How to measure distance between two data

when the user write on the keyboard there is a software program capture the data input and measure the trigraphs duration (time) then i will make a sorter to sort those trigraphs duration according thair times ,so i need their time for ordering them only, but trust me i don't know how i give the trigraphs to the fpga . i know the procedures but can't make it reall in fpga board. should you suggest me away to make it??