/*
* Copyright 2004-2011 H2 Group. Multiple-Licensed under the H2 License,
* Version 1.0, and under the Eclipse Public License, Version 1.0
* (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.test.unit;
import java.math.BigInteger;
import java.util.Random;
import org.h2.test.TestBase;
import org.h2.test.utils.AssertThrows;
import org.h2.util.MathUtils;
/**
* Tests math utility methods.
*/
public class TestMathUtils extends TestBase {
/**
* Run just this test.
*
* @param a ignored
*/
public static void main(String... a) throws Exception {
TestBase.createCaller().init().test();
}
public void test() {
testReverse();
testFactorial();
}
private void testReverse() {
assertEquals(Integer.reverse(0), MathUtils.reverseInt(0));
assertEquals(Integer.reverse(Integer.MAX_VALUE), MathUtils.reverseInt(Integer.MAX_VALUE));
assertEquals(Integer.reverse(Integer.MIN_VALUE), MathUtils.reverseInt(Integer.MIN_VALUE));
assertEquals(Long.reverse(0), MathUtils.reverseLong(0L));
assertEquals(Long.reverse(Long.MAX_VALUE), MathUtils.reverseLong(Long.MAX_VALUE));
assertEquals(Long.reverse(Long.MIN_VALUE), MathUtils.reverseLong(Long.MIN_VALUE));
for (int i = Integer.MIN_VALUE; i < 0; i += 1019) {
int x = MathUtils.reverseInt(i);
assertEquals(Integer.reverse(i), x);
}
for (int i = 0; i > 0; i += 1019) {
int x = MathUtils.reverseInt(i);
assertEquals(Integer.reverse(i), x);
}
for (long i = Long.MIN_VALUE; i < 0; i += 1018764321251L) {
long x = MathUtils.reverseLong(i);
assertEquals(Long.reverse(i), x);
}
for (long i = 0; i > 0; i += 1018764321251L) {
long x = MathUtils.reverseLong(i);
assertEquals(Long.reverse(i), x);
}
Random random = new Random(10);
for (int i = 0; i < 1000000; i++) {
long x = random.nextLong();
long r = MathUtils.reverseLong(x);
assertEquals(Long.reverse(x), r);
int y = random.nextInt();
int s = MathUtils.reverseInt(y);
assertEquals(Integer.reverse(y), s);
}
}
private void testFactorial() {
new AssertThrows(IllegalArgumentException.class) { public void test() {
factorial(-1);
}};
assertEquals("1", factorial(0).toString());
assertEquals("1", factorial(1).toString());
assertEquals("2", factorial(2).toString());
assertEquals("6", factorial(3).toString());
assertEquals("3628800", factorial(10).toString());
assertEquals("2432902008176640000", factorial(20).toString());
}
/**
* Calculate the factorial (n!) of a number.
* This implementation uses a naive multiplication loop, and
* is very slow for large n.
* For n = 1000, it takes about 10 ms.
* For n = 8000, it takes about 800 ms.
*
* @param n the number
* @return the factorial of n
*/
public static BigInteger factorial(int n) {
if (n < 0) {
throw new IllegalArgumentException(n + "<0");
} else if (n < 2) {
return BigInteger.ONE;
}
BigInteger x = new BigInteger("" + n);
BigInteger result = x;
for (int i = n - 1; i >= 2; i--) {
x = x.subtract(BigInteger.ONE);
result = result.multiply(x);
}
return result;
}
}