[zhangxp1998]

qsort has to invoke your comparison function repeatedly, which incurs a lot of overhead. Try C++'s std::sort

[zhangxp1998]

See https://gist.github.com/zhangxp1998/0e2fa30656c894017d183e0d... for a comparison of quadsort with C++'s std::sort. The compare functions are inlined.

[thedance]

Thanks for saving us the time. The punch line:

  Summarize: Slower than std::sort except on random tail.

Also a very important tidbit that std::sort is 10x faster than c's qsort for ordered inputs.

[alexchamberlain]

This feels a little unfair; the function is invoked the same number of times, but C++ has a mechanism for removing the overhead of calling a function (inlining).

[zhangxp1998]

I looked at disassembly of generated binary, sure, function calls inside quad sort were also inlined.