pcg-based rand32() and rand64()

rand.h

// pcg-based rand32() and rand64()
#include <stdint.h>

struct pcg32_random_t
{
    uint64_t state;
};

static const uint64_t inc = 997;
static struct pcg32_random_t rndState = {99991};

static uint32_t pcg32_random_r(struct pcg32_random_t* rng)
{
    uint64_t oldstate = rng->state;
    rng->state = oldstate * 6364136223846793005ULL + (inc | 1);
    uint32_t xorshifted = (uint32_t)(((oldstate >> 18u) ^ oldstate) >> 27u);
    uint32_t rot = (uint32_t)(oldstate >> 59u);
    return (xorshifted >> rot) | (xorshifted << ((-(int32_t)(rot)) & 31));
}

static uint32_t rand32()
{
    return pcg32_random_r(&rndState);
}

static uint64_t rand64()
{
    return pcg32_random_r(&rndState) | ((1ULL * pcg32_random_r(&rndState)) << 32);
}