#include "rand.h"
#include "sys.h"
#include "memory.h"
#include "thread_local.h"

/* TODO: Use a value that gives good precision when dividing into range 0 -> 1 */
#define F64_RAND_MAX U64_MAX

/* ========================== *
 * Stateful prng
 * ========================== */

u64 rand_u64_from_state(struct rand_state *state)
{
    u64 seed = state->seed;
    if (seed == 0) {
        sys_true_rand(STRING_FROM_STRUCT(&seed));
        state->seed = seed;
    }
    return seed ^ rand_u64_from_seed(++state->counter);
}

f64 rand_f64_from_state(struct rand_state *state, f64 range_start, f64 range_end)
{
    return range_start + (range_end - range_start) * ((f64)(rand_u64_from_state(state) % F64_RAND_MAX) / (f64)F64_RAND_MAX);
}

/* ========================== *
 * Seeded prng
 * ========================== */

 /* Based on Jon Maiga's "mx3"
  * https://jonkagstrom.com/mx3/mx3_rev2.html
  */
u64 rand_u64_from_seed(u64 seed)
{
    seed = (seed ^ (seed >> 32)) * 0xbea225f9eb34556d;
    seed = (seed ^ (seed >> 29)) * 0xbea225f9eb34556d;
    seed = (seed ^ (seed >> 32)) * 0xbea225f9eb34556d;
    seed = (seed ^ (seed >> 29));
    return seed;
}

u64 rand_u64_from_seeds(u64 seed_a, u64 seed_b)
{
    return rand_u64_from_seed((seed_a * 3) + seed_b);
}

f64 rand_f64_from_seed(u64 seed, f64 range_start, f64 range_end)
{
    return range_start + (range_end - range_start) * ((f64)(rand_u64_from_seed(seed) % F64_RAND_MAX) / (f64)F64_RAND_MAX);
}