// first = true - find first occurance
// first = false - find last occurance
// first = undefined - first found

function binarySearch(array, x, first) {
  var start = 0, end = array.length - 1, mid = 0, result = -1;
  while (start <= end) {
    mid = Math.floor((start + end) / 2);
    if (array[mid] == x) {
      result = mid;
      if (typeof first === 'undefined') {
        return result;
      } else if (first === true) {
        end = mid - 1;
      } else if (first === false) {
        start = mid + 1;
      }
    } else if (x < array[mid]) {
      end = mid - 1;
    } else {
      start = mid + 1;
    }
  }
  return result;
}