All files / web/src/arcade-games/rithmomachia/utils zobristHash.ts

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
import type { Color, Piece, PieceType } from '../types'

/**
 * Zobrist hashing for efficient board state comparison and repetition detection.
 * Each combination of (piece type, color, square) gets a unique random number.
 * The hash of a position is the XOR of all piece hashes.
 */

// Zobrist hash table: [pieceType][color][square] => hash
type ZobristTable = Record<PieceType, Record<Color, Record<string, bigint>>>

// Single zobrist table instance (initialized lazily)
let zobristTable: ZobristTable | null = null

// Turn hash (XOR this when it's Black's turn)
let turnHash: bigint | null = null

/**
 * Simple seedable PRNG using xorshift128+
 */
class SeededRandom {
  private state0: bigint
  private state1: bigint

  constructor(seed: number) {
    // Initialize state from seed
    this.state0 = BigInt(seed)
    this.state1 = BigInt(seed * 2 + 1)
  }

  next(): bigint {
    let s1 = this.state0
    const s0 = this.state1
    this.state0 = s0
    s1 ^= s1 << 23n
    s1 ^= s1 >> 17n
    s1 ^= s0
    s1 ^= s0 >> 26n
    this.state1 = s1
    return (s0 + s1) & 0xffffffffffffffffn // 64-bit mask
  }
}

/**
 * Initialize the Zobrist hash table with deterministic random values.
 */
function initZobristTable(): ZobristTable {
  const rng = new SeededRandom(0x52495448) // "RITH" as seed

  const table: ZobristTable = {
    C: { W: {}, B: {} },
    T: { W: {}, B: {} },
    S: { W: {}, B: {} },
    P: { W: {}, B: {} },
  }

  const pieceTypes: PieceType[] = ['C', 'T', 'S', 'P']
  const colors: Color[] = ['W', 'B']

  // Generate hash for each (pieceType, color, square) combination
  for (const type of pieceTypes) {
    for (const color of colors) {
      for (let file = 0; file < 16; file++) {
        for (let rank = 1; rank <= 8; rank++) {
          const square = `${String.fromCharCode(65 + file)}${rank}`
          table[type][color][square] = rng.next()
        }
      }
    }
  }

  return table
}

/**
 * Get the Zobrist hash table (lazy initialization).
 */
function getZobristTable(): ZobristTable {
  if (!zobristTable) {
    zobristTable = initZobristTable()
    // Also initialize turn hash
    const rng = new SeededRandom(0x5455524e) // "TURN" as seed
    turnHash = rng.next()
  }
  return zobristTable
}

/**
 * Get the turn hash value.
 */
function getTurnHash(): bigint {
  if (turnHash === null) {
    getZobristTable() // This will also initialize turnHash
  }
  return turnHash!
}

/**
 * Compute the Zobrist hash for a board position.
 */
export function computeZobristHash(pieces: Record<string, Piece>, turn: Color): string {
  const table = getZobristTable()
  let hash = 0n

  // XOR all piece hashes
  for (const piece of Object.values(pieces)) {
    if (piece.captured) continue

    const pieceHash = table[piece.type][piece.color][piece.square]
    if (pieceHash) {
      hash ^= pieceHash
    }
  }

  // XOR turn hash if it's Black's turn
  if (turn === 'B') {
    hash ^= getTurnHash()
  }

  // Return as hex string
  return hash.toString(16).padStart(16, '0')
}

/**
 * Check if a hash appears N times in the history (for repetition detection).
 */
export function countHashOccurrences(hashes: string[], targetHash: string): number {
  return hashes.filter((h) => h === targetHash).length
}

/**
 * Check for threefold repetition (hash appears 3 times).
 */
export function isThreefoldRepetition(hashes: string[]): boolean {
  if (hashes.length < 3) return false

  const currentHash = hashes[hashes.length - 1]
  return countHashOccurrences(hashes, currentHash) >= 3
}

/**
 * Incrementally update a Zobrist hash after a move.
 * This is more efficient than recomputing from scratch.
 */
export function updateZobristHash(
  currentHash: string,
  movedPiece: Piece,
  fromSquare: string,
  toSquare: string,
  capturedPiece: Piece | null,
  newTurn: Color
): string {
  const table = getZobristTable()
  let hash = BigInt(`0x${currentHash}`)

  // Remove moved piece from old square
  const oldPieceHash = table[movedPiece.type][movedPiece.color][fromSquare]
  if (oldPieceHash) {
    hash ^= oldPieceHash
  }

  // Add moved piece to new square
  const newPieceHash = table[movedPiece.type][movedPiece.color][toSquare]
  if (newPieceHash) {
    hash ^= newPieceHash
  }

  // Remove captured piece (if any)
  if (capturedPiece) {
    const capturedHash = table[capturedPiece.type][capturedPiece.color][capturedPiece.square]
    if (capturedHash) {
      hash ^= capturedHash
    }
  }

  // Toggle turn (XOR turn hash twice = no change, once = change)
  hash ^= getTurnHash()

  return hash.toString(16).padStart(16, '0')
}