COBOL による Fibonacci 数の計算

fibonacci.cob

IDENTIFICATION DIVISION.
    PROGRAM-ID. FIBONACCI.

DATA DIVISION.
    WORKING-STORAGE SECTION.
        01 ARGUMENT PIC 9(2).
        01 RETURN-VALUE PIC 9(25).
        01 RESULT PIC Z(25).
        01 DP-TABLE.
            03 VALS PIC 9(25) OCCURS 99.
        01 TABLE-INDEX PIC 9(2).
        01 AUX-INDEX-1 PIC 9(2).
        01 AUX-INDEX-2 PIC 9(2).

PROCEDURE DIVISION.
    
    *> 主処理
    MAIN SECTION.
        
        DISPLAY "Index: "
        ACCEPT ARGUMENT.
        PERFORM FIBONACCI.
        
        MOVE RETURN-VALUE TO RESULT.
        DISPLAY "Result: " RESULT.
        
        STOP RUN.
        
    *> ARGUMENT の Fibonacci 数を計算し RETURN-VALUE に格納
    FIBONACCI SECTION.
        
        MOVE 1 TO TABLE-INDEX.
        PERFORM UNTIL TABLE-INDEX > ARGUMENT
            
            MOVE 0 TO VALS(TABLE-INDEX)
            EVALUATE TABLE-INDEX
                WHEN 1
                WHEN 2
                    MOVE 1 TO VALS(TABLE-INDEX)
                WHEN OTHER
                    SUBTRACT 1 FROM TABLE-INDEX GIVING AUX-INDEX-1
                    SUBTRACT 2 FROM TABLE-INDEX GIVING AUX-INDEX-2
                    ADD VALS(AUX-INDEX-1) TO VALS(TABLE-INDEX)
                    ADD VALS(AUX-INDEX-2) TO VALS(TABLE-INDEX)
            END-EVALUATE
            
            ADD 1 TO TABLE-INDEX
        END-PERFORM.
        
        MOVE VALS(ARGUMENT) TO RETURN-VALUE.