Pads data to the multiplies of 8 bytes.

       This makes x86_64 faster and prevents
       undefined behavior on other platforms

def padto8(data):
    """Pads data to the multiplies of 8 bytes.

       This makes x86_64 faster and prevents
       undefined behavior on other platforms"""
    length = len(data)
    return data + b'\xdb' * (roundto8(length) - length)