/*
* 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.util;
import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.lang.reflect.Method;
import java.math.BigDecimal;
import java.security.SecureRandom;
import java.util.Random;
import org.h2.message.DbException;
/**
* This is a utility class with mathematical helper functions.
*/
public class MathUtils {
/**
* The secure random object.
*/
static SecureRandom cachedSecureRandom;
/**
* True if the secure random object is seeded.
*/
static volatile boolean seeded;
private static final Random RANDOM = new Random();
/**
* The maximum scale of a BigDecimal value.
*/
private static final int BIG_DECIMAL_SCALE_MAX = 100000;
private MathUtils() {
// utility class
}
private static synchronized SecureRandom getSecureRandom() {
if (cachedSecureRandom != null) {
return cachedSecureRandom;
}
// Workaround for SecureRandom problem as described in
// http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6202721
// Can not do that in a static initializer block, because
// threads are not started until after the initializer block exits
try {
cachedSecureRandom = SecureRandom.getInstance("SHA1PRNG");
// On some systems, secureRandom.generateSeed() is very slow.
// In this case it is initialized using our own seed implementation
// and afterwards (in the thread) using the regular algorithm.
Runnable runnable = new Runnable() {
public void run() {
try {
SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
byte[] seed = sr.generateSeed(20);
synchronized (cachedSecureRandom) {
cachedSecureRandom.setSeed(seed);
seeded = true;
}
} catch (Exception e) {
// NoSuchAlgorithmException
warn("SecureRandom", e);
}
}
};
try {
Thread t = new Thread(runnable, "Generate Seed");
// let the process terminate even if generating the seed is really slow
t.setDaemon(true);
t.start();
Thread.yield();
try {
// normally, generateSeed takes less than 200 ms
t.join(400);
} catch (InterruptedException e) {
warn("InterruptedException", e);
}
if (!seeded) {
byte[] seed = generateAlternativeSeed();
// this never reduces randomness
synchronized (cachedSecureRandom) {
cachedSecureRandom.setSeed(seed);
}
}
} catch (SecurityException e) {
// workaround for the Google App Engine: don't use a thread
runnable.run();
generateAlternativeSeed();
}
} catch (Exception e) {
// NoSuchAlgorithmException
warn("SecureRandom", e);
cachedSecureRandom = new SecureRandom();
}
return cachedSecureRandom;
}
private static byte[] generateAlternativeSeed() {
try {
ByteArrayOutputStream bout = new ByteArrayOutputStream();
DataOutputStream out = new DataOutputStream(bout);
// milliseconds
out.writeLong(System.currentTimeMillis());
// nanoseconds if available
try {
Method m = System.class.getMethod("nanoTime");
if (m != null) {
Object o = m.invoke(null);
out.writeUTF(o.toString());
}
} catch (Exception e) {
// nanoTime not found, this is ok (only exists for JDK 1.5 and higher)
out.writeUTF(e.toString());
}
// memory
out.writeInt(new Object().hashCode());
Runtime runtime = Runtime.getRuntime();
out.writeLong(runtime.freeMemory());
out.writeLong(runtime.maxMemory());
out.writeLong(runtime.totalMemory());
// environment
try {
String s = System.getProperties().toString();
// can't use writeUTF, as the string
// might be larger than 64 KB
out.writeInt(s.length());
out.write(s.getBytes("UTF-8"));
} catch (Exception e) {
warn("generateAlternativeSeed", e);
}
// host name and ip addresses (if any)
try {
// workaround for the Google App Engine: don't use InetAddress
Class<?> inetAddressClass = Class.forName("java.net.InetAddress");
Object localHost = inetAddressClass.getMethod("getLocalHost").invoke(null);
String hostName = inetAddressClass.getMethod("getHostName").invoke(localHost).toString();
out.writeUTF(hostName);
Object[] list = (Object[]) inetAddressClass.getMethod("getAllByName", String.class).invoke(null, hostName);
Method getAddress = inetAddressClass.getMethod("getAddress");
for (Object o : list) {
out.write((byte[]) getAddress.invoke(o));
}
} catch (Throwable e) {
// on some system, InetAddress is not supported
// on some system, InetAddress.getLocalHost() doesn't work
// for some reason (incorrect configuration)
}
// timing (a second thread is already running usually)
for (int j = 0; j < 16; j++) {
int i = 0;
long end = System.currentTimeMillis();
while (end == System.currentTimeMillis()) {
i++;
}
out.writeInt(i);
}
out.close();
return bout.toByteArray();
} catch (IOException e) {
warn("generateAlternativeSeed", e);
return new byte[1];
}
}
/**
* Print a message to system output if there was a problem initializing the
* random number generator.
*
* @param s the message to print
* @param t the stack trace
*/
static void warn(String s, Throwable t) {
// not a fatal problem, but maybe reduced security
System.out.println("Warning: " + s);
if (t != null) {
t.printStackTrace();
}
}
/**
* Round the value up to the next block size. The block size must be a power
* of two. As an example, using the block size of 8, the following rounding
* operations are done: 0 stays 0; values 1..8 results in 8, 9..16 results
* in 16, and so on.
*
* @param x the value to be rounded
* @param blockSizePowerOf2 the block size
* @return the rounded value
*/
public static int roundUpInt(int x, int blockSizePowerOf2) {
return (x + blockSizePowerOf2 - 1) & (-blockSizePowerOf2);
}
/**
* Round the value up to the next block size. The block size must be a power
* of two. As an example, using the block size of 8, the following rounding
* operations are done: 0 stays 0; values 1..8 results in 8, 9..16 results
* in 16, and so on.
*
* @param x the value to be rounded
* @param blockSizePowerOf2 the block size
* @return the rounded value
*/
public static long roundUpLong(long x, long blockSizePowerOf2) {
return (x + blockSizePowerOf2 - 1) & (-blockSizePowerOf2);
}
/**
* Get the value that is equal or higher than this value, and that is a
* power of two.
*
* @param x the original value
* @return the next power of two value
*/
public static int nextPowerOf2(int x) {
long i = 1;
while (i < x && i < (Integer.MAX_VALUE / 2)) {
i += i;
}
return (int) i;
}
/**
* Set the scale of a BigDecimal value.
*
* @param bd the BigDecimal value
* @param scale the new scale
* @return the scaled value
*/
public static BigDecimal setScale(BigDecimal bd, int scale) {
if (scale > BIG_DECIMAL_SCALE_MAX || scale < -BIG_DECIMAL_SCALE_MAX) {
throw DbException.getInvalidValueException("scale", scale);
}
return bd.setScale(scale, BigDecimal.ROUND_HALF_UP);
}
/**
* Convert a long value to an int value. Values larger than the biggest int
* value is converted to the biggest int value, and values smaller than the
* smallest int value are converted to the smallest int value.
*
* @param l the value to convert
* @return the converted int value
*/
public static int convertLongToInt(long l) {
if (l <= Integer.MIN_VALUE) {
return Integer.MIN_VALUE;
} else if (l >= Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
} else {
return (int) l;
}
}
/**
* Compare two values. Returns -1 if the first value is smaller, 1 if bigger,
* and 0 if equal.
*
* @param a the first value
* @param b the second value
* @return the result
*/
public static int compareInt(int a, int b) {
return a == b ? 0 : a < b ? -1 : 1;
}
/**
* Compare two values. Returns -1 if the first value is smaller, 1 if bigger,
* and 0 if equal.
*
* @param a the first value
* @param b the second value
* @return the result
*/
public static int compareLong(long a, long b) {
return a == b ? 0 : a < b ? -1 : 1;
}
/**
* Get a cryptographically secure pseudo random long value.
*
* @return the random long value
*/
public static long secureRandomLong() {
SecureRandom sr = getSecureRandom();
synchronized (sr) {
return sr.nextLong();
}
}
/**
* Get a number of pseudo random bytes.
*
* @param bytes the target array
*/
public static void randomBytes(byte[] bytes) {
RANDOM.nextBytes(bytes);
}
/**
* Get a number of cryptographically secure pseudo random bytes.
*
* @param len the number of bytes
* @return the random bytes
*/
public static byte[] secureRandomBytes(int len) {
if (len <= 0) {
len = 1;
}
byte[] buff = new byte[len];
SecureRandom sr = getSecureRandom();
synchronized (sr) {
sr.nextBytes(buff);
}
return buff;
}
/**
* Get a pseudo random int value between 0 (including and the given value
* (excluding). The value is not cryptographically secure.
*
* @param lowerThan the value returned will be lower than this value
* @return the random long value
*/
public static int randomInt(int lowerThan) {
return RANDOM.nextInt(lowerThan);
}
/**
* Get a cryptographically secure pseudo random int value between 0
* (including and the given value (excluding).
*
* @param lowerThan the value returned will be lower than this value
* @return the random long value
*/
public static int secureRandomInt(int lowerThan) {
SecureRandom sr = getSecureRandom();
synchronized (sr) {
return sr.nextInt(lowerThan);
}
}
}