgebraic()} score {self.bestRootScore}"
logMsg &= &" score cp {self.bestRootScore} pv {self.bestMoveRoot.toAlgebraic()}"
echo logMsg
@ -185,6 +189,8 @@ proc qsearch(self: SearchManager, ply: uint8, alpha, beta: Score): Score =
if score >= beta:
# Same as with the regular alpha-beta search
return score
if self.board.position.halfMoveClock >= 100 or self.board.drawnByRepetition():
return Score(0)
var moves = newMoveList()
self.board.generateMoves(moves, capturesOnly=true)
self.reorderMoves(moves)
@ -193,14 +199,7 @@ proc qsearch(self: SearchManager, ply: uint8, alpha, beta: Score): Score =
for move in moves:
self.board.doMove(move)
inc(self.nodeCount)
var score: Score
if self.board.position.halfMoveClock >= 100 or self.board.position.repetitionDraw:
# Drawing by repetition is *bad*
score = Score(0)
else:
# Find the best move for us (worst move
# for our opponent, hence the negative sign)
score = -self.qsearch(ply + 1, -beta, -alpha)
let score = -self.qsearch(ply + 1, -beta, -alpha)
self.board.unmakeMove()
bestScore = max(score, bestScore)
if score >= beta:
@ -223,18 +222,21 @@ proc search(self: SearchManager, depth, ply: int, alpha, beta: Score): Score {.d
# one because then we wouldn't have a move to return.
# In practice this should not be a problem
return
when defined(useTT):
let query = self.transpositionTable.get(self.board.position.zobristKey, depth.uint8)
if query.success:
case query.entry.flag:
of Exact:
return query.entry.score
of LowerBound:
if query.entry.score >= beta:
return query.entry.score
of UpperBound:
if query.entry.score <= alpha:
return query.entry.score
# when defined(useTT):
# if ply > 0:
# let query = self.transpositionTable.get(self.board.position.zobristKey, depth.uint8)
# if query.success:
# case query.entry.flag:
# of Exact:
# return query.entry.score
# of LowerBound:
# if query.entry.score >= beta:
# return query.entry.score
# of UpperBound:
# if query.entry.score <= alpha:
# return query.entry.score
if self.board.drawnByRepetition():
return Score(0)
if depth == 0:
# Quiescent search gain: 264.8 +/- 71.6
return self.qsearch(0, alpha, beta)
@ -264,23 +266,20 @@ proc search(self: SearchManager, depth, ply: int, alpha, beta: Score): Score {.d
when defined(searchExtensions):
extension = self.getSearchExtension(move)
inc(self.nodeCount)
# Find the best move for us (worst move
# for our opponent, hence the negative sign)
var score: Score
var fullDepth = true
when defined(searchLMR):
if extension == 0 and i >= 3 and not move.isCapture():
# Late Move Reduction: assume our move orderer did a good job,
# so it is not worth to look at all moves at the same depth equally.
# so it is not worth it to look at all moves at the same depth equally.
# If this move turns out to be better than we expected, we'll re-search
# it at full depth
const reduction = 1
score = -self.search(depth - 1 - reduction, ply + 1, -beta, -alpha)
fullDepth = score > alpha
if self.board.position.halfMoveClock >= 100 or self.board.position.repetitionDraw:
# Drawing by repetition is *bad*
score = Score(0)
elif fullDepth:
if fullDepth:
# Find the best move for us (worst move
# for our opponent, hence the negative sign)
score = -self.search(depth - 1 + extension, ply + 1, -beta, -alpha)
self.board.unmakeMove()
# When a search is cancelled or times out, we need
@ -289,10 +288,7 @@ proc search(self: SearchManager, depth, ply: int, alpha, beta: Score): Score {.d
if depth > 1 and self.shouldStop():
return
bestScore = max(score, bestScore)
let nodeType = if score >= beta: LowerBound elif score <= alpha: UpperBound else: Exact
when defined(useTT):
self.transpositionTable.store(depth.uint8, score, self.board.position.zobristKey, nodeType)
if nodeType == LowerBound:
if score >= beta:
# score >= beta
# This move was too good for us, opponent will not search it
break
@ -302,6 +298,10 @@ proc search(self: SearchManager, depth, ply: int, alpha, beta: Score): Score {.d
if ply == 0:
self.bestMoveRoot = move
self.bestRootScore = bestScore
when defined(useTT):
let nodeType = if bestScore >= beta: LowerBound elif bestScore <= alpha: UpperBound else: Exact
self.transpositionTable.store(depth.uint8, bestScore, self.board.position.zobristKey, bestMove, nodeType)
return bestScore

29
Chess/nimfish/nimfishpkg/transpositions.nim
View File

@ -16,6 +16,7 @@
import zobrist
import eval
import moves
import nint128
@ -37,7 +38,10 @@ type
# fit into an int16
score*: int16
hash*: ZobristKey
depth: uint8
depth*: uint8
# The best move that was found at the
# depth this entry was created at. Could
bestMove*: Move
TTable* = ref object
data: seq[TTEntry]
@ -65,18 +69,27 @@ func getIndex(self: TTable, key: ZobristKey): uint64 =
result = (u128(key.uint64) * u128(self.size)).hi
func store*(self: TTable, depth: uint8, score: Score, hash: ZobristKey, flag: TTentryFlag) =
func store*(self: TTable, depth: uint8, score: Score, hash: ZobristKey, bestMove: Move, flag: TTentryFlag) =
## Stores an entry in the transposition table
self.data[self.getIndex(hash)] = TTEntry(flag: flag, score: int16(score), hash: hash, depth: depth)
self.data[self.getIndex(hash)] = TTEntry(flag: flag, score: int16(score), hash: hash, depth: depth, bestMove: bestMove)
proc get*(self: TTable, hash: ZobristKey, depth: uint8): tuple[success: bool, entry: TTEntry] =
## Attempts to get the entry with the given
## zobrist key at the given depth in the table.
## The success parameter is set to false upon detection
## of a hash collision or if the provided depth is greater
## than the one stored in the table: the result should be
## considered invalid unless it's true
## zobrist key and the given depth in the table.
## The success parameter is set to false upon
## detection of a hash collision or other anomaly:
## the result should be considered invalid unless
## it's true
result.entry = self.data[self.getIndex(hash)]
result.success = result.entry.hash == hash and result.entry.depth >= depth
proc get*(self: TTable, hash: ZobristKey): tuple[success: bool, entry: TTEntry] =
## Attempts to get the entry with the given
## zobrist key in the table. The success parameter
## is set to false upon detection of a hash collision
## or other anomaly: the result should be considered
## invalid unless it's true
result.entry = self.data[self.getIndex(hash)]
result.success = result.entry.hash == hash

6
Chess/nimfish/nimfishpkg/tui.nim
View File

@ -68,6 +68,10 @@ proc perft*(board: var Chessboard, ply: int, verbose = false, divide = false, bu
echo "None"
echo "\n", board.pretty()
board.doMove(move)
when defined(debug):
let incHash = board.position.zobristKey
board.position.hash()
doAssert board.position.zobristKey == incHash, &"{board.position.zobristKey} != {incHash} at {move} ({board.positions[^1].toFEN()})"
if ply == 1:
if move.isCapture():
inc(result.captures)
@ -452,7 +456,7 @@ proc commandLoop*: int =
of "zobrist":
echo board.position.zobristKey.uint64
of "rep":
echo "Position is drawn by repetition: ", if board.position.repetitionDraw: "yes" else: "no"
echo "Position is drawn by repetition: ", if board.drawnByRepetition(): "yes" else: "no"
of "eval":
echo &"Eval: {board.evaluate()}"
else:

35
Chess/nimfish/nimfishpkg/uci.nim
View File

@ -15,8 +15,6 @@
## Implementation of a UCI compatible server
import std/strutils
import std/strformat
import std/atomics
import board
@ -29,7 +27,8 @@ type
UCISession = ref object
debug: bool
board: Chessboard
currentSearch: Atomic[SearchManager]
searchManager: SearchManager
searchThread: ref Thread[tuple[session: UCISession, command: UCICommand]]
hashTableSize: uint64
transpositionTable: TTable
@ -297,14 +296,11 @@ proc bestMove(args: tuple[session: UCISession, command: UCICommand]) {.thread.}
{.cast(gcsafe).}:
# Yes yes nim sure this isn't gcsafe. Now stfu and spawn a thread
var session = args.session
when defined(useTT):
if session.transpositionTable.isNil():
if session.debug:
echo &"info string created {session.hashTableSize} MiB TT"
session.transpositionTable = newTranspositionTable(session.hashTableSize * 1024 * 1024)
var command = args.command
var searcher = newSearchManager(session.board.position, session.transpositionTable)
session.currentSearch.store(searcher)
if session.debug:
echo "info string search worker started"
var searcher = newSearchManager(session.board, session.transpositionTable)
session.searchManager = searcher
var
timeRemaining = (if session.board.position.sideToMove == White: command.wtime else: command.btime)
increment = (if session.board.position.sideToMove == White: command.winc else: command.binc)
@ -357,11 +353,22 @@ proc startUCISession* =
of NewGame:
session.board = newDefaultChessboard()
of Go:
var thread = new Thread[tuple[session: UCISession, command: UCICommand]]
createThread(thread[], bestMove, (session, cmd))
GcRef(thread)
when defined(useTT):
if session.transpositionTable.isNil():
if session.debug:
echo &"info string created {session.hashTableSize} MiB TT"
session.transpositionTable = newTranspositionTable(session.hashTableSize * 1024 * 1024)
session.searchThread = new Thread[tuple[session: UCISession, command: UCICommand]]
createThread(session.searchThread[], bestMove, (session, cmd))
if session.debug:
echo "info string search started"
of Stop:
session.currentSearch.load().stop()
# TODO: Figure this out. Might be move semantics
GcRef(session.searchManager)
session.searchManager.stop()
joinThread(session.searchThread[])
if session.debug:
echo "info string search stopped"
of SetOption:
case cmd.name:
of "Hash":

2
Chess/nimfish/nimfishpkg/zobrist.nim
View File

@ -27,7 +27,7 @@ type
func `xor`*(a, b: ZobristKey): ZobristKey = ZobristKey(a.uint64 xor b.uint64)
func `==`*(a, b: ZobristKey): bool = a.uint64 == b.uint64
func `$`*(a: ZobristKey): string = $a.uint64
proc computeZobristKeys: array[781, ZobristKey] =
## Precomputes our zobrist keys