Mergesort would be a poor choice for qsort() due to the linear space complexity. With N bytes of RAM, you'd only be able to sort (a bit less than) N/2 bytes of data. An in-place algorithm is preferable.
Glibc is the only libc I'm aware of that implements mergesort. It still falls back to quicksort for large inputs though.
Glibc is the only libc I'm aware of that implements mergesort. It still falls back to quicksort for large inputs though.