Discussion on: Advent of Code 2020 Solution Megathread - Day 8: Handheld Halting

   IDENTIFICATION DIVISION.
   PROGRAM-ID. AOC-2020-08-1.
   AUTHOR ANNA KOSIERADZKA.

   ENVIRONMENT DIVISION.
   INPUT-OUTPUT SECTION.
   FILE-CONTROL.
       SELECT INPUTFILE ASSIGN TO "d08.input"
       ORGANIZATION IS LINE SEQUENTIAL.

   DATA DIVISION.
   FILE SECTION.
     FD INPUTFILE.
     01 INPUTRECORD. 
       05 INPUT-INSTRUCTION PIC X(3).
       05 INPUT-SPACE PIC X.
       05 INPUT-SIGN PIC X(1).
       05 INPUT-ARG PIC 9(3).

   WORKING-STORAGE SECTION.
     01 FILE-STATUS PIC 9 VALUE 0.
     01 WS-CODE OCCURS 625 TIMES.
       05 WS-INSTRUCTION PIC X(3).
       05 WS-SIGN PIC X.
       05 WS-ARG PIC 9(3).
       05 WS-DONE PIC 9 VALUE 0.
     01 WS-I PIC X(3).
     01 WS-ACC PIC S9(6) VALUE 0.

   LOCAL-STORAGE SECTION.
     01 I UNSIGNED-INT VALUE 1.
     01 ARG UNSIGNED-INT VALUE 0.
     01 CODE-POS UNSIGNED-INT VALUE 1.

   PROCEDURE DIVISION.
   001-MAIN.
       OPEN INPUT INPUTFILE.
       PERFORM 002-READ UNTIL FILE-STATUS = 1.
       CLOSE INPUTFILE.
       PERFORM 004-RUN-CODE.
       DISPLAY WS-ACC.
       STOP RUN.

   002-READ.
        READ INPUTFILE
            AT END MOVE 1 TO FILE-STATUS
            NOT AT END PERFORM 003-PROCESS-RECORD
        END-READ.

   003-PROCESS-RECORD.
       MOVE INPUT-INSTRUCTION TO WS-INSTRUCTION(I).
       MOVE INPUT-SIGN TO WS-SIGN(I).
       MOVE INPUT-ARG TO WS-ARG(I).
       ADD 1 TO I.

   004-RUN-CODE.
       PERFORM 005-RUN-INSTRUCTION UNTIL WS-DONE(CODE-POS) = 1.

   005-RUN-INSTRUCTION.
       MOVE 1 TO WS-DONE(CODE-POS).
       MOVE WS-INSTRUCTION(CODE-POS) TO WS-I.
       COMPUTE ARG = FUNCTION NUMVAL(WS-ARG(CODE-POS)).

       IF WS-I = "nop" THEN 
          ADD 1 TO CODE-POS
       END-IF.

       IF WS-I = "acc" THEN 
          IF WS-SIGN(CODE-POS) = "+" THEN
            COMPUTE WS-ACC = WS-ACC + ARG
          ELSE 
            COMPUTE WS-ACC = WS-ACC - ARG
          END-IF
          ADD 1 TO CODE-POS
       END-IF.

       IF WS-I = "jmp" THEN 
          IF WS-SIGN(CODE-POS) = "+" THEN
            COMPUTE CODE-POS = CODE-POS + ARG
          ELSE 
            COMPUTE CODE-POS = CODE-POS - ARG
          END-IF
       END-IF.