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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.bits;

import static org.junit.Assert.assertEquals;
import it.unimi.dsi.util.SplitMix64RandomGenerator;

import org.junit.Test;

/*
 * DSI utilities
 *
 * Copyright (C) 2010-2020 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 .
 *
 */

public class FastTest {

	@Test
	public void testCeilLog2() {
		for(int i = 1; i < 1000; i++) assertEquals((int)Math.ceil(Math.log(i) / Math.log(2)), Fast.ceilLog2(i));
	}

	@Test
	public void testLength() {
		assertEquals(1, Fast.length(0));
		assertEquals(1, Fast.length(0L));
		for(int i = 1; i < 100; i++) assertEquals(Fast.mostSignificantBit(i) + 1, Fast.length(i));
		for(long i = 1; i < 100; i++) assertEquals(Fast.mostSignificantBit(i) + 1, Fast.length(i));
	}

	@Test
	public void testMostSignificantBitInt() {
		assertEquals(-1, Fast.mostSignificantBit(0));
		for(int i = 0; i < 32; i++) {
			assertEquals(i, Fast.mostSignificantBit(1L << i));
			assertEquals(i, Fast.mostSignificantBit(1L << i | 1));
			assertEquals(i, Fast.mostSignificantBit(1L << i));
			assertEquals(i, Fast.mostSignificantBit(1L << i | 1));
		}
	}

	@Test
	public void testMostSignificantBitLong() {
		assertEquals(-1, Fast.mostSignificantBit(0));
		for(int i = 0; i < 64; i++) {
			assertEquals(i, Fast.mostSignificantBit(1L << i));
			assertEquals(i, Fast.mostSignificantBit(1L << i | 1));
			assertEquals(i, Fast.mostSignificantBit(1L << i));
			assertEquals(i, Fast.mostSignificantBit(1L << i | 1));
		}
	}


	@Test
	public void testSelect2() {
		assertEquals(0, Fast.select(1, 0));
		for(int i = 0; i < 64; i++) assertEquals(i, Fast.select(0xFFFFFFFFFFFFFFFFL, i));
		for(int i = 1; i < 32; i++) assertEquals(2 * i + 1, Fast.select(0xAAAAAAAAAAAAAAAAL, i));
		SplitMix64RandomGenerator r = new SplitMix64RandomGenerator(0);
		for(int i = 100000; i-- != 0;) {
			final long x = r.nextLong();
			final int count = Long.bitCount(x);
			for(int rank = count; rank-- != 0;) assertEquals(Fast.select(x, rank), Fast.select(x, rank));
		}
	}



	@Test
	public void testInt2Nat() {
		assertEquals(Integer.MAX_VALUE, Fast.int2nat(Integer.MIN_VALUE / 2));
		assertEquals(Integer.MAX_VALUE - 2, Fast.int2nat(Integer.MIN_VALUE / 2 + 1));
		assertEquals(Integer.MAX_VALUE - 1, Fast.int2nat(Integer.MAX_VALUE / 2));

		for(int i = 0; i < 16; i++) assertEquals(2*i, Fast.int2nat(i));
		for(int i = -16; i < 0; i++) assertEquals(-2*i-1, Fast.int2nat(i));

		assertEquals(Long.MAX_VALUE, Fast.int2nat(Long.MIN_VALUE / 2));
		assertEquals(Long.MAX_VALUE - 2, Fast.int2nat(Long.MIN_VALUE / 2 + 1));
		assertEquals(Long.MAX_VALUE - 1, Fast.int2nat(Long.MAX_VALUE / 2));

		for(int i = 0; i < 16; i++) assertEquals(2L*i, Fast.int2nat(i));
		for(int i = -16; i < 0; i++) assertEquals(-2L*i-1, Fast.int2nat(i));
	}

	@Test
	public void testNat2Int() {
		assertEquals(Integer.MIN_VALUE / 2, Fast.nat2int(Integer.MAX_VALUE));
		assertEquals(Integer.MIN_VALUE / 2 + 1, Fast.nat2int(Integer.MAX_VALUE - 2));
		assertEquals(Integer.MAX_VALUE / 2, Fast.nat2int(Integer.MAX_VALUE - 1));

		for(int i = 0; i < 16; i++) assertEquals(i, Fast.nat2int(2*i));
		for(int i = -16; i < 0; i++) assertEquals(i, Fast.nat2int(-2*i-1));

		assertEquals(Long.MIN_VALUE / 2 + 1, Fast.nat2int(Long.MAX_VALUE - 2));
		assertEquals(Long.MIN_VALUE / 2, Fast.nat2int(Long.MAX_VALUE));
		assertEquals(Long.MAX_VALUE / 2, Fast.nat2int(Long.MAX_VALUE - 1));

		for(int i = 0; i < 16; i++) assertEquals(i, Fast.nat2int(2L*i));
		for(int i = -16; i < 0; i++) assertEquals(i, Fast.nat2int(-2L*i-1));

	}
}