checksmix 0.2.2

A simplified MIX simulator - Donald Knuth's hypothetical computer for teaching and learning assembly language programming.
Documentation 
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        % ----------------------------------------------------
        % Data segment: statically allocate three nodes
        % ----------------------------------------------------
        LOC     Data_Segment
        GREG    @
Node1   OCTA    1               % node1.value = 1
        OCTA    Node2           % node1.next = Node2
Node2   OCTA    2               % node2.value = 2
        OCTA    Node3           % node2.next = Node3
Node3   OCTA    3               % node3.value = 3
        OCTA    0               % node3.next = NULL

        % ----------------------------------------------------
        % Program segment
        % ----------------------------------------------------
        LOC     #100

        % ----------------------------------------------------
        % Registers used:
        %   $0 = 0
        %   $1 = head pointer
        %   $2 = current value
        %   $4 = temp
        %   $5 = sum
        % ----------------------------------------------------

Start   SET     $0,0                % constant zero register initialization
        SET     $5,0                % sum = 0
        LDA     $1,Node1            % head = address of node1

        % -------- traversal: sum all values --------
Traverse
        CMP     $4,$1,$0            % compare head to NULL
        BZ      $4,Done             % if equal (zero result), exit

        LDO     $2,$1,$0            % load value from node
        ADD     $5,$5,$2            % sum += value

        LDOI    $1,$1,8             % move to next node (load from offset 8)
        JMP     Traverse

Done
        % Return sum in $5, exit gracefully
        SET     $255,0              % status code 0
        TRAP    0,0,0