BrainFuck 解释器

brainfuck.js

function getMatchingBra(code) {
    var stack = [];
    var bra = [];
    for(var i = 0; i < code.length; i++) bra.push(-1);
    for(var i = 0; i < code.length; i++) {
        if(code[i] === '[') {
            stack.push(i);
        } else if(code[i] === ']') {
            bra[i] = stack.pop();
            bra[bra[i]] = i;
        }
    }
    return bra;
}

function brainFuck(code, input) {
    var inputPos = 0;
    var commandPos = 0;
    var pointerPos = 0;
    var bytes = [ 0 ];
    var output = "";
    var matching = getMatchingBra(code);

    while(commandPos < code.length) {
        switch(code[commandPos]) {
            case '>': {
                pointerPos++;
                if(undefined === bytes[pointerPos]) {
                    bytes.push(0);
                }
                break;
            }
            case '<': {
                pointerPos--;
                if(0 > pointerPos) {
                    bytes.unshift(0);
                    pointerPos = 0;
                }
                break;
            }
            case '+': {
                bytes[pointerPos] = (bytes[pointerPos] + 1) % 256;
                break;
            }
            case '-': {
                bytes[pointerPos]--;
                if(bytes[pointerPos] < 0) bytes[pointerPos] = 0;
                break;
            }
            case '.': {
                output += String.fromCharCode(bytes[pointerPos]);
                break;
            }
            case ',': {
                var temp = input.charCodeAt(inputPos++);
                bytes[pointerPos] = temp;
                break;
            }
            case '[': {
                if(!bytes[pointerPos]) {
                    commandPos = matching[commandPos];
                }
                break;
            }
            case ']': {
                if(bytes[pointerPos]) {
                    commandPos = matching[commandPos];
                }
                break;
            }
        }
        commandPos++;
    }

    return output;
}
var out = brainFuck('+++++++[>+++++[>++>+<<-]>>>+>++>++<<<<<<-]>>+++.[->+<]>.+++.[->+<]>.>[-<->]<---.>>[-<<->>]<<--.');
console.log(out);