Few remarks: -mtune is redundant with march=native turned on; -use -Ofast instead O3/ffast-math it turns some more options as well (although theoretically it

Few remarks: -mtune is redundant with march=native turned on; -use -Ofast instead O3/ffast-math it turns some more options as well (although theoretically it might behave in non-standard way with float computations, you need to test this, it wasn't ever a problem for me) -add -flto it often helps significantly -it probably won't matter for simple program but you may try compiling with: -Ofast -march=native -flto -fprofile-generate; then run the program (it will generate .gcda files) and then recompile with the same options and -fprofile-use; EDIT: Some quick tests shows that all the options I mentioned help (MinGW, gcc 4.8.1). Original time on one thread was 3.670s, Ofast and -flto takes it to ~3.630s and adding PGO moves it to 3.46s (there is some variance with all of those) - whooping 5-6% improvement overall :)