private Sequence sequence(final int foundAt) {
            int delta = ((foundAt & P_MASK) - (_lastInsertAt & P_MASK));
            if ((foundAt & EXACT_MASK) == 0 && delta == KEYBLOCK_LENGTH) {
                return Sequence.FORWARD;
            }
            if ((foundAt & EXACT_MASK) == 0 && delta == 0) {
                return Sequence.REVERSE;
            }
            return Sequence.NONE;
        }