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1e2aae8095
The idea is to avoid std::map lookup for each CellRef. Instead generate a sequence of added and removed RefNums into a vector then order them by RefNum using a stable sort that preserves relative order of elements with the same RefNum. RefIDs are stored in a different vector to avoid std::string move ctor calls when swapping elements while sorting. Reversed iteration over added and removed RefNums for each unique RefNum is an equivalent to what map-based algorithm produces. The main benefit from sorting a vector is a data locality that means less cache misses for each access. Reduces ESMStore::countRecords perf cycles by 25%.