#include <stdlib.h>

/**
 * Raw memory type used for representing the maximum random size of a value.
 */
typedef long unsigned Seed;

/**
 * State machine for an instance of XOR shift-based pseudo-random number generation.
 */
typedef struct XorShifter {
	/**
	 * Initial seed state iniailized when creating the pseudo-random number generator, set by
	 * either manually arranging the memory or by calling [CreateXorShifter(seed_t const)]. Every
	 * time a new random number is generated, usually by calling
	 * [GetXorShifterValue(XorShifter* const, long const, long const)], this value will be mutated
	 * with the new iteration value.
	 */
	Seed seed;
} XorShifter;

/**
 * Creates a [XorShifter] with the given `seed` as initial entropy. Note that like all pseudo-
 * random number generators, the initial seed makes all sequential operations deterministic to the
 * value. I.e. running the same program twice with the same seed will yield the same results. To
 * get more entropic values either pass in the current UNIX timestamp value of the device or poll
 * the device's system-dependant entropy device for a new seed each run.
 */
XorShifter CreateXorShifter(Seed const seed) {
	return (XorShifter){seed};
}

/**
 * Returns the next pseudo-random iteration in the `xorShifter`'s seeded sequence, reduced down a
 * range between `min` and `max`, provided the `xorShifter`'s seed is greater than `0`.
 */
long const GetXorShifterValue(XorShifter* const xorShifter, long const min, long const max) {
	if (xorShifter->seed) {
		Seed value = xorShifter->seed;
		value ^= value << 13;
		value ^= value >> 17;
		value ^= value << 5;

		return labs((long)(xorShifter->seed = value)) % (labs(max - min) + 1) + min;
	}

	return 0;
}