ZobristHash.py

# A program to illustrate Zobrist Hashing Algorithm
# Taken from GeeksforGeeks
# at https://www.geeksforgeeks.org/minimax-algorithm-in-game-theory-set-5-zobrist-hashing/amp/


import random

# Generates a Random number from 0 to 2^64-1


def randomInt():

    min = 0

    max = pow(2, 64)

    return random.randint(min, max)


# This function associates each piece with
# a number


def indexOf(piece):

    if piece == "wp":

        return 0

    elif piece == "wN":

        return 1

    elif piece == "wB":

        return 2

    elif piece == "wR":

        return 3

    elif piece == "wQ":

        return 4

    elif piece == "wK":

        return 5

    elif piece == "bp":

        return 6

    elif piece == "bN":

        return 7

    elif piece == "bB":

        return 8

    elif piece == "bR":

        return 9

    elif piece == "bQ":

        return 10

    elif piece == "bK":

        return 11

    else:

        return -1


# Initializes the table


def initTable():

    # 8x8x12 array

    ZobristTable = [
        [[randomInt() for k in range(12)] for j in range(8)] for i in range(8)
    ]

    return ZobristTable


# Computes the hash value of a given board


def initHash(board, ZobristTable):

    h = 0

    for i in range(8):

        for j in range(8):

            if board[i][j] != "--":

                piece = indexOf(board[i][j])

                h ^= ZobristTable[i][j][piece]

    return h


# A function that hashes the current gs given previous hash and current move
def hashMove(move, previous, Zobrist):
    newHash = previous ^ Zobrist[move.startRow][move.startCol][indexOf(move.pieceMoved)]
    newHash = newHash ^ Zobrist[move.endRow][move.endCol][indexOf(move.pieceMoved)]
    if move.pieceCaptured != "--":
        newHash = (
            newHash ^ Zobrist[move.endRow][move.endCol][indexOf(move.pieceCaptured)]
        )

    return newHash