gistfile1.js

memoArr = {};
var charset = "A%sB$nC-(D;)Ea0Fb1Gc2Hd3Ie4Jf5Kg6Lh7Mi8Nj9OkPlQmRnSoTpUqVrWsXtYuZvwxyz"; // default gdb-peda charset
function deBruijn (charset, maxlen, n) {
    var k = charset.length;
    var a = [];
    for (var i = 0; i < k * n; i++) a.push(0);

    if (maxlen.toString() in memoArr)
        return memoArr[maxlen.toString()];
    for (var k in memoArr) {
        if (memoArr[k].length >= maxlen)
            return memoArr[k].substr(0,maxlen);
    } 
    
    var sequence = [];
    (function db (t, p) {
        if (sequence.length > maxlen) return;
        if (t > n) {
            if (n % p !== 0) return;
            for (var j = 1; j <= p; j++) {
                sequence.push(charset[a[j]]);
            }
            return;
        }
        
        a[t] = a[t-p];
        db(t + 1, p);
        for (var j = a[t-p] + 1; j < k; j++) {
            a[t] = j;
            db(t + 1, t);
        }
    })(1,1);
    memoArr[maxlen.toString()] = sequence.join('');
    return memoArr[maxlen.toString()];
}; 
var last_searched_val = "";
var max_search_len = 0x9000;
function findOccurrence(n, val) {
  var len = 0x3000; // this value works quick enough on my galaxy s5
  while (true) {
    len += 0x2000;
    var pat = deBruijn(charset,len,3);
    var pos = pat.indexOf(val);
    if (pos !== -1) return pos;
    if (len >= max_search_len) return -1;
  }
};

// http://stackoverflow.com/a/2838358/436914
function selectElementText(el, win) {
    win = win || window;
    var doc = win.document, sel, range;
    if (win.getSelection && doc.createRange) {
        sel = win.getSelection();
        range = doc.createRange();
        range.selectNodeContents(el);
        sel.removeAllRanges();
        sel.addRange(range);
    } else if (doc.body.createTextRange) {
        range = doc.body.createTextRange();
        range.moveToElementText(el);
        range.select();
    }
}
function getPattern() {
    var k = document.getElementById('patlen').value;
    k = parseInt(k, 10)
    if (isNaN(k)) k = parseInt(k, 16);
    if (isNaN(k)) k = 0x8000;
    
    var patBox = document.getElementById('pattern');
    patBox.innerHTML = deBruijn(charset,k,3);
    selectElementText(patBox);
}

function goSearch() {
    var k = document.getElementById('searchval').value;
    if (k.substr(0,2) === "0x") {
        // assume they're pasting a 32bit hex value out of GDB or something
        var hexVal = k.substr(2);
        if (hexVal.length % 4 !== 0) {
            alert("hey it looks like you gave us a hex value \"0x01234ABCD...\" but for that to remotely work we recommend you make it four bytes long.");
            return;
        }
        // convert it to chars, swap the order.
        var bytes = x.match(/../g).reverse();
        var buildStr = "";
        for (var v in bytes) {
            try {
                buildStr += parseInt(v,16);
            } catch(e) {
                alert("tried to treat your input as 32bit little endian integer and convert to chars, but it wasn't valid.");
                return;
            }
        }
        k = buildStr;
    }
    
    // we'll let them enter 8/16/32 anyways...
    if ((k.length%4 != 0)) {
        alert("you should probably be searching for 4 ascii chars at a time. try again.");
        return;
    }
    
    if (k === last_searched_val) {
        max_search_len += 0x10000;
    }
    
    last_searched_val = k;
    var found = findOccurrence(3, k);
    if (found === -1) {
        alert("couldn't find your input. hitting find again with the same input will search harder but make your browser chug.");
        return;
    }
    
    document.getElementById('searchresult').innerHTML = "Found value at offset " + found;
}