From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Arthur Blanchot <blanchot.arthur@protonmail.ch>
Date: Sat, 16 Jul 2022 18:12:38 +0200
Subject: [PATCH] Implement Velocity VarInt optimizations

Original license: GPLv3
Original project: https://github.com/PaperMC/Velocity
Paper pull request: https://github.com/PaperMC/Paper/pull/6957

diff --git a/src/main/java/net/minecraft/network/FriendlyByteBuf.java b/src/main/java/net/minecraft/network/FriendlyByteBuf.java
index 35377576ed182814051c11f902e02e8e921e84e3..8747a55d8818d4526939070fa29a12ab643f0798 100644
--- a/src/main/java/net/minecraft/network/FriendlyByteBuf.java
+++ b/src/main/java/net/minecraft/network/FriendlyByteBuf.java
@@ -82,19 +82,22 @@ public class FriendlyByteBuf extends ByteBuf {
     private static final int PUBLIC_KEY_SIZE = 256;
     private static final int MAX_PUBLIC_KEY_HEADER_SIZE = 256;
     private static final int MAX_PUBLIC_KEY_LENGTH = 512;
+    // Mirai start - Optimize VarInts
+    private static final int[] VARINT_EXACT_BYTE_LENGTHS = new int[33];
+    static {
+        for (int i = 0; i <= 32; ++i) {
+            VARINT_EXACT_BYTE_LENGTHS[i] = (int) Math.ceil((31d - (i - 1)) / 7d);
+        }
+        VARINT_EXACT_BYTE_LENGTHS[32] = 1; // Special case for the number 0.
+    }
+    // Mirai end
 
     public FriendlyByteBuf(ByteBuf parent) {
         this.source = parent;
     }
 
     public static int getVarIntSize(int value) {
-        for (int j = 1; j < 5; ++j) {
-            if ((value & -1 << j * 7) == 0) {
-                return j;
-            }
-        }
-
-        return 5;
+        return VARINT_EXACT_BYTE_LENGTHS[Integer.numberOfLeadingZeros(value)]; // Mirai - Optimize VarInts
     }
 
     public static int getVarLongSize(long value) {
@@ -503,7 +506,23 @@ public class FriendlyByteBuf extends ByteBuf {
         return new UUID(this.readLong(), this.readLong());
     }
 
+    // Mirai start - Optimize VarInts
     public FriendlyByteBuf writeVarInt(int value) {
+        // Peel the one and two byte count cases explicitly as they are the most common VarInt sizes
+        // that the proxy will write, to improve inlining.
+        if ((value & (0xFFFFFFFF << 7)) == 0) {
+            writeByte(value);
+        } else if ((value & (0xFFFFFFFF << 14)) == 0) {
+            int w = (value & 0x7F | 0x80) << 8 | (value >>> 7);
+            writeShort(w);
+        } else {
+            writeVarInt_(value);
+        }
+        return this;
+    }
+
+    public FriendlyByteBuf writeVarInt_(int value) {
+    // Mirai end
         while ((value & -128) != 0) {
             this.writeByte(value & 127 | 128);
             value >>>= 7;