2.6.5 Converting Length Header and Position Slot into Length/Position Header Values
The length/position header is the stage that correlates the match position with the match length (using only the most significant bits) and is created by combining the length header and the position slot, as follows:
len_pos_header ←(position_slot << 3) + length_header
This operation creates a unique value for every combination of match length 2, 3, 4, 5, 6, 7, 8 with every possible position slot. The remaining match lengths greater than 8 are all lumped together and, as a group, are correlated with every possible position slot.