[bjourne]

Have you tried passing everything by value? That is, instead of:

    bool hit_sphere(const struct sphere* sp, const struct ray* ray, struct hit* hit)

you write:

    static bool
    hit_sphere(struct sphere sp, struct ray ray, struct hit hit)

IME, clang is insanely good at optimizing pass by value calls.

[hackerpacker]

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.