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 writeEmptyVarIntHeader(@NotNull ByteBuffer buffer) {
        final int index = buffer.position();
        buffer.position(index + 3); // Skip 3 bytes
        return index;
    }

    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;
            }
        }
    }

    public static long readVarLong(@NotNull ByteBuffer buf) {
        // https://github.com/jvm-profiling-tools/async-profiler/blob/a38a375dc62b31a8109f3af97366a307abb0fe6f/src/converter/one/jfr/JfrReader.java#L404
        long result = 0;
        for (int shift = 0; shift < 56; shift += 7) {
            byte b = buf.get();
            result |= (b & 0x7fL) << shift;
            if (b >= 0) {
                return result;
            }
        }
        return result | (buf.get() & 0xffL) << 56;
    }

    public static void writeVarLong(ByteBuffer buffer, long value) {
        do {
            byte temp = (byte) (value & 0b01111111);
            value >>>= 7;
            if (value != 0) {
                temp |= 0b10000000;
            }
            buffer.put(temp);
        } while (value != 0);
    }

    public static int[] uuidToIntArray(UUID uuid) {
        int[] array = new int[4];

        final long uuidMost = uuid.getMostSignificantBits();
        final long uuidLeast = uuid.getLeastSignificantBits();

        array[0] = (int) (uuidMost >> 32);
        array[1] = (int) uuidMost;

        array[2] = (int) (uuidLeast >> 32);
        array[3] = (int) uuidLeast;

        return array;
    }

    public static UUID intArrayToUuid(int[] array) {
        final long uuidMost = (long) array[0] << 32 | array[1] & 0xFFFFFFFFL;
        final long uuidLeast = (long) array[2] << 32 | array[3] & 0xFFFFFFFFL;

        return new UUID(uuidMost, uuidLeast);
    }

    private static final int[] MAGIC = {
            -1, -1, 0, Integer.MIN_VALUE, 0, 0, 1431655765, 1431655765, 0, Integer.MIN_VALUE,
            0, 1, 858993459, 858993459, 0, 715827882, 715827882, 0, 613566756, 613566756,
            0, Integer.MIN_VALUE, 0, 2, 477218588, 477218588, 0, 429496729, 429496729, 0,
            390451572, 390451572, 0, 357913941, 357913941, 0, 330382099, 330382099, 0, 306783378,
            306783378, 0, 286331153, 286331153, 0, Integer.MIN_VALUE, 0, 3, 252645135, 252645135,
            0, 238609294, 238609294, 0, 226050910, 226050910, 0, 214748364, 214748364, 0,
            204522252, 204522252, 0, 195225786, 195225786, 0, 186737708, 186737708, 0, 178956970,
            178956970, 0, 171798691, 171798691, 0, 165191049, 165191049, 0, 159072862, 159072862,
            0, 153391689, 153391689, 0, 148102320, 148102320, 0, 143165576, 143165576, 0,
            138547332, 138547332, 0, Integer.MIN_VALUE, 0, 4, 130150524, 130150524, 0, 126322567,
            126322567, 0, 122713351, 122713351, 0, 119304647, 119304647, 0, 116080197, 116080197,
            0, 113025455, 113025455, 0, 110127366, 110127366, 0, 107374182, 107374182, 0,
            104755299, 104755299, 0, 102261126, 102261126, 0, 99882960, 99882960, 0, 97612893,
            97612893, 0, 95443717, 95443717, 0, 93368854, 93368854, 0, 91382282, 91382282,
            0, 89478485, 89478485, 0, 87652393, 87652393, 0, 85899345, 85899345, 0,
            84215045, 84215045, 0, 82595524, 82595524, 0, 81037118, 81037118, 0, 79536431,
            79536431, 0, 78090314, 78090314, 0, 76695844, 76695844, 0, 75350303, 75350303,
            0, 74051160, 74051160, 0, 72796055, 72796055, 0, 71582788, 71582788, 0,
            70409299, 70409299, 0, 69273666, 69273666, 0, 68174084, 68174084, 0, Integer.MIN_VALUE,
            0, 5};

    public static long[] encodeBlocks(int[] blocks, int bitsPerEntry) {
        final long maxEntryValue = (1L << bitsPerEntry) - 1;
        final char valuesPerLong = (char) (64 / bitsPerEntry);
        final int magicIndex = 3 * (valuesPerLong - 1);
        final long divideMul = Integer.toUnsignedLong(MAGIC[magicIndex]);
        final long divideAdd = Integer.toUnsignedLong(MAGIC[magicIndex + 1]);
        final int divideShift = MAGIC[magicIndex + 2];
        final int size = (blocks.length + valuesPerLong - 1) / valuesPerLong;

        long[] data = new long[size];

        for (int i = 0; i < blocks.length; i++) {
            final long value = blocks[i];
            final int cellIndex = (int) (i * divideMul + divideAdd >> 32L >> divideShift);
            final int bitIndex = (i - cellIndex * valuesPerLong) * bitsPerEntry;
            data[cellIndex] = data[cellIndex] & ~(maxEntryValue << bitIndex) | (value & maxEntryValue) << bitIndex;
        }

        return data;
    }

}