Execute Computer/Zero
You are encouraged to solve this task according to the task description, using any language you may know.
- 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
STPopcode 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
<lang algol68>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 </lang>
- Output:
2+2: 4
7*8: 56
fibonacci: 55
linkedList: 6
prisoner: 0
0-255: 1
0-1: 255
1+255: 0
J
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:
<lang J>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=: Template:'cod val'=. 0 32
exec=: {{
pc=: acc=: 0 while. 0<:pc do. exec1 end. acc
}}</lang>
With this implementation, we can assemble and run representations of the five suggested programs:
<lang J> 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</lang>
Alternate approach
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:
<lang J>opcode=: {{
(m+{.y),}.y
x,m opcode y
}}
(Template:((x)=: y opcode)0&>32*i.@#);:'NOP LDA STA ADD SUB BRZ JMP STP'
exec1=: Template:'cod val'=. 0 32
exec=: {{
mem=: 32{.y
pc=: acc=: 0
while. 0<:pc do. exec1 end.
acc
}}</lang>
and:
<lang J> 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</lang>
Java
<lang python>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));
}
}
} </lang>
- Output:
4 56 55 6 0 1 255 0
Julia
<lang ruby>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
</lang>
- 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
Uses the Python examples. <lang ruby>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
</lang>
- 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
Execute (2+2, 7*8)
Per primary task, just execute first two examples: <lang lua>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)</lang>
- Output:
2 + 2 = 4 7 x 8 = 56
Disassembler (7*8)
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: <lang lua>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())</lang>
- 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)
Add an assembler (same minimal syntax as disassembler) for the next two examples: <lang lua>-- <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)</lang>
- Output:
Fibonacci = 55 Linked list = 6
Prisoner
Some additional helper routines, then multiple rounds: <lang lua>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</lang>
- 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
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
<lang python>"""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()
</lang>
- Output:
4 56 55 6 0 1 255 0
Wren
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. <lang ecmascript>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)</lang>
- Output:
4 56 55 6 0
Z80 Assembly
Output is in hexadecimal but is otherwise correct. <lang z80>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</lang>
- Output:
04 38