800) {
      lastPos = i + 1;
      out += hexTable[0xC0 | (c >> 6)] +
             hexTable[0x80 | (c & 0x3F)];
      continue;
    }
    if (c < 0xD800 || c >= 0xE000) {
      lastPos = i + 1;
      out += hexTable[0xE0 | (c >> 12)] +
             hexTable[0x80 | ((c >> 6) & 0x3F)] +
             hexTable[0x80 | (c & 0x3F)];
      continue;
    }
    // Surrogate pair
    ++i;

    // This branch should never happen because all URLSearchParams entries
    // should already be converted to USVString. But, included for
    // completion's sake anyway.
    if (i >= len)
      throw new ERR_INVALID_URI();

    const c2 = StringPrototypeCharCodeAt(str, i) & 0x3FF;

    lastPos = i + 1;
    c = 0x10000 + (((c & 0x3FF) << 10) | c2);
    out += hexTable[0xF0 | (c >> 18)] +
           hexTable[0x80 | ((c >> 12) & 0x3F)] +
           hexTable[0x80 | ((c >> 6) & 0x3F)] +
           hexTable[0x80 | (c & 0x3F)];
  }
  if (lastPos === 0)
    return str;
  if (lastPos < len)
    return out + StringPrototypeSlice(str, lastPos);
  return out;
}

module.exports = {
  encodeStr,
  hexTable,
  isHexTable,
};