How to generate a (correct) Minecraft-style hex digest. Tested.

_LICENSE

This software is licensed under the CC0 Public Domain Dedication.
See https://creativecommons.org/publicdomain/zero/1.0/ for more details.

BrokenHash.java

package com.unascribed.brokenhash;

import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import java.nio.charset.StandardCharsets;

/**
 * Generates a broken Minecraft-style twos-complement signed
 * hex digest. Tested and confirmed to match vanilla.
 */
public class BrokenHash {
	public static String hash(String str) {
		try {
			byte[] digest = digest(str, "SHA-1");
			return new BigInteger(digest).toString(16);
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException(e);
		}
	}

	private static byte[] digest(String str, String algorithm) throws NoSuchAlgorithmException {
		MessageDigest md = MessageDigest.getInstance(algorithm);
		byte[] strBytes = str.getBytes(StandardCharsets.UTF_8);
		return md.digest(strBytes);
	}
}

do u need the server id for this

Can you give the benchmark numbers? Did I miss them?

Thanks

Gist apparently doesn't notify me when comments are posted. 😠

@mcjp78 - No, the server ID is always blank in recent versions of Minecraft.

@deprilula28 - Sure; note that I've upgraded my hardware since I wrote this originally:

Generating workset... 200/2000
Warming up... Done
GCing... Done
Benchmarking Method #1... Done in 4.405 s (avg 88095.63ns per run)
GCing... Done
Benchmarking Method #2... Done in 2.172 s (avg 43447.664ns per run)

Both methods are very fast and there is no reason to use MethodTwo. I wrote it to learn how twos-complement and such works.

Also note that I have learned since I wrote this that the method I use to benchmark is fundamentally broken. I should have used an existing microbenchmark library, but I didn't, and as a result the test sucks and isn't really meaningful.

EDIT: I've removed the second method and the benchmark from the Gist.