Minestom/src/main/java/net/minestom/server/utils/Utils.java

package net.minestom.server.utils;

import org.jetbrains.annotations.ApiStatus;
import org.jetbrains.annotations.NotNull;

import java.nio.ByteBuffer;
import java.util.UUID;

@ApiStatus.Internal
public final class Utils {

    private Utils() {
    }

    public static int getVarIntSize(int input) {
        return (input & 0xFFFFFF80) == 0
                ? 1 : (input & 0xFFFFC000) == 0
                ? 2 : (input & 0xFFE00000) == 0
                ? 3 : (input & 0xF0000000) == 0
                ? 4 : 5;
    }

    public static void writeVarInt(ByteBuffer buf, int value) {
        if ((value & (0xFFFFFFFF << 7)) == 0) {
            buf.put((byte) value);
        } else if ((value & (0xFFFFFFFF << 14)) == 0) {
            buf.putShort((short) ((value & 0x7F | 0x80) << 8 | (value >>> 7)));
        } else if ((value & (0xFFFFFFFF << 21)) == 0) {
            buf.put((byte) (value & 0x7F | 0x80));
            buf.put((byte) ((value >>> 7) & 0x7F | 0x80));
            buf.put((byte) (value >>> 14));
        } else if ((value & (0xFFFFFFFF << 28)) == 0) {
            buf.putInt((value & 0x7F | 0x80) << 24 | (((value >>> 7) & 0x7F | 0x80) << 16)
                    | ((value >>> 14) & 0x7F | 0x80) << 8 | (value >>> 21));
        } else {
            buf.putInt((value & 0x7F | 0x80) << 24 | ((value >>> 7) & 0x7F | 0x80) << 16
                    | ((value >>> 14) & 0x7F | 0x80) << 8 | ((value >>> 21) & 0x7F | 0x80));
            buf.put((byte) (value >>> 28));
        }
    }

    public static void writeVarIntHeader(@NotNull ByteBuffer buffer, int startIndex, int value) {
        buffer.put(startIndex, (byte) (value & 0x7F | 0x80));
        buffer.put(startIndex + 1, (byte) ((value >>> 7) & 0x7F | 0x80));
        buffer.put(startIndex + 2, (byte) (value >>> 14));
    }

    public static int readVarInt(ByteBuffer buf) {
        // https://github.com/jvm-profiling-tools/async-profiler/blob/a38a375dc62b31a8109f3af97366a307abb0fe6f/src/converter/one/jfr/JfrReader.java#L393
        int result = 0;
        for (int shift = 0; ; shift += 7) {
            byte b = buf.get();
            result |= (b & 0x7f) << shift;
            if (b >= 0) {
                return result;
            }
        }
    }
}