C++ Optimize if/else condition

Question

I have a single line of code, that consumes 25% - 30% of the runtime of my application. It is a less-than comparator for an std::set (the set is implemented with a Red-Black-Tre

Answer 1

An easy solution is precompute a sort-identifier comprised of the cost as most significant and the id as the rest.

E.g.,

struct Entry
{
    double cost_;
    long id_;
    long long sortingId_;

  // some other vars

    Entry( double cost, float id )
        : cost_( cost ), id_( id ), sortingId_( 1e9*100*cost + id )
    {} 
};

Adjust sortingId_ value based on what you can assume about the value ranges.

Then, now just sort on sortingId_.

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Or as variation of the same idea, if you can't make suitable assumptions about the data, then consider preparing data especially for memcmp.

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For a higher level solution, remember that std::set::insert has an overload with a hint argument. If your data is already in near sorted order, that might seriously reduce the number of calls to your comparator function.

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And you might consider whether a std::unordered_set might be sufficient? I.e. whether you need to list the data in sorted order. Or if the sorting is just the internal stuff of std::set element insertion.

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Finally, for other readers (the OP has made clear that he's aware of this), remember to MEASURE.