commonMain.ru.casperix.math.random.XorWowRandom.kt Maven / Gradle / Ivy

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package ru.casperix.math.random

import kotlinx.serialization.Serializable
import kotlin.random.Random

/**
 * 	Say thanks, that kotlin author make this class internal
 */
@Serializable
data class XorWowRandom (
		private var x: Int,
		private var y: Int,
		private var z: Int,
		private var w: Int,
		private var v: Int,
		private var addend: Int
) : Random() {

	constructor(seed1: Int, seed2: Int) :
			this(seed1, seed2, 0, 0, seed1.inv(), (seed1 shl 10) xor (seed2 ushr 4))

	init {
		require((x or y or z or w or v) != 0) { "Initial state must have at least one non-zero element." }

		// some trivial seeds can produce several values with zeroes in upper bits, so we discard first 64
		repeat(64) { nextInt() }
	}

	override fun nextInt(): Int {
		// Equivalent to the xorxow algorithm
		// From Marsaglia, G. 2003. Xorshift RNGs. J. Statis. Soft. 8, 14, p. 5
		var t = x
		t = t xor (t ushr 2)
		x = y
		y = z
		z = w
		val v0 = v
		w = v0
		t = (t xor (t shl 1)) xor v0 xor (v0 shl 4)
		v = t
		addend += 362437
		return t + addend
	}

	override fun nextBits(bitCount: Int): Int =
			nextInt().takeUpperBits(bitCount)

	internal fun Int.takeUpperBits(bitCount: Int): Int =
		this.ushr(32 - bitCount) and (-bitCount).shr(31)
}