bitboard.py

import numpy as np


# Bitboard Constants
BOARD_SIZE = 8
FULL_MASK = 0xFFFFFFFFFFFFFFFF

def popcount(x):
    """Counts set bits in a 64-bit integer."""
    return bin(x).count('1')

def bit_to_row_col(bit_mask):
    """Converts a single bit mask to (row, col) coordinates."""
    if bit_mask == 0:
        return -1, -1
    # Find the index of the set bit (0-63)
    # Assumes only one bit is set
    idx = bit_mask.bit_length() - 1
    # Edax/Othello usually maps MSB to A1 (0,0) or LSB to H8 (7,7)
    # Let's align with Edax: A1 is usually high bit.
    # Standard: index 63 is A1, index 0 is H8.
    # row = (63 - idx) // 8
    # col = (63 - idx) % 8
    # However, standard bit manipulation often uses LSB=0.
    # Let's check Edax conventions later, but for now standard math:
    row = (63 - idx) // 8
    col = (63 - idx) % 8
    return row, col

def get_bit(row, col):
    """Returns a bitmask with a single bit set at (row, col)."""
    shift = 63 - (row * 8 + col)
    return 1 << shift

def make_input_planes(player_bb, opponent_bb):
    """
    Converts bitboards into a 3x8x8 input tensor for the Neural Network.
    Plane 0: Player pieces (1 if present, 0 otherwise)
    Plane 1: Opponent pieces (1 if present, 0 otherwise)
    Plane 2: Constant 1 (indicating it's the player's turn, or generally providing board usage context)
             Some implementations use 'Valid Moves' here instead.
             Let's use a constant plane for now as per AlphaZero standard, 
             or we can update to valid moves if we have them handy.
    """
    planes = np.zeros((3, 8, 8), dtype=np.float32)
    
    # Fill Plane 0 (Player)
    for r in range(8):
        for c in range(8):
            mask = get_bit(r, c)
            if player_bb & mask:
                planes[0, r, c] = 1.0
                
    # Fill Plane 1 (Opponent)
    for r in range(8):
        for c in range(8):
            mask = get_bit(r, c)
            if opponent_bb & mask:
                planes[1, r, c] = 1.0
    
    # Fill Plane 2 (Constant / Color)
    # Often for single-network (canonical form), this might just be 1s.
    planes[2, :, :] = 1.0
    
    import torch
    return torch.tensor(planes).unsqueeze(0) # Add batch dimension: (1, 3, 8, 8)

def print_board(black_bb, white_bb):
    """Prints the board state using B/W symbols."""
    print("  A B C D E F G H")
    for r in range(8):
        line = f"{r+1} "
        for c in range(8):
            mask = get_bit(r, c)
            if black_bb & mask:
                line += "B "
            elif white_bb & mask:
                line += "W "
            else:
                line += ". "
        print(line)