From 8b02f05bd5ce1bb153dbd1dd75782613e5f36631 Mon Sep 17 00:00:00 2001
From: Kurt <kaphotics@gmail.com>
Date: Tue, 26 Sep 2017 23:10:31 -0700
Subject: [PATCH] Faster crc16 ccitt

insert lenny face here
>4x faster, relative speed is higher for larger input arrays
---
 PKHeX.Core/Saves/SaveUtil.cs | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/PKHeX.Core/Saves/SaveUtil.cs b/PKHeX.Core/Saves/SaveUtil.cs
index a0cca1a8e..7c02f0397 100644
--- a/PKHeX.Core/Saves/SaveUtil.cs
+++ b/PKHeX.Core/Saves/SaveUtil.cs
@@ -608,24 +608,17 @@ public static bool GetSavesFromFolder(string folderPath, bool deep, out IEnumera
         /// <returns>Checksum</returns>
         public static ushort CRC16_CCITT(byte[] data, int start, int length)
         {
-            const ushort init = 0xFFFF;
-            const ushort poly = 0x1021;
-
-            ushort crc = init;
+            byte top = 0xFF;
+            byte bot = 0xFF;
             int end = start + length;
             for (int i = start; i < end; i++)
             {
-                byte b = data[i];
-                crc ^= (ushort)(b << 8);
-                for (int j = 0; j < 8; j++)
-                {
-                    bool flag = (crc & 0x8000) > 0;
-                    crc <<= 1;
-                    if (flag)
-                        crc ^= poly;
-                }
+                var x = data[i] ^ top;
+                x ^= (x >> 4);
+                top = (byte) (bot ^ (x >> 3) ^ (x << 4));
+                bot = (byte) (x ^ (x << 5));
             }
-            return crc;
+            return (ushort)(top << 8 | bot);
         }
 
         /// <summary>Calculates the CRC16-CCITT checksum over an input byte array.</summary>