mirror of
https://github.com/epasveer/seer.git
synced 2026-08-30 00:50:42 +08:00
Ernie Pasveer
127 lines
3.9 KiB
Fortran
127 lines
3.9 KiB
Fortran
! ============================================
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! Module: Search
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! Purpose: AI search algorithm
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! ============================================
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MODULE Search
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USE Chess_Types
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USE Board_Utils
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USE Move_Generation
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USE Make_Unmake
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USE Evaluation
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IMPLICIT NONE
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PRIVATE
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PUBLIC :: find_best_move
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INTEGER, PARAMETER :: MATE_SCORE = 100000 ! A score indicating checkmate
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INTEGER, PARAMETER :: INF = MATE_SCORE + 1000 ! Represents infinity
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CONTAINS
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! --- Negamax Search (Recursive Helper) ---
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RECURSIVE INTEGER FUNCTION negamax(board, depth, alpha, beta) RESULT(best_score)
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TYPE(Board_Type), INTENT(INOUT) :: board ! Needs INOUT for make/unmake
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INTEGER, INTENT(IN) :: depth, alpha, beta
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INTEGER :: score, current_alpha
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TYPE(Move_Type), DIMENSION(MAX_MOVES) :: moves
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INTEGER :: num_moves, i
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TYPE(Move_Type) :: current_move
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TYPE(UnmakeInfo_Type) :: unmake_info
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LOGICAL :: in_check
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current_alpha = alpha ! Local copy to modify
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! 1. Depth check
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IF (depth <= 0) THEN
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best_score = evaluate_board(board)
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RETURN
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END IF
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! 2. Generate moves
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CALL generate_moves(board, moves, num_moves)
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! 3. Checkmate / Stalemate check
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IF (num_moves == 0) THEN
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in_check = is_in_check(board, board%current_player)
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IF (in_check) THEN
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best_score = -MATE_SCORE + (10 - depth) ! Lose faster if deeper mate
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ELSE
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best_score = 0 ! Stalemate
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END IF
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RETURN
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END IF
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! 4. Iterate through moves
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best_score = -INF ! Initialize with worst score
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DO i = 1, num_moves
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current_move = moves(i)
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CALL make_move(board, current_move, unmake_info)
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score = -negamax(board, depth - 1, -beta, -current_alpha) ! Recursive call
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CALL unmake_move(board, current_move, unmake_info)
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! Update best score and alpha
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IF (score > best_score) THEN
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best_score = score
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END IF
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IF (best_score > current_alpha) THEN
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current_alpha = best_score
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END IF
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! Beta cutoff
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IF (current_alpha >= beta) THEN
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EXIT ! Prune remaining moves
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END IF
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END DO
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END FUNCTION negamax
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! --- Find Best Move (Top Level Search Call) ---
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SUBROUTINE find_best_move(board, depth, best_move_found, best_move)
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TYPE(Board_Type), INTENT(INOUT) :: board
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INTEGER, INTENT(IN) :: depth
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LOGICAL, INTENT(OUT) :: best_move_found
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TYPE(Move_Type), INTENT(OUT) :: best_move
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TYPE(Move_Type), DIMENSION(MAX_MOVES) :: moves
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INTEGER :: num_moves, i
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INTEGER :: score, best_score_so_far, alpha, beta
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TYPE(Move_Type) :: current_move
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TYPE(UnmakeInfo_Type) :: unmake_info
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best_move_found = .FALSE.
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best_score_so_far = -INF
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alpha = -INF
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beta = INF
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CALL generate_moves(board, moves, num_moves)
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IF (num_moves == 0) THEN
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RETURN ! No legal moves
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END IF
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best_move = moves(1) ! Default to first move
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best_move_found = .TRUE.
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DO i = 1, num_moves
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current_move = moves(i)
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CALL make_move(board, current_move, unmake_info)
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score = -negamax(board, depth - 1, -beta, -alpha)
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CALL unmake_move(board, current_move, unmake_info)
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IF (score > best_score_so_far) THEN
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best_score_so_far = score
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best_move = current_move
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END IF
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! Update alpha (for root node, mainly tracking best score)
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IF (best_score_so_far > alpha) THEN
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alpha = best_score_so_far
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END IF
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! No beta cutoff at root usually, we want the actual best move
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END DO
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END SUBROUTINE find_best_move
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END MODULE Search
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