Simple random number generator.

rng.c

#include <stdlib.h>
#include <stdint.h>
#include "rng.h"

static uint32_t rng_current_seed = 0;

rng *
rng_create(uint32_t seed) {
	rng *r = malloc(sizeof(r));
	r->seed = seed;
	r->gens = 0;
	return r;
}

void
rng_free(rng *r) {
	if (r)
		free(r);
}

uint32_t 
rng_next(rng *r, uint32_t min, uint32_t max) {
	
	// reseed to the current generation
	if (rng_current_seed != r->seed) {
	
		rng_current_seed = r->seed;
		srand(rng_current_seed);

		uint32_t n = 0;
		while (n<r->gens) {
			rand();
			n++;
		}
	}

	r->gens++;
	return rand() % (max - min) + min; 
}

uint32_t
rng_next0(rng *r, uint32_t max) {
	return rng_next(r, 0, max);
}

rng.h

#include <stdint.h>

typedef struct rng_t rng;
struct rng_t {
	uint32_t seed;
	uint32_t gens;
};

rng *
rng_create(uint32_t seed);

void
rng_free(rng *r);

uint32_t 
rng_next(rng *r, uint32_t min, uint32_t max);

uint32_t
rng_next0(rng *r, uint32_t max);