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If I have a large array of integers or floats, what is a good algorithm/
implementation for sorting (in C)?
It is a bit late in the game for an edit… but I am looking for correctness and speed.
For sorting arrays of numbers, consider a radix sort algorithm. When properly engineered, these sorts should provide better performance than GLIBC qsort().
The usort library contains type-specific implementations for all the major C numeric types.
https://github.com/setjmp/usort
The speed advantage of radix sort over GLIBC qsort is about 2.5x for double precision floating point numbers at N=1000000 on my 64 bit intel laptop. However, as N grows the advantage should be even greater since radix sort is a linear time algorithm requiring constant number of passes through the data.
For very small N, the same code dispatches to an introsort or insertion sort.