docs: def int_to_string( x ):
    """Convert integer x into a string of bytes, as per X9.62."""
    assert x >= 0
    if x == 0: return b('\0')
    result = []
    while x:
      ordinal = x & 0xFF
      result.append(int2byte(ordinal))
      x >>= 8
  
    result.reverse()
    return b('').join(result)