testnative: fix when building with -DSDL_LIBC=OFF

[madebr]

SDL_rand returns unsigned integers,
so SDL_rand() % (MAX_SPEED * 2 + 1)) - MAX_SPEED (MAX_SPEED = 1) can result in 2**32-1.

I also included a bonus fix for testnative.c that failed to link on Windows when built with -DSDL_LIBC=OFF.
Including build_config/SDL_build_config.h directly was simpler then copying the testevdev workaround to include SDL_internal.h.

Description

Existing Issue(s)

[JKaniarz]

See my comments on pr #10063

SDL_rand() % n is a common, but bad, way of getting a random number < n. That's why I added SDL_rand_n() in my PR.

I know I'm deviating from std::rand() by returning a Uint32. I did update the docs to say it returns 32 random bits (instead of a number) and suggest using SDL_rand_n(). Here are the pros/cons:

• Returning 31 random bits is the norm, and predicability is good.
• Returning 31 random bits makes doing things right more complicated and people will default to the bad SDL_rand()%n .

There's an open question on the PR about if SDL_rand_n() should use Sint32 even though negative numbers don't quite work right.

[slouken]

SDL_rand_n() should probably take and return Sint32, but document that the valid range of n is [0...SDL_MAX_SINT32], otherwise you'll run into problems mixing SDL_rand_n() with signed arithmetic.

[slouken]

We should probably have SDL_RAND_MAX, for consistency. :)

[JKaniarz]

SDL_rand_n() should probably take and return Sint32, but document that the valid range of n is [0...SDL_MAX_SINT32], otherwise you'll run into problems mixing SDL_rand_n() with signed arithmetic.

Will do.

[slouken]

I agree that SDL_rand() should return 32-bits, so we have the full 32-bits of values for _float(), etc... actually, float can't represent the full range of 32-bit values, maybe using 31 bits would be fine?

[JKaniarz]

What if we rename SDL_rand() to SDL_rand_bits(), and make SDL_rand() take an n parameter so nobody can accidentally use it like std::rand? And forget SDL_RAND_MAX because you manually provide the max to rand.

Edit: I really like the rand_bits() idea. But maybe we can keep the std::rand() interface for SDL_rand().
Edit Edit: But I really really want to stop people from doing SDL_rand() % n

[slouken]

Maybe we don't expose the rand() interface at all? We just have rand_n and rand_float?

[JKaniarz]

Maybe we don't expose the rand() interface at all? We just have rand_n and rand_float?

Yeah. If we're not going to implement std::rand() with all its warts, we probably shouldn't mimic its interface.

[JKaniarz]

Just submitted #10064

Deleted SDL_rand() to force users onto the correct functions.
SDL_rand_bits() is Uint32.
SDL_rand_n(n) is Sint32

[JKaniarz]

@madebr With the changes on #10064, I think commit 61a58a8 is no longer necessary (and will also cause a merge conflict). Does the PR address your concern?

[madebr]

@madebr With the changes on #10064, I think commit 61a58a8 is no longer necessary (and will also cause a merge conflict). Does the PR address your concern?

Yes! I just tried your pr and testnative behaves fine.
Thanks for the improvements!

(src/dynapi/SDL_dynapi.sym still contains SDL_rand_r and is slightly unsorted around SDL_rand)