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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.collections;
import com.yahoo.text.Utf8;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
/**
* Convenience class for hashing a String with MD5, and either returning
* an int with the 4 LSBytes, or the whole 12-byte MD5 hash.
* <p>
* Note that instantiating this class can be expensive, so re-using instances
* is a good idea.
* <p>
* This class is not thread safe.
*
* @author Einar M R Rosenvinge
*/
public class MD5 {
public static final ThreadLocal<MessageDigest> md5 = new MD5Factory();
private static class MD5Factory extends ThreadLocal<MessageDigest> {
@Override
protected MessageDigest initialValue() {
return createMD5();
}
}
private static MessageDigest createMD5() {
try {
return MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
}
final private MessageDigest digester;
public MD5() {
try {
digester = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
throw new AssertionError("MD5 algorithm not found.");
}
}
public int hash(String s) {
byte[] md5 = digester.digest(Utf8.toBytes(s));
int hash = 0;
assert (md5.length == 16);
//produce an int by using only the 32 lsb:
int byte1 = (((int) md5[12]) << 24) & 0xFF000000;
int byte2 = (((int) md5[13]) << 16) & 0x00FF0000;
int byte3 = (((int) md5[14]) << 8) & 0x0000FF00;
int byte4 = (((int) md5[15])) & 0x000000FF;
hash |= byte1;
hash |= byte2;
hash |= byte3;
hash |= byte4;
return hash;
}
public byte[] hashFull(String s) {
return digester.digest(Utf8.toBytes(s));
}
}
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