My thought about hand rolling is that any loop is hand-rolled if I tell the compiler how to do things (ie not declarative). Writing out a for loop with an s+=*p

My thought about hand rolling is that any loop is hand-rolled if I tell the compiler how to do things (ie not declarative). Writing out a for loop with an s+=*p++ for summing the elements in a vector is hand rolling a “reduce”. You can add all the tricks you want like changing the stride, doing simd, prefetching, but I’ve learned to let the compiler or the math/data library do its job. For small data (MB) the compiler or library can parallelize things nicely. Bigger data (TB+) can be chewed threw by using MPI aware libraries that optimize and schedule and everything. Database work is already declarative because SQL is just so awesome. C# and java now handle fusion and streams more nicely and c++ can in-line and r-value a lot of overhead away.