===== ISTEM =====
Solve the following programming task.

TASK: TIK Register Machine

Write a function 'runTik(program)' that runs a program written in TIK, a small made-up language, and returns an array of the numbers it outputs.

Program text:
- Instructions are separated by newlines. Leading and trailing spaces on a line are ignored.
- Lines that are empty (or only spaces) and lines whose first non-space character is '#' are ignored and are not instructions.
- Within an instruction, tokens are separated by one or more spaces.

Machine:
- There are four registers named a, b, c and d. All start at 0.
- Every value stored in a register is reduced to the range 0..999 by taking it modulo 1000, always giving a non-negative result (for example -1 becomes 999 and 1003 becomes 3).
- An integer literal is an optional '-' followed by one or more digits ('+5' and '5.0' are not valid).
- An operand written as X below is either a register name or an integer literal. Its value is the register's value, or the literal reduced to 0..999 in the same way.

Instructions (R must be a register name, N must be an integer literal):
- set R X: R becomes the value of X.
- add R X: R becomes R plus the value of X.
- mul R X: R becomes R times the value of X.
- out X: appends the value of X to the output.
- jmp X N: if the value of X is not 0, the next instruction is the one N instructions away from this one (N may be negative; ignored lines are not counted). Otherwise execution continues with the next instruction.
Instruction names and register names are lowercase; anything else is invalid.

Running:
- Before running anything, check the whole program. If any line that is not ignored is not a valid instruction (unknown name, wrong number of operands, or an invalid register, literal or operand), throw an Error whose message is 'bad instruction at line K', where K is the 1-based line number of the first such line in the original text, counting ignored lines too. In that case nothing is run.
- Execution starts at the first instruction and stops normally when the next instruction position is before the first instruction or after the last one.
- A program may execute at most 10,000 instructions. If it has not stopped after executing 10,000 instructions, throw an Error with the message 'step limit'.

STARTER CODE (javascript):
function runTik(program) {
  // Write your code here
}

module.exports = { runTik };


RULES:
- Keep the function name and signature EXACTLY as given.
- Return working code only. No explanations.
- Put the code in a single ``` block.
- Try to solve it first. If you genuinely cannot, write only this single
  line instead of producing faulty code: CANNOT_SOLVE

===== HAM YANIT =====
```javascript
function runTik(program) {
    const lines = program.split('\n');
    const registers = { a: 0, b: 0, c: 0, d: 0 };
    const validRegisters = new Set(['a', 'b', 'c', 'd']);

    function mod(n) {
        return ((n % 1000) + 1000) % 1000;
    }

    function isLiteral(s) {
        return /^-?\d+$/.test(s);
    }

    function parseOperand(op) {
        if (validRegisters.has(op)) return registers[op];
        if (isLiteral(op)) return mod(parseInt(op, 10));
        return null;
    }

    const instructions = [];
    for (let i = 0; i < lines.length; i++) {
        let line = lines[i].trim();
        if (line === '' || line.startsWith('#')) continue;

        const parts = line.split(/\s+/);
        const cmd = parts[0];
        let valid = false;

        if ((cmd === 'set' || cmd === 'add' || cmd === 'mul') && parts.length === 3) {
            if (validRegisters.has(parts[1]) && parseOperand(parts[2]) !== null) valid = true;
        } else if (cmd === 'out' && parts.length === 2) {
            if (parseOperand(parts[1]) !== null) valid = true;
        } else if (cmd === 'jmp' && parts.length === 3) {
            if (parseOperand(parts[1]) !== null && isLiteral(parts[2])) valid = true;
        }

        if (!valid) throw new Error(`bad instruction at line ${i + 1}`);
        instructions.push({ cmd, args: parts.slice(1), lineNum: i + 1 });
    }

    const output = [];
    let pc = 0;
    let steps = 0;

    while (pc >= 0 && pc < instructions.length) {
        if (++steps > 10000) throw new Error('step limit');

        const { cmd, args } = instructions[pc];

        if (cmd === 'set') {
            registers[args[0]] = parseOperand(args[1]);
            pc++;
        } else if (cmd === 'add') {
            registers[args[0]] = mod(registers[args[0]] + parseOperand(args[1]));
            pc++;
        } else if (cmd === 'mul') {
            registers[args[0]] = mod(registers[args[0]] * parseOperand(args[1]));
            pc++;
        } else if (cmd === 'out') {
            output.push(parseOperand(args[0]));
            pc++;
        } else if (cmd === 'jmp') {
            if (parseOperand(args[0]) !== 0) {
                pc += parseInt(args[1], 10);
            } else {
                pc++;
            }
        }
    }

    return output;
}
```