org.h2.util.MathUtils Maven / Gradle / Ivy
/*
* Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://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.nio.charset.StandardCharsets;
import java.security.SecureRandom;
import java.util.concurrent.ThreadLocalRandom;
/**
* 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 MathUtils() {
// utility class
}
/**
* 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);
}
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() {
@Override
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;
}
/**
* Generate a seed value, using as much unpredictable data as possible.
*
* @return the seed
*/
public static byte[] generateAlternativeSeed() {
try {
ByteArrayOutputStream bout = new ByteArrayOutputStream();
DataOutputStream out = new DataOutputStream(bout);
// milliseconds and nanoseconds
out.writeLong(System.currentTimeMillis());
out.writeLong(System.nanoTime());
// 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(StandardCharsets.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();
}
}
/**
* Get the value that is equal to or higher than this value, and that is a
* power of two.
*
* @param x the original value
* @return the next power of two value
* @throws IllegalArgumentException if x < 0 or x > 0x40000000
*/
public static int nextPowerOf2(int x) throws IllegalArgumentException {
if (x == 0) {
return 1;
} else if (x < 0 || x > 0x4000_0000 ) {
throw new IllegalArgumentException("Argument out of range"
+ " [0x0-0x40000000]. Argument was: " + x);
}
x--;
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return ++x;
}
/**
* 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;
}
}
/**
* Get a cryptographically secure pseudo random long value.
*
* @return the random long value
*/
public static long secureRandomLong() {
return getSecureRandom().nextLong();
}
/**
* Get a number of pseudo random bytes.
*
* @param bytes the target array
*/
public static void randomBytes(byte[] bytes) {
ThreadLocalRandom.current().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];
getSecureRandom().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 ThreadLocalRandom.current().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) {
return getSecureRandom().nextInt(lowerThan);
}
}