PaperMC/paper-server/patches/sources/net/minecraft/network/VarInt.java.patch

--- a/net/minecraft/network/VarInt.java
+++ b/net/minecraft/network/VarInt.java
@@ -9,6 +_,18 @@
     private static final int DATA_BITS_PER_BYTE = 7;
 
     public static int getByteSize(int data) {
+    // Paper start - Optimize VarInts
+        return VARINT_EXACT_BYTE_LENGTHS[Integer.numberOfLeadingZeros(data)];
+    }
+    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.
+    }
+    public static int getByteSizeOld(int data) {
+    // Paper end - Optimize VarInts
         for (int i = 1; i < 5; i++) {
             if ((data & -1 << i * 7) == 0) {
                 return i;
@@ -39,6 +_,21 @@
     }
 
     public static ByteBuf write(ByteBuf buffer, int value) {
+     // Paper start - Optimize VarInts
+        // 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) {
+            buffer.writeByte(value);
+        } else if ((value & (0xFFFFFFFF << 14)) == 0) {
+            int w = (value & 0x7F | 0x80) << 8 | (value >>> 7);
+            buffer.writeShort(w);
+        } else {
+            writeOld(buffer, value);
+        }
+        return buffer;
+    }
+    public static ByteBuf writeOld(ByteBuf buffer, int value) {
+    // Paper end - Optimize VarInts
         while ((value & -128) != 0) {
             buffer.writeByte(value & 127 | 128);
             value >>>= 7;