qsort strikes me as a bit of a crappy benchmark because of the type erasure. Your compiler likely isn't inlining or applying vectorisation. Vectorisation would likely benefit 32bit floats on a 64bit platform more than doubles.
I'd tested a number of sort algorithms (bubble, insertion, quick, merge, counting), so also testing the sort function from stdlib seemed like a logical continuation.
It was done rather quickly, so there wasn't time to properly investigate, merely look at the numbers and go "that's strange".
