fwiw, I took a stab at replacing a bunch of => with . and ran it:
time ./crb-vec-omp
real 0m0.764s
which is more than twice as fast as the rust example,
but it didn't create the right output...
if you get bored would you mind taking a stab at adding parallel and modifying crb-vec.c https://github.com/niofis/raybench , I definitely think you might be on to something here.