function convert (b) {
  var gb = 1 << 30, mb = 1 << 20, kb = 1 << 10;
  if (b >= gb) return (Math.round(b / gb * 100) / 100) + 'gb';
  if (b >= mb) return (Math.round(b / mb * 100) / 100) + 'mb';
  if (b >= kb) return (Math.round(b / kb * 100) / 100) + 'kb';
  return b + 'b';
}
convert bytes into string.

@param {Number} b - bytes to convert
@return {String}
@api public