rand32_timer: make it more random-like for tests to pass

#include <zephyr/random/rand32.h>

#include <zephyr/drivers/timer/system_timer.h>

#include <zephyr/kernel.h>

#include <zephyr/sys/atomic.h>

#include <zephyr/spinlock.h>

#include <string.h>

#if defined(__GNUC__)

/*

 * Symbols used to ensure a rapid series of calls to random number generator

 * return different values.

 */

static atomic_val_t _rand32_counter;

#define _RAND32_INC 1000000003U

static struct k_spinlock rand32_lock;

/**

 * @brief Get a 32 bit random number

 *

 * The non-random number generator returns values that are based off the

 * This pseudo-random number generator returns values that are based off the

 * target's clock counter, which means that successive calls will return

 * different values.

 *

 */

uint32_t z_impl_sys_rand32_get(void)

{

	return k_cycle_get_32() + atomic_add(&_rand32_counter, _RAND32_INC);

	static uint64_t state = 123456789UL;  /* initial seed value */

	k_spinlock_key_t key = k_spin_lock(&rand32_lock);

	state = state + k_cycle_get_32();

	state = state * 2862933555777941757ULL + 3037000493ULL;

	uint32_t val = (uint32_t)(state >> 32);

	k_spin_unlock(&rand32_lock, key);

	return val;

}

/**

 * @brief Fill destination buffer with random numbers

 *

 * The non-random number generator returns values that are based off the

 * The pseudo-random number generator returns values that are based off the

 * target's clock counter, which means that successive calls will return

 * different values.

 *