public BitString24 ReadBitString24(byte tag = 255)
{
_ensureTag(tag, ApplicationTag.BitString);
_ensureLength(2, 8);
byte unused = _reader.ReadByte();
byte length = (byte)((_length - 1) * 8 - unused);
ulong flags = _reader.ReadByte();
for (int i = 1; i < _length - 1; i++)
{
flags <<= 8;
flags |= _reader.ReadByte();
}
flags >>= (length - 4) * 8;
return new BitString24(length, (uint)flags);
}