Velocity's varint reading/writing optimizations

api/src/main/java/com/github/retrooper/packetevents/netty/buffer/ByteBufHelper.java

@@ -23,6 +23,7 @@
 import java.nio.charset.Charset;
 
 public class ByteBufHelper {
+
     public static int capacity(Object buffer) {
         return PacketEvents.getAPI().getNettyManager().getByteBufOperator().capacity(buffer);
     }
@@ -239,29 +240,82 @@ public static Object resetWriterIndex(Object buffer) {
         return PacketEvents.getAPI().getNettyManager().getByteBufOperator().resetWriterIndex(buffer);
     }
 
-    public static int readVarInt(Object buffer) {
-        int value = 0;
-        int length = 0;
-        byte currentByte;
-        do {
-            currentByte = readByte(buffer);
-            value |= (currentByte & 0x7F) << (length * 7);
-            length++;
-            if (length > 5) {
-                throw new RuntimeException("VarInt is too large. Must be smaller than 5 bytes.");
-            }
-        } while ((currentByte & 0x80) == 0x80);
-        return value;
-    }
-
-    public static void writeVarInt(Object buffer, int value) {
-        while (true) {
-            if ((value & ~0x7F) == 0) {
-                writeByte(buffer, value);
-                return;
-            }
-            writeByte(buffer, (value & 0x7F) | 0x80);
-            value >>>= 7;
+    public static int getIntLE(Object buffer, int readerIndex) {
+        return PacketEvents.getAPI().getNettyManager().getByteBufOperator().getIntLE(buffer, readerIndex);
+    }
+
+    //Src: https://github.com/jonesdevelopment/sonar/blob/main/common/src/main/java/xyz/jonesdev/sonar/common/fallback/netty/FallbackVarInt21FrameDecoder.java#L69
+    public static int readVarInt(Object buf) {
+        if (readableBytes(buf) < 4) return readVarIntSmallBuffer(buf);
+
+        // take the last three bytes and check if any of them have the high bit set
+        int wholeOrMore = getIntLE(buf, readerIndex(buf));
+        int atStop = ~wholeOrMore & 0x808080;
+        if (atStop == 0) throw new RuntimeException("fucked up - VarInt too big");
+
+        final int bitsToKeep = Integer.numberOfTrailingZeros(atStop) + 1;
+        skipBytes(buf, bitsToKeep >> 3);
+
+        // https://github.com/netty/netty/pull/14050#issuecomment-2107750734
+        int preservedBytes = wholeOrMore & (atStop ^ (atStop - 1));
+
+        // https://github.com/netty/netty/pull/14050#discussion_r1597896639
+        preservedBytes = (preservedBytes & 0x007F007F) | ((preservedBytes & 0x00007F00) >> 1);
+        preservedBytes = (preservedBytes & 0x00003FFF) | ((preservedBytes & 0x3FFF0000) >> 2);
+        return preservedBytes;
+    }
+
+    //fallback to unrolled loop
+    //I'll try to optimize this in the future
+    private static int readVarIntSmallBuffer(Object buf) {
+        if (!isReadable(buf)) return 0;
+
+        int rIdx = readerIndex(buf);
+
+        byte tmp = readByte(buf);
+        if (tmp >= 0) return tmp;
+
+        int result = tmp & 0x7F;
+        if (!isReadable(buf)) {
+            readerIndex(buf, rIdx);
+            return 0;
+        }
+
+        if ((tmp = readByte(buf)) >= 0) return result | tmp << 7;
+
+        result |= (tmp & 0x7F) << 7;
+        if (!isReadable(buf)) {
+            readerIndex(buf, rIdx);
+            return 0;
+        }
+        if ((tmp = readByte(buf)) >= 0) return result | tmp << 14;
+
+        return result | (tmp & 0x7F) << 14;
+    }
+
+    //Src: https://steinborn.me/posts/performance/how-fast-can-you-write-a-varint/
+    public static void writeVarInt(Object buf, int i) {
+        if ((i & (0xFFFFFFFF << 7)) == 0) {
+            // 1 byte case
+            writeByte(buf, i);
+        } else if ((i & (0xFFFFFFFF << 14)) == 0) {
+            // 2 byte case
+            int w = (i & 0x7F | 0x80) << 8 | (i >>> 7);
+            writeShort(buf, w);
+        } else if ((i & (0xFFFFFFFF << 21)) == 0) {
+            // 3 byte case
+            int w = ((i & 0x7F | 0x80) << 16) | ((i >>> 7 & 0x7F | 0x80) << 8) | (i >>> 14);
+            writeMedium(buf, w);
+        } else if ((i & (0xFFFFFFFF << 28)) == 0) {
+            // 4 byte case
+            int w = ((i & 0x7F | 0x80) << 24) | ((i >>> 7 & 0x7F | 0x80) << 16) | ((i >>> 14 & 0x7F | 0x80) << 8) | (i >>> 21);
+            writeInt(buf, w);
+        } else {
+            // 5 byte case (the max size for a VarInt)
+            // Write the first 4 bytes as an int
+            int w = ((i & 0x7F | 0x80) << 24) | ((i >>> 7 & 0x7F | 0x80) << 16) | ((i >>> 14 & 0x7F | 0x80) << 8) | (i >>> 21 & 0x7F | 0x80);
+            writeInt(buf, w); // Write the first 4 bytes
+            writeByte(buf, i >>> 28); // Write the remaining 5th byte
         }
     }
 

api/src/main/java/com/github/retrooper/packetevents/netty/buffer/ByteBufOperator.java

@@ -49,6 +49,8 @@ public interface ByteBufOperator {
     Object getBytes(Object buffer, int index, byte[] destination);
     short getUnsignedByte(Object buffer, int index);
 
+    int getIntLE(Object buffer, int readerIndex);
+
     boolean isReadable(Object buffer);
     Object copy(Object buffer);
     Object duplicate(Object buffer);

api/src/main/java/com/github/retrooper/packetevents/wrapper/PacketWrapper.java

@@ -387,18 +387,7 @@ public void writeMedium(int value) {
     }
 
     public int readVarInt() {
-        int value = 0;
-        int length = 0;
-        byte currentByte;
-        do {
-            currentByte = readByte();
-            value |= (currentByte & 0x7F) << (length * 7);
-            length++;
-            if (length > 5) {
-                throw new RuntimeException("VarInt is too large. Must be smaller than 5 bytes.");
-            }
-        } while ((currentByte & 0x80) == 0x80);
-        return value;
+        return ByteBufHelper.readVarInt(this.buffer);//delegate to ByteBufHelper
     }
 
     public void writeVarInt(int value) {

netty-common/src/main/java/io/github/retrooper/packetevents/impl/netty/buffer/ByteBufOperatorImpl.java

@@ -99,6 +99,11 @@ public long readLong(Object buffer) {
         return ((ByteBuf)buffer).readLong();
     }
 
+    @Override
+    public int getIntLE(Object buffer, int readerIndex) {
+        return ((ByteBuf) buffer).getIntLE(readerIndex);
+    }
+
     @Override
     public void writeByte(Object buffer, int value) {
         ((ByteBuf)buffer).writeByte(value);

spigot/src/main/java/io/github/retrooper/packetevents/netty/buffer/ByteBufOperatorModernImpl.java

@@ -99,6 +99,11 @@ public long readLong(Object buffer) {
         return ((ByteBuf)buffer).readLong();
     }
 
+    @Override
+    public int getIntLE(Object buffer, int readerIndex) {
+        return ((ByteBuf) buffer).getIntLE(readerIndex);
+    }
+
 
     @Override
     public void writeByte(Object buffer, int value) {