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The DSI utilities are a mishmash of classes accumulated during the last twenty years in projects developed at the DSI (Dipartimento di Scienze dell'Informazione, i.e., Information Sciences Department), now DI (Dipartimento di Informatica, i.e., Informatics Department), of the Universita` degli Studi di Milano.

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package it.unimi.dsi.util;

/*
 * DSI utilities
 *
 * Copyright (C) 2015-2020 Sebastiano Vigna
 *
 *  This library is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 3 of the License, or (at your option)
 *  any later version.
 *
 *  This library is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 *  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program; if not, see .
 *
 */


import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

import org.junit.Test;


public class SplitMix64RandomTest {
	private final static long seeds[] = { 0, 1, 1024, 0x5555555555555555L };

	@Test
	public void testNextFloat() {
		for (long seed : seeds) {
			SplitMix64Random splitMixRandom = new SplitMix64Random(seed);
			double avg = 0;
			for (int i = 1000000; i-- != 0;) {
				float d = splitMixRandom.nextFloat();
				assertTrue(d < 1);
				assertTrue(d >= 0);
				avg += d;
			}

			assertEquals(500000, avg, 1000);
		}
	}

	@Test
	public void testNextDouble() {
		for (long seed : seeds) {
			SplitMix64Random splitMixRandom = new SplitMix64Random(seed);
			double avg = 0;
			for (int i = 1000000; i-- != 0;) {
				double d = splitMixRandom.nextDouble();
				assertTrue(d < 1);
				assertTrue(d >= 0);
				avg += d;
			}

			assertEquals(500000, avg, 500);
		}
	}

	@Test
	public void testNextInt() {
		for (long seed : seeds) {
			SplitMix64Random splitMixRandom = new SplitMix64Random(seed);
			double avg = 0;
			for (int i = 100000000; i-- != 0;) {
				int d = splitMixRandom.nextInt(101);
				assertTrue(d <= 100);
				assertTrue(d >= 0);
				avg += d;
			}

			assertEquals(5000000000L, avg, 1000000);
		}
	}

	@Test
	public void testNextInt2() {
		for (long seed : seeds) {
			SplitMix64Random splitMixRandom = new SplitMix64Random(seed);
			final int[] count = new int[32];
			long change = 0;
			int prev = 0;
			for (int i = 1000000; i-- != 0;) {
				int d = splitMixRandom.nextInt();
				change += Long.bitCount(d ^ prev);
				for (int b = 32; b-- != 0;)
					if ((d & (1 << b)) != 0) count[b]++;
				prev = d;
			}

			assertEquals(32 * 1000000L, change, 23000);
			for (int b = 32; b-- != 0;) assertEquals(500000, count[b], 1500);
		}
	}

	@Test
	public void testNextLong() {
		for (long seed : seeds) {
			SplitMix64Random splitMixRandom = new SplitMix64Random(seed);
			final int[] count = new int[64];
			long change = 0;
			long prev = 0;
			for (int i = 1000000; i-- != 0;) {
				long d = splitMixRandom.nextLong();
				change += Long.bitCount(d ^ prev);
				for (int b = 64; b-- != 0;)
					if ((d & (1L << b)) != 0) count[b]++;
				prev = d;
			}

			assertEquals(32 * 1000000L, change, 4000);
			for (int b = 64; b-- != 0;) assertEquals(500000, count[b], 1500);
		}
	}
}