$ cc -o mb mb.c -g3 -O0 -lm
$ time ./mb >/dev/null

real	0m4.135s
user	0m4.116s
sys	0m0.006s
$ cc -o mb mb.c -g3 -O0 -fopenmp -lm
$ time ./mb >/dev/null

real	0m1.045s
user	0m7.184s
sys	0m0.061s
$ cc -o mb mb.c -g3 -O1 -lm
$ time ./mb >/dev/null

real	0m3.367s
user	0m3.351s
sys	0m0.008s
$ cc -o mb mb.c -g3 -O1 -fopenmp -lm
$ time ./mb >/dev/null

real	0m0.760s
user	0m5.165s
sys	0m0.005s
$ cc -o mb mb.c -g3 -O2 -lm
$ time ./mb >/dev/null

real	0m3.183s
user	0m3.164s
sys	0m0.008s
$ cc -o mb mb.c -g3 -O2 -fopenmp -lm
$ time ./mb >/dev/null

real	0m0.757s
user	0m4.876s
sys	0m0.004s
$ cc -o mb mb.c -g3 -O3 -lm
$ time ./mb >/dev/null

real	0m3.204s
user	0m3.186s
sys	0m0.007s
$ cc -o mb mb.c -g3 -O3 -fopenmp -lm
$ time ./mb >/dev/null

real	0m0.762s
user	0m4.905s
sys	0m0.002s
$ cc -o mb mb.c -g3 -Ofast -lm
$ time ./mb >/dev/null

real	0m1.521s
user	0m1.507s
sys	0m0.010s
$ cc -o mb mb.c -g3 -Ofast -fopenmp -lm
$ time ./mb >/dev/null

real	0m0.287s
user	0m1.933s
sys	0m0.004s
$ cc --version
cc (GCC) 14.0.1 20240411 (Red Hat 14.0.1-0)
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$