From 3db2fe8d63162c716b8ac57ae0898027ecd3a7bb Mon Sep 17 00:00:00 2001
From: Andrew Steinborn <git@steinborn.me>
Date: Mon, 3 May 2021 17:31:32 -0400
Subject: [PATCH] Optimize varint writing

Inspired by the approach described at the bottom of https://richardstartin.github.io/posts/dont-use-protobuf-for-telemetry

Given that we do a lot of varint writing as well, this should provide a small performance boost for larger/complex packets whilst not regressing hard on smaller packets.
---
 .../proxy/protocol/ProtocolUtils.java         | 26 ++++++++++++++-----
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/proxy/src/main/java/com/velocitypowered/proxy/protocol/ProtocolUtils.java b/proxy/src/main/java/com/velocitypowered/proxy/protocol/ProtocolUtils.java
index 50f6c48d0..f7424b05b 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/protocol/ProtocolUtils.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/protocol/ProtocolUtils.java
@@ -62,6 +62,17 @@ public enum ProtocolUtils {
   private static final int DEFAULT_MAX_STRING_SIZE = 65536; // 64KiB
   private static final QuietDecoderException BAD_VARINT_CACHED =
       new QuietDecoderException("Bad varint decoded");
+  private static final int[] VAR_INT_LENGTHS = new int[33];
+
+  static {
+    // Inspired by https://richardstartin.github.io/posts/dont-use-protobuf-for-telemetry
+    //
+    // This has been slightly modified in that we reduce the length to 32-bit only, since Velocity
+    // doesn't look at any part of the Minecraft protocol that requires us to look at VarLongs.
+    for (int i = 0; i <= 32; ++i) {
+      VAR_INT_LENGTHS[i] = (31 - i) / 7;
+    }
+  }
 
   /**
    * Reads a Minecraft-style VarInt from the specified {@code buf}.
@@ -97,21 +108,22 @@ public enum ProtocolUtils {
     return Integer.MIN_VALUE;
   }
 
+  public static int varintBytes(int value) {
+    return VAR_INT_LENGTHS[Integer.numberOfLeadingZeros(value)];
+  }
+
   /**
    * Writes a Minecraft-style VarInt to the specified {@code buf}.
    * @param buf the buffer to read from
    * @param value the integer to write
    */
   public static void writeVarInt(ByteBuf buf, int value) {
-    while (true) {
-      if ((value & 0xFFFFFF80) == 0) {
-        buf.writeByte(value);
-        return;
-      }
-
-      buf.writeByte(value & 0x7F | 0x80);
+    int length = varintBytes(value);
+    for (int i = 0; i < length; ++i) {
+      buf.writeByte(((byte) ((value & 0x7F) | 0x80)));
       value >>>= 7;
     }
+    buf.writeByte((byte) value);
   }
 
   public static String readString(ByteBuf buf) {