This process is usually referred to as backward search.
let SA[l i , r i ] be the interval corresponding to the suffixes in we compute RANK(T bwt , l i , c), the number of times symbol c occurs before l i and RANK(T bwt , r i + 1, c), the number of occurrences of c in we additionally store the starting positions C s of all suffixes for each symbol s in Σ at a negligible cost of σ log n bits.