package sim

// Rng_State is owned by Sim_State so all gameplay randomness is seed-driven and
// replayable. No gameplay code should use global/random platform state directly.
Rng_State :: struct {
	value: u64,
}

// Initialize the deterministic random stream from the run seed. A zero seed is
// remapped so the generator always has a useful non-zero state to advance from.
rng_from_seed :: proc(seed: u64) -> Rng_State {
	state := seed
	if state == 0 {
		state = 0x9E3779B97F4A7C15
	}
	return Rng_State{value = state}
}

// Advance and return the next deterministic random value. SplitMix64 is small,
// fast, and stable enough for this substrate; if later gameplay needs separate
// random domains, those should become explicit named streams in Sim_State.
rng_next_u64 :: proc(rng: ^Rng_State) -> u64 {
	rng.value += 0x9E3779B97F4A7C15
	z := rng.value
	z = (z ~ (z >> 30)) * 0xBF58476D1CE4E5B9
	z = (z ~ (z >> 27)) * 0x94D049BB133111EB
	return z ~ (z >> 31)
}