Execute Computer/Zero

From Rosetta Code
Task
Execute Computer/Zero
You are encouraged to solve this task according to the task description, using any language you may know.
Execute Computer/Zero is an implementation of Computer/zero Assembly. Other implementations of Computer/zero Assembly.
Task

Create a Computer/zero Assembly emulator. You may consider this webpage as a reference implementation. Output the results of the sample programs "2+2" and "7*8" found there.

  •   The virtual machine "bytecode" needs to be able to modify itself (or at least act as though it can) while the virtual machine is running, to be consistent with the reference implementation.
  •   For output, it is sufficient to have the implementation of the STP opcode return the accumulator to your actual language, and then use your standard printing routines to output it.
Bonus Points
Run all 5 sample programs at the aforementioned website and output their results.




ALGOL 68[edit]

BEGIN # execute some ComputerZero programs                                 #
    # instructions                                                         #
    INT nop = 0, lda = 1, sta = 2, add = 3, sub = 4, brz = 5, jmp = 6, stp = 7;
    PROC instr   = ( INT op, v )INT: ( 32 * op ) + v;
    OP NOP       = ( INT v     )INT: instr( nop, v );
    OP LDA       = ( INT v     )INT: instr( lda, v );
    OP STA       = ( INT v     )INT: instr( sta, v );
    OP ADD       = ( INT v     )INT: instr( add, v );
    OP SUB       = ( INT v     )INT: instr( sub, v );
    OP BRZ       = ( INT v     )INT: instr( brz, v );
    OP JMP       = ( INT v     )INT: instr( jmp, v );
    OP STP       = ( INT v     )INT: instr( stp, v );
    # executes the program named name                                      #
    PROC execute = ( STRING name, []INT program )VOID:
         BEGIN
            [ 0 : 31 ]INT m; # the computer 32 has bytes of memory         #
            FOR i FROM LWB m TO UPB m DO m[ i ] := 0 OD;
            # "assemble" the program                                       #
            INT m pos := -1;
            FOR i FROM LWB program TO UPB program DO
                m[ m pos +:= 1 ] := program[ i ]
            OD;
            # execute the program #
            BOOL running := TRUE;
            INT  pc      := 0;
            INT  a       := 0;
            WHILE running DO
                INT op      := m[ pc ] OVER 32;
                INT operand := m[ pc ] MOD  32;
                pc +:= 1 MODAB 32;
                IF   op = nop THEN SKIP
                ELIF op = lda THEN a  := m[ operand ]
                ELIF op = sta THEN m[ operand ] := a
                ELIF op = add THEN a +:= m[ operand ] MODAB 256
                ELIF op = sub THEN a -:= m[ operand ] MODAB 256
                ELIF op = brz THEN IF a = 0 THEN pc := operand FI
                ELIF op = jmp THEN pc := operand
                ELSE #    stp #
                    running := FALSE;
                    print( ( " " * ( 12 - ( ( UPB name - LWB name ) + 1 ) ) ) );
                    print( ( name, ": ", whole( a, -3 ), newline ) )
                FI
            OD
         END # execute # ;
    # task test programs (from the Computer Zero website)                  #
    # the unary NOP, LDA, STA, etc. operators are used to construct the    #
    # instructions; as parameterless operators aren't allowed, NOP and STP #
    # must have a dummy parameter                                          #
    execute( "2+2",  ( LDA  3, ADD  4, STP  0,      2,      2 )
           );
    execute( "7*8"
           , ( LDA 12, ADD 10, STA 12, LDA 11, SUB 13, STA 11, BRZ  8, JMP  0
             , LDA 12, STP  0,      8,      7,      0,      1
             )
           );
    execute( "fibonacci"
           , ( LDA 14, STA 15, ADD 13, STA 14, LDA 15, STA 13, LDA 16, SUB 17
             , BRZ 11, STA 16, JMP  0, LDA 14, STP  0,      1,      1,      0
             ,      8,      1
             )
           );
    execute( "linkedList"
           , ( LDA 13, ADD 15, STA  5, ADD 16, STA  7, NOP  0, STA 14, NOP  0
             , BRZ 11, STA 15, JMP  0, LDA 14, STP  0, LDA  0,      0,     28
             ,      1,      0,      0,      0,      6,      0,      2,     26
             ,      5,     20,      3,     30,      1,     22,      4,     24
             )
           );
    execute( "prisoner"
           , ( NOP  0, NOP  0, STP  0,      0, LDA  3, SUB 29, BRZ 18, LDA  3
             , STA 29, BRZ 14, LDA  1, ADD 31, STA  1, JMP  2, LDA  0, ADD 31
             , STA  0, JMP  2, LDA  3, STA 29, LDA  1, ADD 30, ADD  3, STA  1
             , LDA  0, ADD 30, ADD  3, STA  0, JMP  2,      0,      1,      3
             )
           );
    # subtractions yielding negative results                               #
    execute( "0-255", ( LDA  3, SUB  4, STP  0,      0,    255 ) );
    execute( "0-1",   ( LDA  3, SUB  4, STP  0,      0,      1 ) );
    # overflow on addition                                                 #
    execute( "1+255", ( LDA  3, ADD  4, STP  0,      1,    255 ) )
END
Output:
         2+2:   4
         7*8:  56
   fibonacci:  55
  linkedList:   6
    prisoner:   0
       0-255:   1
         0-1: 255
       1+255:   0

Applesoft BASIC[edit]

 0  FOR P = 1 TO 5: READ S$: PRINT S$" : ";: FOR MEM = 0 TO 31: ON  LEN (S$) > 0 GOSUB 90:A =  VAL (S$): GOSUB 2: NEXT MEM: GOSUB 7: PRINT A: NEXT P: END 
 1  LET A = V: RETURN 
 2  LET P$ =  MID$ (P$,1,MEM) +  CHR$ (A) +  MID$ (P$,MEM + 2,31 - MEM): PRINT  MID$ ("",1 ^  FRE (0));: RETURN 
 3  LET A = A + V:A = A - 256 * (A > 255): RETURN 
 4  LET A = A - V:A = A + 256 * (A < 0): RETURN 
 5  IF A > 0 THEN  RETURN 
 6  LET PC = MEM: RETURN 
 7  LET PC = 0
 8  LET A = 0
 9  FOR OP = 0 TO 7 STEP 0
 10     LET PC = PC + 1 - 32 * (PC = 32)
 20     LET I =  ASC ( MID$ (P$,PC,1))
 30     LET OP =  INT (I / 32)
 40     LET MEM = I - OP * 32
 50     LET V =  ASC ( MID$ (P$,MEM + 1,1))
 60     ON OP GOSUB 1,2,3,4,5,6
 70  NEXT OP
 80  RETURN 
 90  READ S$: RETURN 
 100  DATA "2+2",35,100,224,2,2,
 200  DATA "7*8",44,106,76,43,141,75,168,192,44,224,8,7,0,1,
 300  DATA "FIBONACCI",46,79,109,78,47,77,48,145,171,80,192,46,224,1,1,0,8,1,
 400  DATA "LINKED LIST",45,111,69,112,71,0,78,0,171,79,192,46,224,32,0,28,1,0,0,0,6,0,2,26,5,20,3,30,1,22,4,24
 500  DATA "PRISONER",0,0,224,0,0,35,157,178,35,93,174,33,127,65,194,32,127,64,192,35,93,33,126,99,

Forth[edit]

Works with: gforth version 0.7.3


#! /usr/bin/gforth

\ Execute Computer/Zero

\ reserve 32 cells for memory

CREATE MEMORY 32 cells allot
MEMORY 32 cells erase


\ gets the address of the memory cell with the given index
: mem ( ix - addr )
    cells MEMORY +
;

\ splits a byte into instruction and argument
: instruction ( ix -> arg inst )
    mem @ dup
    32 mod swap
    32 /
;

\ defines a program by giving its name and the 32 memory contents (in binary)
: PROGRAM ( "name" "b01" ... "b31" -- )
    CREATE
        base @ >r 2 base !
        32 0 DO
            BEGIN
                parse-name
            dup 0= WHILE
                2drop refill drop
            REPEAT
            s>number? 2drop ,
        LOOP
        r> base !
    DOES> ( -- n00 ... n31 )
        32 0 DO
            dup @ swap cell+
        LOOP
        drop
;

\ loads 32 bytes from the stack into memory
: >memory ( n00 ... n31 -- )
    -1 31 -DO
        i mem !
    1 -LOOP
;

\ prints accumulator and program counter
: .acc-pc ( acc pc -- acc pc )
    over 3 .r dup 3 .r
;

\ prints the argument
: .x ( x -- x )
    dup 2 .r
;

\ performs one step of the simulation
: step ( acc pc -- acc' pc' )
    .acc-pc ."  : "
    tuck instruction CASE
        0 OF ." NOP " .x drop                          swap 1+      ENDOF
        1 OF ." LDA " .x nip mem @                     swap 1+      ENDOF
        2 OF ." STA " .x over swap mem !               swap 1+      ENDOF
        3 OF ." ADD " .x mem @ + 256 mod               swap 1+      ENDOF
        4 OF ." SUB " .x mem @ - 256 mod               swap 1+      ENDOF
        5 OF ." BRZ " .x over 0= if rot drop else drop swap 1+ then ENDOF
        6 OF ." JMP " .x            rot drop                        ENDOF
        7 OF ." STP " .x drop nip -1                                ENDOF
    ENDCASE
    ."  -> " .acc-pc
;

\ runs the simulation, starting with accumulator zero and program counter zero
: run ( -- acc )
    0 0 cr
    BEGIN
    dup 0>= WHILE
        step cr
    REPEAT
    drop
;


\ the five example programs

PROGRAM 2+2
    00100011 01100100
    11100000 00000010
    00000010 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000

PROGRAM 7*8
    00101100 01101010
    01001100 00101011
    10001101 01001011
    10101000 11000000
    00101100 11100000
    00001000 00000111
    00000000 00000001
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000

PROGRAM Fibonacci
    00101110 01001111
    01101101 01001110
    00101111 01001101
    00110000 10010001
    10101011 01010000
    11000000 00101110
    11100000 00000001
    00000001 00000000
    00001000 00000001
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000
    00000000 00000000

PROGRAM List'
    00101101 01101111
    01000101 01110000
    01000111 00000000
    01001110 00000000
    10101011 01001111
    11000000 00101110
    11100000 00100000
    00000000 00011100
    00000001 00000000
    00000000 00000000
    00000110 00000000
    00000010 00011010
    00000101 00010100
    00000011 00011110
    00000001 00010110
    00000100 00011000

PROGRAM Prisoner
    00000000 00000000
    11100000 00000000
    00100011 10011101
    10110010 00100011
    01011101 10101110
    00100001 01111111
    01000001 11000010
    00100000 01111111
    01000000 11000010
    00100011 01011101
    00100001 01111110
    01100011 01000001
    00100000 01111110
    01100011 01000000
    11000010 00000000
    00000001 00000011


\ runs a program and drops the result
: run-sample-program ( -- )
    >memory run drop
;


\ run the five example programs

2+2       run-sample-program
7*8       run-sample-program
Fibonacci run-sample-program
List'     run-sample-program
Prisoner  run-sample-program

bye
Output:
 0  0 : LDA  3 ->   2  1
 2  1 : ADD  4 ->   4  2
 4  2 : STP  0 ->   4 -1
 0  0 : LDA 12 ->   0  1
 0  1 : ADD 10 ->   8  2
 8  2 : STA 12 ->   8  3
 8  3 : LDA 11 ->   7  4
 7  4 : SUB 13 ->   6  5
 6  5 : STA 11 ->   6  6
 6  6 : BRZ  8 ->   6  7
 6  7 : JMP  0 ->   6  0
 6  0 : LDA 12 ->   8  1
 8  1 : ADD 10 ->  16  2
16  2 : STA 12 ->  16  3
16  3 : LDA 11 ->   6  4
 6  4 : SUB 13 ->   5  5
 5  5 : STA 11 ->   5  6
 5  6 : BRZ  8 ->   5  7
 5  7 : JMP  0 ->   5  0
 5  0 : LDA 12 ->  16  1
16  1 : ADD 10 ->  24  2
24  2 : STA 12 ->  24  3
24  3 : LDA 11 ->   5  4
 5  4 : SUB 13 ->   4  5
 4  5 : STA 11 ->   4  6
 4  6 : BRZ  8 ->   4  7
 4  7 : JMP  0 ->   4  0
 4  0 : LDA 12 ->  24  1
24  1 : ADD 10 ->  32  2
32  2 : STA 12 ->  32  3
32  3 : LDA 11 ->   4  4
 4  4 : SUB 13 ->   3  5
 3  5 : STA 11 ->   3  6
 3  6 : BRZ  8 ->   3  7
 3  7 : JMP  0 ->   3  0
 3  0 : LDA 12 ->  32  1
32  1 : ADD 10 ->  40  2
40  2 : STA 12 ->  40  3
40  3 : LDA 11 ->   3  4
 3  4 : SUB 13 ->   2  5
 2  5 : STA 11 ->   2  6
 2  6 : BRZ  8 ->   2  7
 2  7 : JMP  0 ->   2  0
 2  0 : LDA 12 ->  40  1
40  1 : ADD 10 ->  48  2
48  2 : STA 12 ->  48  3
48  3 : LDA 11 ->   2  4
 2  4 : SUB 13 ->   1  5
 1  5 : STA 11 ->   1  6
 1  6 : BRZ  8 ->   1  7
 1  7 : JMP  0 ->   1  0
 1  0 : LDA 12 ->  48  1
48  1 : ADD 10 ->  56  2
56  2 : STA 12 ->  56  3
56  3 : LDA 11 ->   1  4
 1  4 : SUB 13 ->   0  5
 0  5 : STA 11 ->   0  6
 0  6 : BRZ  8 ->   0  8
 0  8 : LDA 12 ->  56  9
56  9 : STP  0 ->  56 -1
 0  0 : LDA 14 ->   1  1
 1  1 : STA 15 ->   1  2
 1  2 : ADD 13 ->   2  3
 2  3 : STA 14 ->   2  4
 2  4 : LDA 15 ->   1  5
 1  5 : STA 13 ->   1  6
 1  6 : LDA 16 ->   8  7
 8  7 : SUB 17 ->   7  8
 7  8 : BRZ 11 ->   7  9
 7  9 : STA 16 ->   7 10
 7 10 : JMP  0 ->   7  0
 7  0 : LDA 14 ->   2  1
 2  1 : STA 15 ->   2  2
 2  2 : ADD 13 ->   3  3
 3  3 : STA 14 ->   3  4
 3  4 : LDA 15 ->   2  5
 2  5 : STA 13 ->   2  6
 2  6 : LDA 16 ->   7  7
 7  7 : SUB 17 ->   6  8
 6  8 : BRZ 11 ->   6  9
 6  9 : STA 16 ->   6 10
 6 10 : JMP  0 ->   6  0
 6  0 : LDA 14 ->   3  1
 3  1 : STA 15 ->   3  2
 3  2 : ADD 13 ->   5  3
 5  3 : STA 14 ->   5  4
 5  4 : LDA 15 ->   3  5
 3  5 : STA 13 ->   3  6
 3  6 : LDA 16 ->   6  7
 6  7 : SUB 17 ->   5  8
 5  8 : BRZ 11 ->   5  9
 5  9 : STA 16 ->   5 10
 5 10 : JMP  0 ->   5  0
 5  0 : LDA 14 ->   5  1
 5  1 : STA 15 ->   5  2
 5  2 : ADD 13 ->   8  3
 8  3 : STA 14 ->   8  4
 8  4 : LDA 15 ->   5  5
 5  5 : STA 13 ->   5  6
 5  6 : LDA 16 ->   5  7
 5  7 : SUB 17 ->   4  8
 4  8 : BRZ 11 ->   4  9
 4  9 : STA 16 ->   4 10
 4 10 : JMP  0 ->   4  0
 4  0 : LDA 14 ->   8  1
 8  1 : STA 15 ->   8  2
 8  2 : ADD 13 ->  13  3
13  3 : STA 14 ->  13  4
13  4 : LDA 15 ->   8  5
 8  5 : STA 13 ->   8  6
 8  6 : LDA 16 ->   4  7
 4  7 : SUB 17 ->   3  8
 3  8 : BRZ 11 ->   3  9
 3  9 : STA 16 ->   3 10
 3 10 : JMP  0 ->   3  0
 3  0 : LDA 14 ->  13  1
13  1 : STA 15 ->  13  2
13  2 : ADD 13 ->  21  3
21  3 : STA 14 ->  21  4
21  4 : LDA 15 ->  13  5
13  5 : STA 13 ->  13  6
13  6 : LDA 16 ->   3  7
 3  7 : SUB 17 ->   2  8
 2  8 : BRZ 11 ->   2  9
 2  9 : STA 16 ->   2 10
 2 10 : JMP  0 ->   2  0
 2  0 : LDA 14 ->  21  1
21  1 : STA 15 ->  21  2
21  2 : ADD 13 ->  34  3
34  3 : STA 14 ->  34  4
34  4 : LDA 15 ->  21  5
21  5 : STA 13 ->  21  6
21  6 : LDA 16 ->   2  7
 2  7 : SUB 17 ->   1  8
 1  8 : BRZ 11 ->   1  9
 1  9 : STA 16 ->   1 10
 1 10 : JMP  0 ->   1  0
 1  0 : LDA 14 ->  34  1
34  1 : STA 15 ->  34  2
34  2 : ADD 13 ->  55  3
55  3 : STA 14 ->  55  4
55  4 : LDA 15 ->  34  5
34  5 : STA 13 ->  34  6
34  6 : LDA 16 ->   1  7
 1  7 : SUB 17 ->   0  8
 0  8 : BRZ 11 ->   0 11
 0 11 : LDA 14 ->  55 12
55 12 : STP  0 ->  55 -1
 0  0 : LDA 13 ->  32  1
32  1 : ADD 15 ->  60  2
60  2 : STA  5 ->  60  3
60  3 : ADD 16 ->  61  4
61  4 : STA  7 ->  61  5
61  5 : LDA 28 ->   1  6
 1  6 : STA 14 ->   1  7
 1  7 : LDA 29 ->  22  8
22  8 : BRZ 11 ->  22  9
22  9 : STA 15 ->  22 10
22 10 : JMP  0 ->  22  0
22  0 : LDA 13 ->  32  1
32  1 : ADD 15 ->  54  2
54  2 : STA  5 ->  54  3
54  3 : ADD 16 ->  55  4
55  4 : STA  7 ->  55  5
55  5 : LDA 22 ->   2  6
 2  6 : STA 14 ->   2  7
 2  7 : LDA 23 ->  26  8
26  8 : BRZ 11 ->  26  9
26  9 : STA 15 ->  26 10
26 10 : JMP  0 ->  26  0
26  0 : LDA 13 ->  32  1
32  1 : ADD 15 ->  58  2
58  2 : STA  5 ->  58  3
58  3 : ADD 16 ->  59  4
59  4 : STA  7 ->  59  5
59  5 : LDA 26 ->   3  6
 3  6 : STA 14 ->   3  7
 3  7 : LDA 27 ->  30  8
30  8 : BRZ 11 ->  30  9
30  9 : STA 15 ->  30 10
30 10 : JMP  0 ->  30  0
30  0 : LDA 13 ->  32  1
32  1 : ADD 15 ->  62  2
62  2 : STA  5 ->  62  3
62  3 : ADD 16 ->  63  4
63  4 : STA  7 ->  63  5
63  5 : LDA 30 ->   4  6
 4  6 : STA 14 ->   4  7
 4  7 : LDA 31 ->  24  8
24  8 : BRZ 11 ->  24  9
24  9 : STA 15 ->  24 10
24 10 : JMP  0 ->  24  0
24  0 : LDA 13 ->  32  1
32  1 : ADD 15 ->  56  2
56  2 : STA  5 ->  56  3
56  3 : ADD 16 ->  57  4
57  4 : STA  7 ->  57  5
57  5 : LDA 24 ->   5  6
 5  6 : STA 14 ->   5  7
 5  7 : LDA 25 ->  20  8
20  8 : BRZ 11 ->  20  9
20  9 : STA 15 ->  20 10
20 10 : JMP  0 ->  20  0
20  0 : LDA 13 ->  32  1
32  1 : ADD 15 ->  52  2
52  2 : STA  5 ->  52  3
52  3 : ADD 16 ->  53  4
53  4 : STA  7 ->  53  5
53  5 : LDA 20 ->   6  6
 6  6 : STA 14 ->   6  7
 6  7 : LDA 21 ->   0  8
 0  8 : BRZ 11 ->   0 11
 0 11 : LDA 14 ->   6 12
 6 12 : STP  0 ->   6 -1
 0  0 : NOP  0 ->   0  1
 0  1 : NOP  0 ->   0  2
 0  2 : STP  0 ->   0 -1

J[edit]

The reference programs are not supplied in source code form, so in its current form this task is a bit unclear.

Here's one approach which might be sufficiently close to the task requirements:

OPS=: 'nop lda sta add sub brz jmp stp'

assemble1=: {{
  y=. tolower y
  ins=. {.;:y-.":i.10
  cod=. 8|(;:OPS) i. ins
  val=. {.0".y-.OPS
  if. *cod do. 
    assert. 32>val
    val+32*cod
  else.
    assert. 256>val
    val
  end.
}}

assemble=: {{
  if. 0=L. y do.
    delim=. {.((tolower y)-.(":i.10),;OPS),LF
    y=. delim cut y
  end.
  code=. assemble1@> y
  mem=: code (i.#code)} 32#0
}}

exec1=: {{
  'cod val'=. 0 32#:pc{mem
  pc=: 32|pc+1
  select. cod
    case. 0 do.
    case. 1 do. acc=: val{mem
    case. 2 do. mem=: acc val} mem
    case. 3 do. acc=: 256|acc+val{mem
    case. 4 do. acc=: 256|acc-val{mem
    case. 5 do. pc=: 32|pc[^:(*acc) val
    case. 6 do. pc=: 32|val
    case. 7 do. pc=: __
  end.
}}

exec=: {{
  pc=: acc=: 0
  while. 0<:pc do. exec1'' end.
  acc
}}

With this implementation, we can assemble and run representations of the five suggested programs:

   exec assemble 'LDA 3; ADD 4; STP; 2; 2'
4
   exec assemble 'LDA 12; ADD 10; STA 12; LDA 11; SUB 13; STA 11; BRZ 8; JMP; LDA 12; STP; 8; 7; 0; 1'
56
   exec assemble 'LDA 14; STA 15; ADD 13; STA 14; LDA 15; STA 13; LDA 16; SUB 17; BRZ 11; STA 16; JMP; LDA 14; STP; 1; 1; 0; 8; 1'
55
   exec assemble 'LDA 13; ADD 15; STA 5; ADD 16; STA 7; NOP; STA 14; NOP; BRZ 11; STA 15; JMP; LDA 14; STP; LDA; 0; 28; 1; 0; 0; 0; 6; 0; 2; 26; 5; 20; 3; 30; 1; 22; 4; 24'
6
   exec assemble 'NOP; NOP; STP; NOP; LDA 3; SUB 29; BRZ 18; LDA 3; STA 29; BRZ 14; LDA 1; ADD 31; STA 1; JMP 2; LDA; ADD 31; STA; JMP 2; LDA 3; STA 29; LDA 1; ADD 30; ADD 3; STA 1; LDA; ADD 30; ADD 3; STA; JMP 2; 0; 1; 3'
0

Alternate approach[edit]

Another approach would be to eliminate the 'assemble' command and implement the opcodes as native J commands (which build a representation of the memory space). To conform with J syntax, the right arguments of these opcodes is required (so you need a 0 even for NOP and STP). The implementation of exec remains much the same as before, but it's convenient to have exec save the code to memory. In other words:

opcode=: {{
  (m+{.y),}.y
:
  x,m opcode y
}}

({{((x)=: y opcode)0}}&>32*i.@#);:'NOP LDA STA ADD SUB BRZ JMP STP'

exec1=: {{
  'cod val'=. 0 32#:pc{mem
  pc=: 32|pc+1
  select. cod
    case. 0 do.                         NB. NOP
    case. 1 do. acc=: val{mem           NB. LDA
    case. 2 do. mem=: acc val} mem      NB. STA
    case. 3 do. acc=: 256|acc+val{mem   NB. ADD
    case. 4 do. acc=: 256|acc-val{mem   NB. SUB
    case. 5 do. pc=: 32|pc[^:(*acc) val NB. BRZ
    case. 6 do. pc=: 32|val             NB. JMP
    case. 7 do. pc=: __                 NB. STP
  end.
}}

exec=: {{
  mem=: 32{.y
  pc=: acc=: 0
  while. 0<:pc do. exec1'' end.
  acc
}}

and:

   exec LDA 3 ADD 4 STP 0 2 2
4
   exec LDA 12 ADD 10 STA 12 LDA 11 SUB 13 STA 11 BRZ 8 JMP 0 LDA 12 STP 0 8 7 0 1
56
   exec LDA 14 STA 15 ADD 13 STA 14 LDA 15 STA 13 LDA 16 SUB 17 BRZ 11 STA 16 JMP 0 LDA 14 STP 0 1 1 0 8 1
55
   exec LDA 13 ADD 15 STA 5 ADD 16 STA 7 NOP 0 STA 14 NOP 0 BRZ 11 STA 15 JMP 0 LDA 14 STP 0 LDA 0 0 28 1 0 0 0 6 0 2 26 5 20 3 30 1 22 4 24
6
   exec NOP 0 NOP 0 STP 0 NOP 0 LDA 3 SUB 29 BRZ 18 LDA 3 STA 29 BRZ 14 LDA 1 ADD 31 STA 1 JMP 2 LDA 0 ADD 31 STA 0 JMP 2 LDA 3 STA 29 LDA 1 ADD 30 ADD 3 STA 1 LDA 0 ADD 30 ADD 3 STA 0 JMP 2 0 1 3
0

Java[edit]

Translation of: Python
Works with: Java version 8
import static java.lang.Math.floorMod;
import static java.lang.Math.min;
import static java.util.stream.Collectors.toMap;

import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Stream;

public class ComputerZero {

    private static final int MEM = 32;

    private static final int NOP = 0;
    private static final int LDA = 1;
    private static final int STA = 2;
    private static final int ADD = 3;
    private static final int SUB = 4;
    private static final int BRZ = 5;
    private static final int JMP = 6;
    private static final int STP = 7;

    private static final Map<String, Integer> OPCODES = Stream.of(
            new SimpleEntry<>("NOP", NOP),
            new SimpleEntry<>("LDA", LDA),
            new SimpleEntry<>("STA", STA),
            new SimpleEntry<>("ADD", ADD),
            new SimpleEntry<>("SUB", SUB),
            new SimpleEntry<>("BRZ", BRZ),
            new SimpleEntry<>("JMP", JMP),
            new SimpleEntry<>("STP", STP))
            .collect(toMap(SimpleEntry::getKey, SimpleEntry::getValue));

    private static final Pattern RE_INSTRUCTION = Pattern.compile(
            "\\s*" +
                    "(?:(?<label>\\w+):)?" +
                    "\\s*" +
                    String.format("(?<opcode>%s)?", String.join("|", OPCODES.keySet())) +
                    "\\s*" +
                    "(?<argument>\\w+)?" +
                    "\\s*" +
                    "(?:;(?<comment>.+))?");

    public static class ComputerZeroException extends RuntimeException {
        public ComputerZeroException(String msg) {
            super(msg);
        }
    }

    private static class Instruction {
        String opcode;
        String argument;

        public Instruction(String opcode, String argument) {
            this.opcode = opcode;
            this.argument = argument;
        }
    }

    private static class Assembly {
        public Iterable<Instruction> instructions;
        public Map<String, Integer> labels;

        public Assembly(Iterable<Instruction> instructions, Map<String, Integer> labels) {
            this.instructions = instructions;
            this.labels = labels;
        }
    }

    public static Assembly parse(String assembly) {
        ArrayList<Instruction> instructions = new ArrayList<Instruction>();
        HashMap<String, Integer> labels = new HashMap<String, Integer>();
        int lineNumber = 0;

        for (String line : assembly.split("\\R")) {
            Matcher matcher = RE_INSTRUCTION.matcher(line);

            if (!matcher.matches()) {
                throw new ComputerZeroException(String.format("%s %d", line, lineNumber));
            }

            if (matcher.group("label") != null) {
                labels.put(matcher.group("label"), lineNumber);
            }

            instructions.add(new Instruction(matcher.group("opcode"), matcher.group("argument")));
            lineNumber++;
        }

        return new Assembly(instructions, labels);
    }

    public static Integer[] compile(Assembly assembly) {
        ArrayList<Integer> bytecode = new ArrayList<Integer>();

        for (Instruction instruction : assembly.instructions) {
            int argument;
            if (instruction.argument == null) {
                argument = 0;
            } else if (instruction.argument.matches("\\d+")) {
                argument = Integer.parseInt(instruction.argument);
            } else {
                argument = assembly.labels.getOrDefault(instruction.argument, 0);
            }

            if (instruction.opcode != null) {
                bytecode.add(OPCODES.get(instruction.opcode) << 5 | argument);
            } else {
                bytecode.add(argument);
            }
        }

        return bytecode.toArray(new Integer[0]);
    }

    public static int run(Integer[] bytecode) {
        int accumulator = 0;
        int instruction_pointer = 0;
        Integer[] memory = new Integer[MEM];
        Arrays.fill(memory, 0);
        System.arraycopy(bytecode, 0, memory, 0, min(MEM, bytecode.length));

        vm: while (instruction_pointer < MEM) {
            int operation = memory[instruction_pointer] >> 5;
            int argument = memory[instruction_pointer] & 0b11111;
            instruction_pointer++;

            switch (operation) {
                case NOP:
                    continue;
                case LDA:
                    accumulator = memory[argument];
                    break;
                case STA:
                    memory[argument] = accumulator;
                    break;
                case ADD:
                    accumulator = floorMod(accumulator + memory[argument], 256);
                    break;
                case SUB:
                    accumulator = floorMod(accumulator - memory[argument], 256);
                    break;
                case BRZ:
                    if (accumulator == 0) {
                        instruction_pointer = argument;
                    }
                    break;
                case JMP:
                    instruction_pointer = argument;
                    break;
                case STP:
                    break vm;
                default:
                    throw new ComputerZeroException(
                            String.format("error: %d %d", operation, argument));
            }

        }

        return accumulator;
    }

    public static int run(String source) {
        return run(compile(parse(source)));
    }

    public static final List<String> TEST_CASES = Arrays.asList(
            String.join("\n",
                    "        LDA   x",
                    "        ADD   y       ; accumulator = x + y",
                    "        STP",
                    "x:            2",
                    "y:            2"),
            String.join("\n",
                    "loop:   LDA   prodt",
                    "        ADD   x",
                    "        STA   prodt",
                    "        LDA   y",
                    "        SUB   one",
                    "        STA   y",
                    "        BRZ   done",
                    "        JMP   loop",
                    "done:   LDA   prodt   ; to display it",
                    "        STP",
                    "x:            8",
                    "y:            7",
                    "prodt:        0",
                    "one:          1"),
            String.join("\n",
                    "loop:   LDA   n",
                    "        STA   temp",
                    "        ADD   m",
                    "        STA   n",
                    "        LDA   temp",
                    "        STA   m",
                    "        LDA   count",
                    "        SUB   one",
                    "        BRZ   done",
                    "        STA   count",
                    "        JMP   loop",
                    "done:   LDA   n       ; to display it",
                    "        STP",
                    "m:            1",
                    "n:            1",
                    "temp:         0",
                    "count:        8       ; valid range: 1-11",
                    "one:          1"),
            String.join("\n",
                    "start:  LDA   load",
                    "        ADD   car     ; head of list",
                    "        STA   ldcar",
                    "        ADD   one",
                    "        STA   ldcdr   ; next CONS cell",
                    "ldcar:  NOP",
                    "        STA   value",
                    "ldcdr:  NOP",
                    "        BRZ   done    ; 0 stands for NIL",
                    "        STA   car",
                    "        JMP   start",
                    "done:   LDA   value   ; CAR of last CONS",
                    "        STP",
                    "load:   LDA   0",
                    "value:        0",
                    "car:          28",
                    "one:          1",
                    "                    ; order of CONS cells",
                    "                    ; in memory",
                    "                    ; does not matter",
                    "              6",
                    "              0       ; 0 stands for NIL",
                    "              2       ; (CADR ls)",
                    "              26      ; (CDDR ls) -- etc.",
                    "              5",
                    "              20",
                    "              3",
                    "              30",
                    "              1       ; value of (CAR ls)",
                    "              22      ; points to (CDR ls)",
                    "              4",
                    "              24"),
            String.join("\n",
                    "p:            0       ; NOP in first round",
                    "c:            0",
                    "start:  STP           ; wait for p's move",
                    "pmove:  NOP",
                    "        LDA   pmove",
                    "        SUB   cmove",
                    "        BRZ   same",
                    "        LDA   pmove",
                    "        STA   cmove   ; tit for tat",
                    "        BRZ   cdeft",
                    "        LDA   c       ; p defected, c did not",
                    "        ADD   three",
                    "        STA   c",
                    "        JMP   start",
                    "cdeft:  LDA   p",
                    "        ADD   three",
                    "        STA   p",
                    "        JMP   start",
                    "same:   LDA   pmove",
                    "        STA   cmove   ; tit for tat",
                    "        LDA   p",
                    "        ADD   one",
                    "        ADD   pmove",
                    "        STA   p",
                    "        LDA   c",
                    "        ADD   one",
                    "        ADD   pmove",
                    "        STA   c",
                    "        JMP   start",
                    "cmove:        0       ; co-operate initially",
                    "one:          1",
                    "three:        3            "),
            String.join("\n",
                    "LDA  3",
                    "SUB  4",
                    "STP  0",
                    "     0",
                    "     255"),
            String.join("\n",
                    "LDA  3",
                    "SUB  4",
                    "STP  0",
                    "     0",
                    "     1"),
            String.join("\n",
                    "LDA  3",
                    "ADD  4",
                    "STP  0",
                    "     1",
                    "     255")

    );

    public static void main(String[] args) {
        for (String source : TEST_CASES) {
            System.out.println(run(source));
        }
    }
}
Output:
4
56
55
6
0
1
255
0

Julia[edit]

mutable struct ComputerZero
    ip::Int
    ram::Vector{UInt8}
    accum::UInt8
    isready::Bool
end
function ComputerZero(program)
    memory = zeros(UInt8, 32)
    for i in 1:min(32, length(program))
        memory[i] = program[i]
    end
    return ComputerZero(1, memory, 0, true)
end

NOP(c) = (c.ip = mod1(c.ip + 1, 32))
LDA(c) = (c.accum = c.ram[c.ram[c.ip] & 0b00011111 + 1]; c.ip = mod1(c.ip + 1, 32))
STA(c) = (c.ram[c.ram[c.ip] & 0b00011111 + 1] = c.accum; c.ip = mod1(c.ip + 1, 32))
ADD(c) = (c.accum += c.ram[c.ram[c.ip] & 0b00011111 + 1]; c.ip = mod1(c.ip + 1, 32))
SUB(c) = (c.accum -= c.ram[c.ram[c.ip] & 0b00011111 + 1]; c.ip = mod1(c.ip + 1, 32))
BRZ(c) = (c.ip = (c.accum == 0) ? c.ram[c.ip] & 0b00011111 + 1 : mod1(c.ip + 1, 32))
JMP(c) = (c.ip = c.ram[c.ip] & 0b00011111 + 1)
STP(c) = (println("Program completed with accumulator value $(c.accum).\n"); c.isready = false)

const step = [NOP, LDA, STA, ADD, SUB, BRZ, JMP, STP]
const instructions = ["NOP", "LDA", "STA", "ADD", "SUB", "BRZ", "JMP", "STP"]
const assemblywords = Dict(s => i - 1 for (i, s) in pairs(instructions))

function run(compzero::ComputerZero, debug = false)
    while compzero.isready
        instruction = compzero.ram[compzero.ip]
        opcode, operand =  instruction >> 5 + 1, instruction & 0b00011111
        debug && println("op $(instructions[opcode]), operand $operand")
        step[opcode](compzero)
    end
    return compzero.accum
end
run(program::Vector, debug = false) = run(ComputerZero(program), debug)

function compile(text::String)
    bin, lines = UInt8[], 0
    for line in strip.(split(text, "\n"))
        lines += 1
        if isempty(line)
           push!(bin, 0)
        elseif (m = match(r"(\w\w\w)\s+(\d\d?)", line)) != nothing
            push!(bin, UInt8((assemblywords[m.captures[1]] << 5) | parse(UInt8, m.captures[2])))
        elseif (m = match(r"(\w\w\w)", line)) != nothing
            push!(bin, UInt8(assemblywords[m.match] << 5))
        elseif (m = match(r"\d\d?", line)) != nothing
                push!(bin, parse(UInt8, m.match))
        else
            error("Compilation error at line $lines: error parsing <$line>")
        end
    end
    println("Compiled $lines lines.")
    return bin
end

const testprograms = [
    """
        LDA 3
        ADD 4
        STP
        2
        2
    """,
    """
        LDA 12
        ADD 10
        STA 12
        LDA 11
        SUB 13
        STA 11
        BRZ 8
        JMP 0
        LDA 12
        STP
        8
        7
        0
        1
    """,
    """
        LDA 14
        STA 15
        ADD 13
        STA 14
        LDA 15
        STA 13
        LDA 16
        SUB 17
        BRZ 11
        STA 16
        JMP 0
        LDA 14
        STP
        1
        1
        0
        8
        1
    """,
    """
        LDA 13
        ADD 15
        STA 5
        ADD 16
        STA 7
        NOP
        STA 14
        NOP
        BRZ 11
        STA 15
        JMP 0
        LDA 14
        STP
        LDA 0
        0
        28
        1



        6
        0
        2
        26
        5
        20
        3
        30
        1
        22
        4
        24
    """,
    """
        0
        0
        STP
        NOP
        LDA 3
        SUB 29
        BRZ 18
        LDA 3
        STA 29
        BRZ 14
        LDA 1
        ADD 31
        STA 1
        JMP 2
        LDA 0
        ADD 31
        STA 0
        JMP 2
        LDA 3
        STA 29
        LDA 0
        ADD 30
        ADD 3
        STA 0
        LDA 1
        ADD 30
        ADD 3
        STA 1
        JMP 2
        0
        1
        3
    """
]

for t in testprograms
    run(compile(t))
end
Output:
Compiled 6 lines.
Program completed with accumulator value 4.

Compiled 15 lines.
Program completed with accumulator value 56.

Compiled 19 lines.
Program completed with accumulator value 55.

Compiled 33 lines.
Program completed with accumulator value 6. 

Compiled 33 lines.
Program completed with accumulator value 0.

Interpreter version with labels[edit]

Uses the Python examples.

function interpret(text::String)
    ip, accum, isready, ram = 0x1, 0x0, true, zeros(UInt8, 32)
    NOP() = (ip = mod1(ip + 1, 32))
    LDA() = (accum = ram[ram[ip] & 0b00011111 + 1]; ip = mod1(ip + 1, 32))
    STA() = (ram[ram[ip] & 0b00011111 + 1] = accum; ip = mod1(ip + 1, 32))
    ADD() = (accum += ram[ram[ip] & 0b00011111 + 1]; ip = mod1(ip + 1, 32))
    SUB() = (accum -= ram[ram[ip] & 0b00011111 + 1]; ip = mod1(ip + 1, 32))
    BRZ() = (ip = (accum == 0) ? ram[ip] & 0b00011111 + 1 : mod1(ip + 1, 32))
    JMP() = (ip = ram[ip] & 0b00011111 + 1)
    STP() = (println("Program completed with accumulator value $(accum).\n"); isready = false)
    step = [NOP, LDA, STA, ADD, SUB, BRZ, JMP, STP]
    assemblywords = Dict(s => i - 1 for (i, s) in pairs(string.(step)))
    labels = Dict{String, Int}()
    arglabels = Dict{Int, Tuple{Int, String}}()
    for (i, line) in pairs(strip.(split(text, "\n")))
        i > 32 && break
        line = replace(line, r";.*$" => "")  # remove comment
        if occursin(":", line)
            label, line = split(line, ":", limit = 2)
            haskey(labels, label) && error("Duplicate label at line $i")
            labels[strip(label)] = i - 1
        end
        if isempty(line)
           ram[i] = 0
        elseif (m = match(r"(\w\w\w)\s+([a-zA-Z]\w*)", line)) != nothing
            arglabels[i] = (UInt8((assemblywords[m.captures[1]] << 5)), m.captures[2])
        elseif (m = match(r"(\w\w\w)\s+(\d\d*)", line)) != nothing
            ram[i] = UInt8((assemblywords[m.captures[1]] << 5) | parse(UInt8, m.captures[2]))
        elseif (m = match(r"([a-zA-Z]\w*)", line)) != nothing
            ram[i] = UInt8(assemblywords[m.match] << 5)
        elseif (m = match(r"\d\d*", line)) != nothing
                ram[i] = parse(UInt8, m.match)
        else
            error("Compilation error at line $i: error parsing <$line>")
        end
    end
    for (i, t) in arglabels
        ram[i] = t[1] | labels[t[2]]
    end
    while isready
        step[ram[ip] >> 5 + 1]()
    end
    return accum
end

const testprograms = [
    """
        LDA 3
        ADD 4
        STP
        2
        2
    """,
    """
        LDA 12
        ADD 10
        STA 12
        LDA 11
        SUB 13
        STA 11
        BRZ 8
        JMP 0
        LDA 12
        STP
        8
        7
        0
        1
    """,
    """
        LDA 14
        STA 15
        ADD 13
        STA 14
        LDA 15
        STA 13
        LDA 16
        SUB 17
        BRZ 11
        STA 16
        JMP 0
        LDA 14
        STP
        1
        1
        0
        8
        1
    """,
    """
        LDA 13
        ADD 15
        STA 5
        ADD 16
        STA 7
        NOP
        STA 14
        NOP
        BRZ 11
        STA 15
        JMP 0
        LDA 14
        STP
        LDA 0
        0
        28
        1



        6
        0
        2
        26
        5
        20
        3
        30
        1
        22
        4
        24
    """,
    """
        0
        0
        STP
        NOP
        LDA 3
        SUB 29
        BRZ 18
        LDA 3
        STA 29
        BRZ 14
        LDA 1
        ADD 31
        STA 1
        JMP 2
        LDA 0
        ADD 31
        STA 0
        JMP 2
        LDA 3
        STA 29
        LDA 0
        ADD 30
        ADD 3
        STA 0
        LDA 1
        ADD 30
        ADD 3
        STA 1
        JMP 2
        0
        1
        3
    """,
    """\
            LDA   x
            ADD   y       ; accumulator = x + y
            STP
    x:            2
    y:            2
    """,
    """\
    loop:   LDA   prodt
            ADD   x
            STA   prodt
            LDA   y
            SUB   one
            STA   y
            BRZ   done
            JMP   loop
    done:   LDA   prodt   ; to display it
            STP
    x:            8
    y:            7
    prodt:        0
    one:          1
    """,
    """\
    loop:   LDA   n
            STA   temp
            ADD   m
            STA   n
            LDA   temp
            STA   m
            LDA   count
            SUB   one
            BRZ   done
            STA   count
            JMP   loop
    done:   LDA   n       ; to display it
            STP
    m:            1
    n:            1
    temp:         0
    count:        8       ; valid range: 1-11
    one:          1
    """,
    """\
    start:  LDA   load
            ADD   car     ; head of list
            STA   ldcar
            ADD   one
            STA   ldcdr   ; next CONS cell
    ldcar:  NOP
            STA   value
    ldcdr:  NOP
            BRZ   done    ; 0 stands for NIL
            STA   car
            JMP   start
    done:   LDA   value   ; CAR of last CONS
            STP
    load:   LDA   0
    value:        0
    car:          28
    one:          1
                        ; order of CONS cells
                        ; in memory
                        ; does not matter
                6
                0       ; 0 stands for NIL
                2       ; (CADR ls)
                26      ; (CDDR ls) -- etc.
                5
                20
                3
                30
                1       ; value of (CAR ls)
                22      ; points to (CDR ls)
                4
                24
    """,
    """\
    p:            0       ; NOP in first round
    c:            0
    start:  STP           ; wait for p's move
    pmove:  NOP
            LDA   pmove
            SUB   cmove
            BRZ   same
            LDA   pmove
            STA   cmove   ; tit for tat
            BRZ   cdeft
            LDA   c       ; p defected, c did not
            ADD   three
            STA   c
            JMP   start
    cdeft:  LDA   p
            ADD   three
            STA   p
            JMP   start
    same:   LDA   pmove
            STA   cmove   ; tit for tat
            LDA   p
            ADD   one
            ADD   pmove
            STA   p
            LDA   c
            ADD   one
            ADD   pmove
            STA   c
            JMP   start
    cmove:        0       ; co-operate initially
    one:          1
    three:        3
    """,
    """\
    LDA  3
    SUB  4
    STP  0
         0
         255
    """,
    """\
    LDA  3
    SUB  4
    STP  0
         0
         1
    """,
    """\
    LDA  3
    ADD  4
    STP  0
         1
         255
    """,
]

for t in testprograms
    interpret(t)
end
Output:
Program completed with accumulator value 4.

Program completed with accumulator value 56.

Program completed with accumulator value 55.

Program completed with accumulator value 6.

Program completed with accumulator value 0.

Program completed with accumulator value 4.

Program completed with accumulator value 56.

Program completed with accumulator value 55.

Program completed with accumulator value 6.

Program completed with accumulator value 0.

Program completed with accumulator value 1.

Program completed with accumulator value 255.

Program completed with accumulator value 0.

Lua[edit]

Execute (2+2, 7*8)[edit]

Per primary task, just execute first two examples:

vmz = {
  pc = 0,
  acc = 0,
  mem = { [0]=0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0 },
  b2oa = function(byte) return math.floor(byte / 32), byte % 32 end,
  boot = function(self) self.pc, self.acc = 0, 0 for pc=0,31 do self.mem[pc]=0 end return self end,
  load = function(self, bytes) for pc = 0, 31 do self.mem[pc]=bytes[pc] or 0 end return self end,
  clam = function(n) if n<0 then n=n+256 elseif n>255 then n=n-256 end return n end,
  opfn = {[0]=
    function(self,addr) self.pc=self.pc+1 return true end, -- NOP
    function(self,addr) self.acc=self.mem[addr] self.pc=self.pc+1 return true end, -- LDA
    function(self,addr) self.mem[addr]=self.acc self.pc=self.pc+1 return true end, -- STA
    function(self,addr) self.acc=self.clam(self.acc+self.mem[addr]) self.pc=self.pc+1 return true end, -- ADD
    function(self,addr) self.acc=self.clam(self.acc-self.mem[addr]) self.pc=self.pc+1 return true end, -- SUB
    function(self,addr) if (self.acc==0) then self.pc=addr else self.pc=self.pc+1 end return true end, -- BRZ
    function(self,addr) self.pc=addr return true end, -- JMP
    function(self,addr) self.pc=self.pc+1 return false end, -- STP
  },
  step = function(self)
    local oper, addr = self.b2oa(self.mem[self.pc])
    return self.opfn[oper](self,addr)
  end,
  exec = function(self)
    while self.pc < 32 and self:step() do end
    return self
  end,
}
-- object code derived from js sim code
print("2 + 2 = " .. vmz:boot():load({[0]=35,100,224,2,2}):exec().acc)
print("7 x 8 = " .. vmz:boot():load({[0]=44,106,76,43,141,75,168,192,44,224,8,7,0,1}):exec().acc)
Output:
2 + 2 = 4
7 x 8 = 56

Disassembler (7*8)[edit]

Assembly syntax doesn't seem well-specified (except as shown in descriptive text, which is presumably just pseudocode), but next step might be to add a minimal disassembler:

vmz.dism = function(self)
  local mnem, imax = { [0]="NOP", "LDA", "STA", "ADD", "SUB", "BRZ", "JMP", "STP" }
  for pc = 31,0,-1 do imax=pc if self.mem[pc]~=0 then break end end
  local result, pretty = "", "  %3s %2d\n"
  for i = 0, imax do
    local oper, addr = self.b2oa(self.mem[i])
    result = result .. pretty:format(mnem[oper], addr)
  end
  return result
end
vmz:boot():load({[0]=44,106,76,43,141,75,168,192,44,224,8,7,0,1})
print("Disassembly of 7 x 8 (PRE-RUN):")
print(vmz:dism())
print("Disassembly of 7 x 8 (POST-RUN):")
print(vmz:exec():dism())
Output:
Disassembly of 7 x 8 (PRE-RUN):
  LDA 12
  ADD 10
  STA 12
  LDA 11
  SUB 13
  STA 11
  BRZ  8
  JMP  0
  LDA 12
  STP  0
  NOP  8
  NOP  7
  NOP  0
  NOP  1

Disassembly of 7 x 8 (POST-RUN):
  LDA 12
  ADD 10
  STA 12
  LDA 11
  SUB 13
  STA 11
  BRZ  8
  JMP  0
  LDA 12
  STP  0
  NOP  8
  NOP  0
  LDA 24
  NOP  1

Assembler (fibo, list)[edit]

Add an assembler (same minimal syntax as disassembler) for the next two examples:

-- <statement> ::= <opcode> <address>
vmz.assm = function(self, source)
  local function oa2b(oper, addr) return oper * 32 + addr end
  local pc, objc = 0, { NOP=0, LDA=1, STA=2, ADD=3, SUB=4, BRZ=5, JMP=6, STP=7 }
  for oper, addr in source:gmatch("%s*(%a%a%a)%s*(%d*)") do
    self.mem[pc] = oa2b(objc[oper], tonumber(addr) or 0)
    pc = pc + 1
  end    
  return self  
end

srcfibo = "LDA 14 STA 15 ADD 13 STA 14 LDA 15 STA 13 LDA 16 SUB 17 BRZ 11 STA 16 JMP 0 LDA 14 STP 0 NOP 1 NOP 1 NOP 0 NOP 8 NOP 1"
print("Fibonacci = " .. vmz:boot():assm(srcfibo):exec().acc)

srclist = [[
  LDA 13  ADD 15  STA  5  ADD 16  STA  7  NOP  0  STA 14  NOP  0
  BRZ 11  STA 15  JMP  0  LDA 14  STP  0  LDA  0  NOP  0  NOP 28
  NOP  1  NOP  0  NOP  0  NOP  0  NOP  6  NOP  0  NOP  2  NOP 26
  NOP  5  NOP 20  NOP  3  NOP 30  NOP  1  NOP 22  NOP  4  NOP 24
]]
print("Linked list = " .. vmz:boot():assm(srclist):exec().acc)
Output:
Fibonacci = 55
Linked list = 6

Prisoner[edit]

Some additional helper routines, then multiple rounds:

vmz.peek = function(self,addr) return self.mem[addr] end
vmz.poke = function(self,addr,byte) self.mem[addr]=byte end
vmz.entr = function(self,byte) self.mem[self.pc]=byte self.pc=self.pc+1 end
-- derived from the javascript "object code", rather than the descriptive "source code", as they appear to differ
srcpris = [[
  NOP  0 NOP  0 STP  0 NOP  0 LDA  3 SUB 29 BRZ 18 LDA  3 STA 29 BRZ 14 LDA  1 ADD 31 STA  1 JMP  2 LDA  0 ADD 31
  STA  0 JMP  2 LDA  3 STA 29 LDA  1 ADD 30 ADD  3 STA  1 LDA  0 ADD 30 ADD  3 STA  0 JMP  2 NOP  0 NOP  1 NOP  3
]]
print("\nPrisoner (priming) = " .. vmz:boot():assm(srcpris):exec().acc)
-- play five rounds,ie:  poke 0 or 1 into mem[3], pc+=1, exec again
mvnm = {[0]="coop", "defe"}
for r = 1, 5 do
  local move = r%2 -- artificial stupidity?
  vmz:entr(move)
  vmz:exec()
  print("Round: " .. r .. "  Move: " .. mvnm[move] .. "  Player: " .. vmz:peek(0) .. "  Computer: " .. vmz:peek(1))
end
Output:
Prisoner (priming) = 0
Round: 1  Move: defe  Player: 0  Computer: 3
Round: 2  Move: coop  Player: 3  Computer: 3
Round: 3  Move: defe  Player: 3  Computer: 6
Round: 4  Move: coop  Player: 6  Computer: 6
Round: 5  Move: defe  Player: 6  Computer: 9

Phix[edit]

Assumes there is no need for an "assembler", just a runtime interpreter. Output matches Algol 68.

with javascript_semantics
constant NOP = 0b000_00000, -- no operation
         LDA = 0b001_00000, -- load accumulator, a := memory [xxxxx]
         STA = 0b010_00000, -- store accumulator, memory [xxxxx] := a
         ADD = 0b011_00000, -- add, a := a + memory [xxxxx]
         SUB = 0b100_00000, -- subtract, a := a – memory [xxxxx]
         BRZ = 0b101_00000, -- branch on zero, if a = 0 then goto xxxxx
         JMP = 0b110_00000, -- jump, goto xxxxx
         STP = 0b111_00000, -- stop
         OP  = 0b111_00000, -- operator mask
         ARG = 0b000_11111  -- memory location (0 based)

procedure execute(string name, sequence program)
    sequence memory = deep_copy(program)
    integer pc = 1, a = 0
    while true do
        integer ppc = memory[pc],
                op = and_bitsu(ppc,OP),
                arg = and_bits(ppc,ARG)+1
        pc += 1
        switch op do
            case NOP:   break
            case LDA:   a = memory[arg]
            case STA:   memory[arg] = a
            case ADD:   a = and_bitsu(a+memory[arg],#FF)
            case SUB:   a = and_bitsu(a-memory[arg],#FF)
            case BRZ:   if a=0 then pc = arg end if
            case JMP:   pc = arg
            case STP:   printf(1,"%12s: %3d\n",{name,a})
                        return
        end switch
    end while
end procedure

execute("2+2",{LDA+3, ADD+4, STP, 2,2})
execute("7*8",{LDA+12, ADD+10, STA+12, LDA+11, SUB+13, STA+11, BRZ+8, JMP+0,
               LDA+12, STP, 8,7,0,1})
execute("fibonacci",{LDA+14, STA+15, ADD+13, STA+14, LDA+15, STA+13, LDA+16,
                     SUB+17, BRZ+11, STA+16, JMP+0,  LDA+14, STP, 1,1,0,8,1})
execute("linkedList",{LDA+13, ADD+15, STA+5, ADD+16, STA+7, NOP, STA+14, NOP,
                      BRZ+11, STA+15, JMP+0, LDA+14, STP, LDA+0, 0,28,1,0,0,
                      0,6,0,2,26,5,20,3,30,1,22,4,24})
execute("prisoner",{NOP, NOP, STP, 0, LDA+3, SUB+29, BRZ+18, LDA+3, STA+29, 
                    BRZ+14, LDA+1, ADD+31, STA+1, JMP+2, LDA+0, ADD+31, STA+0,
                    JMP+2, LDA+3, STA+29, LDA+1, ADD+30, ADD+3, STA+1, LDA+0,
                    ADD+30, ADD+3, STA+0, JMP+2, 0, 1, 3})
-- subtractions yielding negative results
execute("0-255",{LDA+3,SUB+4,STP, 0,255})
execute("0-1",{LDA+3, SUB+4, STP, 0,1})
-- overflow on addition
execute("1+255",{LDA+3, ADD+4, STP, 1, 255})

You could of course define the programs using (say) 0b001_00011 instead of LDA+3.

Output:
         2+2:   4
         7*8:  56
   fibonacci:  55
  linkedList:   6
    prisoner:   0
       0-255:   1
         0-1: 255
       1+255:   0

Python[edit]

"""Computer/zero Assembly emulator. Requires Python >= 3.7"""

import re

from typing import Dict
from typing import Iterable
from typing import List
from typing import NamedTuple
from typing import Optional
from typing import Tuple


NOP = 0b000
LDA = 0b001
STA = 0b010
ADD = 0b011
SUB = 0b100
BRZ = 0b101
JMP = 0b110
STP = 0b111

OPCODES = {
    "NOP": NOP,
    "LDA": LDA,
    "STA": STA,
    "ADD": ADD,
    "SUB": SUB,
    "BRZ": BRZ,
    "JMP": JMP,
    "STP": STP,
}

RE_INSTRUCTION = re.compile(
    r"\s*"
    r"(?:(?P<label>\w+):)?"
    r"\s*"
    rf"(?P<opcode>{'|'.join(OPCODES)})?"
    r"\s*"
    r"(?P<argument>\w+)?"
    r"\s*"
    r"(?:;(?P<comment>[\w\s]+))?"
)


class AssemblySyntaxError(Exception):
    pass


class Instruction(NamedTuple):
    label: Optional[str]
    opcode: Optional[str]
    argument: Optional[str]
    comment: Optional[str]


def parse(assembly: str) -> Tuple[List[Instruction], Dict[str, int]]:
    instructions: List[Instruction] = []
    labels: Dict[str, int] = {}
    linenum: int = 0

    for line in assembly.split("\n"):
        match = RE_INSTRUCTION.match(line)

        if not match:
            raise AssemblySyntaxError(f"{line}: {linenum}")

        instructions.append(Instruction(**match.groupdict()))
        label = match.group(1)
        if label:
            labels[label] = linenum

        linenum += 1

    return instructions, labels


def compile(instructions: List[Instruction], labels: Dict[str, int]) -> Iterable[int]:
    for instruction in instructions:
        if instruction.argument is None:
            argument = 0
        elif instruction.argument.isnumeric():
            argument = int(instruction.argument)
        else:
            argument = labels[instruction.argument]

        if instruction.opcode:
            yield OPCODES[instruction.opcode] << 5 | argument
        else:
            yield argument


def run(bytecode: bytes) -> int:
    accumulator = 0
    program_counter = 0
    memory = list(bytecode)[:32] + [0 for _ in range(32 - len(bytecode))]

    while program_counter < 32:
        operation = memory[program_counter] >> 5
        argument = memory[program_counter] & 0b11111
        program_counter += 1

        if operation == NOP:
            continue
        elif operation == LDA:
            accumulator = memory[argument]
        elif operation == STA:
            memory[argument] = accumulator
        elif operation == ADD:
            accumulator = (accumulator + memory[argument]) % 256
        elif operation == SUB:
            accumulator = (accumulator - memory[argument]) % 256
        elif operation == BRZ:
            if accumulator == 0:
                program_counter = argument
        elif operation == JMP:
            program_counter = argument
        elif operation == STP:
            break
        else:
            raise Exception(f"error: {operation} {argument}")

    return accumulator


SAMPLES = [
    """\
            LDA   x
            ADD   y       ; accumulator = x + y
            STP
    x:            2
    y:            2
    """,
    """\
    loop:   LDA   prodt
            ADD   x
            STA   prodt
            LDA   y
            SUB   one
            STA   y
            BRZ   done
            JMP   loop
    done:   LDA   prodt   ; to display it
            STP
    x:            8
    y:            7
    prodt:        0
    one:          1
    """,
    """\
    loop:   LDA   n
            STA   temp
            ADD   m
            STA   n
            LDA   temp
            STA   m
            LDA   count
            SUB   one
            BRZ   done
            STA   count
            JMP   loop
    done:   LDA   n       ; to display it
            STP
    m:            1
    n:            1
    temp:         0
    count:        8       ; valid range: 1-11
    one:          1
    """,
    """\
    start:  LDA   load
            ADD   car     ; head of list
            STA   ldcar
            ADD   one
            STA   ldcdr   ; next CONS cell
    ldcar:  NOP
            STA   value
    ldcdr:  NOP
            BRZ   done    ; 0 stands for NIL
            STA   car
            JMP   start
    done:   LDA   value   ; CAR of last CONS
            STP
    load:   LDA   0
    value:        0
    car:          28
    one:          1
                        ; order of CONS cells
                        ; in memory
                        ; does not matter
                6
                0       ; 0 stands for NIL
                2       ; (CADR ls)
                26      ; (CDDR ls) -- etc.
                5
                20
                3
                30
                1       ; value of (CAR ls)
                22      ; points to (CDR ls)
                4
                24
    """,
    """\
    p:            0       ; NOP in first round
    c:            0
    start:  STP           ; wait for p's move
    pmove:  NOP
            LDA   pmove
            SUB   cmove
            BRZ   same
            LDA   pmove
            STA   cmove   ; tit for tat
            BRZ   cdeft
            LDA   c       ; p defected, c did not
            ADD   three
            STA   c
            JMP   start
    cdeft:  LDA   p
            ADD   three
            STA   p
            JMP   start
    same:   LDA   pmove
            STA   cmove   ; tit for tat
            LDA   p
            ADD   one
            ADD   pmove
            STA   p
            LDA   c
            ADD   one
            ADD   pmove
            STA   c
            JMP   start
    cmove:        0       ; co-operate initially
    one:          1
    three:        3
    """,
    """\
    LDA  3
    SUB  4
    STP  0
         0
         255
    """,
    """\
    LDA  3
    SUB  4
    STP  0
         0
         1
    """,
    """\
    LDA  3
    ADD  4
    STP  0
         1
         255
    """,
]


def main() -> None:
    for sample in SAMPLES:
        instructions, labels = parse(sample)
        bytecode = bytes(compile(instructions, labels))
        result = run(bytecode)
        print(result)


if __name__ == "__main__":
    main()
Output:
4
56
55
6
0
1
255
0

Wren[edit]

As I'm unclear whether the interpreter should be able to deal with labels, the programs all use literal memory addresses for now. Output is in decimal.

Although I've entered the fifth program, it just returns 0 when reaching the STP instruction. I'm unclear how we can make it interactive without having another instruction though possibly, if STP had address bits other than 0, this could signal that user input was required.

var NOP = 0
var LDA = 1
var STA = 2
var ADD = 3
var SUB = 4
var BRZ = 5
var JMP = 6
var STP = 7

var ops = {"NOP": NOP, "LDA": LDA, "STA": STA, "ADD": ADD,
           "SUB": SUB, "BRZ": BRZ, "JMP": JMP, "STP": STP}

var load = Fn.new { |prog|
    var mem = List.filled(32, 0)
    var lines = prog.trimEnd().split("\n")
    for (i in 0...lines.count) {
        var line = lines[i].trim()
        var split = line.split(" ")
        var instr = split[0]
        var addr = 0
        if (split.count == 2) addr = Num.fromString(split[1])
        if (ops[instr]) {
            mem[i] = ops[instr] * 32 + addr
        } else {
            var v = Num.fromString(instr)
            if (v) mem[i] = v
        }
    }
    return mem
}

var output = Fn.new { |acc|
    System.print(acc)
}

var interp = Fn.new { |prog|
    var acc = 0
    var pc = 0
    var mem = load.call(prog)
    while (true) {
        var instr = mem[pc] >> 5
        var addr  = mem[pc] % 32
        pc = pc + 1
        if (instr == LDA) {
            acc = mem[addr]
        } else if (instr == STA) {
            mem[addr] = acc
        } else if (instr == ADD) {
            acc = acc + mem[addr]
            if (acc > 255) acc = acc - 256
        } else if (instr == SUB) {
            acc = acc - mem[addr]
            if (acc < 0) acc = acc + 256
        } else if (instr == BRZ) {
            if (acc == 0) pc = addr
        } else if (instr == JMP) {
            pc = addr
        }
        if (instr == STP || pc > 31) break
    }
    output.call(acc)
}

var progs = [
    """
        LDA 3
        ADD 4
        STP
        2
        2
    """,
    """
        LDA 12
        ADD 10
        STA 12
        LDA 11
        SUB 13
        STA 11
        BRZ 8
        JMP 0
        LDA 12
        STP
        8
        7
        0
        1
    """,
    """
        LDA 14
        STA 15
        ADD 13
        STA 14
        LDA 15
        STA 13
        LDA 16
        SUB 17
        BRZ 11
        STA 16
        JMP 0
        LDA 14
        STP
        1
        1
        0
        8
        1
    """,
    """
        LDA 13
        ADD 15
        STA 5
        ADD 16
        STA 7
        NOP
        STA 14
        NOP
        BRZ 11
        STA 15
        JMP 0
        LDA 14
        STP
        LDA 0
        0
        28
        1



        6
        0
        2
        26
        5
        20
        3
        30
        1
        22
        4
        24
    """,
    """
        0
        0
        STP
        NOP
        LDA 3
        SUB 29
        BRZ 18
        LDA 3
        STA 29
        BRZ 14
        LDA 1
        ADD 31
        STA 1
        JMP 2
        LDA 0
        ADD 31
        STA 0
        JMP 2
        LDA 3
        STA 29
        LDA 0
        ADD 30
        ADD 3
        STA 0
        LDA 1
        ADD 30
        ADD 3
        STA 1
        JMP 2
        0
        1
        3
    """
]
for (prog in progs) interp.call(prog)
Output:
4
56
55
6
0

Z80 Assembly[edit]

Output is in hexadecimal but is otherwise correct.

org &1000
PrintChar equ &BB5A

;reg usage:
;DE = VM'S Program Counter
;IXL = VM's Accumulator
main:
	ld ixl,0
	ld de,Computer_Zero_RAM_2_plus_2
	call Computer_Zero_VM
	ld a,ixl
	call ShowHex	;output to Amstrad CPC's screen
	call NewLine
	
	ld ixl,0
	ld de,Computer_Zero_RAM_7x8
	call Computer_Zero_VM
	ld a,ixl
	jp ShowHex	;output and return to basic.
	
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;these two functions are related to displaying the output
;	and have nothing to do with the virtual machine itself.
ShowHex:	
		push af
			and %11110000
			rrca
			rrca
			rrca
			rrca
			call PrintHexChar
		pop af
		and %00001111
		;call PrintHexChar
		;execution flows into it naturally.
PrintHexChar:
		;converts hex to ascii
		or a	;Clear Carry Flag
		daa
		add a,&F0
		adc a,&40
		jp PrintChar
		
NewLine:
	push af
		ld a,13
		call PrintChar
		ld a,10
		call PrintChar
	pop af
	ret
	
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Computer_Zero_VM:
	ld a,(de)			;opcode fetch
	call UnpackOpcode	;stores opcode in B, operand in C
	push de
		ld de,Opcode_Table
		ld a,b
		rlca		;index times 2 for word data
		
		ld e,a
		ld a,(de)
		ld L,a
		inc de
		ld a,(de)
		ld h,a		;LD HL,(DE)
		
	pop de
	jp (hl)
;register state after this jump:
;DE = program counter
;HL = address of instruction implementation
;C = operand of the instruction we're about to execute
;IXL = accumulator



	overhead:
	ld a,e
	inc a
	and %00011111		
	;ensures we stay within the 32 byte address space.
	ld e,a
	jp Computer_Zero_VM


	UnpackOpcode:
	push af
		and %11100000
		rlca
		rlca
		rlca
		ld b,a		;opcode in B
	pop af
	and %00011111
	ld c,a			;operand in C
	dummy:
	ret



align 256	;ensures the following table is page-aligned
;this lets us index it much faster.
Opcode_Table:	
	dw vmNOP
	dw vmLDA
	dw vmSTA
	dw vmADD
	dw vmSUB
	dw vmBRZ
	dw vmJMP
	dw vmSTP

vmNOP:
	jp overhead	;do nothing
vmLDA:
	push de
	ld e,c		;offset DE by the operand
	ld a,(de)	;load from that address
	ld ixl,a	;and store it in the accumulator
	pop de
	jp overhead
vmSTA:
	push de
	ld e,c		;offset DE by the operand
	ld a,ixl	;get the accumulator
	ld (de),a	;store it into (DE)	
	pop de
	jp overhead
vmADD:
	push de		
	ld e,c		;offset DE by the operand
	ld a,(de)	;load from that address
	add ixl		;and add that value to the accumulator
	ld ixl,a	;then set the new accumulator
	pop de
	jp overhead
vmSUB:
	push de
	ld e,c		;offset DE by the operand
	ld a,(de)
	ld b,a
	ld a,ixl
	sub b
	ld ixl,a
	pop de
	noBRZ:
	jp overhead
vmBRZ:
	ld a,ixl
	or a
	jr nz, noBRZ
vmJMP:
	ld e,c
	jp Computer_Zero_VM
vmSTP:
	ret		;return to main
	
align 256
Computer_Zero_RAM_2_plus_2:
	db %00100011,%01100100
	db %11100000,%00000010
	db %00000010,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
align 256
Computer_Zero_RAM_7x8:
	db %00101100,%01101010
	db %01001100,%00101011
	db %10001101,%01001011
	db %10101000,%11000000
	db %00101100,%11100000
	db %00001000,%00000111
	db %00000000,%00000001
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
	db %00000000,%00000000
Output:
04
38