def encode(data):
    if not data:
        return
    l = len(data)
    if l % 2 != 0:
        return None
    ret = bytearray()
    for i in range(0, l, 2):
        usTmp = data[i] << 8
        usTmp += data[i + 1]
        ucByte = ((usTmp >> 12) & 0xff)

        if i >= l - 2:
            ucByte |= ((1 << 5) & 0xff)
        if i < 2:
            ucByte |= ((1 << 6) & 0xff)
        a = ((2 << 6) & 0xff)
        a += ((usTmp >> 6) & 0x3f)
        b = ((3 << 6) & 0xff)
        b += (usTmp & 0x3f)
        ret.append(ucByte)
        ret.append(a)
        ret.append(b)
    return ret

def decode(data):
    if not data:
        return
    l = len(data)
    if l % 3 != 0:
        return None
    ret = bytearray()
    for i in range(0, l, 3):
        val = data[i]
        usTmp = (val & 0x0f)

        usTmp <<= 6
        val = data[i + 1]
        a = (val & 0x3f)
        usTmp += a

        usTmp <<= 6
        val = data[i + 2]
        b = (val & 0x3f)
        usTmp += b

        a = (usTmp >> 8) & 0xff
        b = (usTmp & 0xff)
        ret.append(a)
        ret.append(b)
    return ret