From be0a456067cdfbeabe5855bddf949d67603472a2 Mon Sep 17 00:00:00 2001
From: Kurt <kaphotics@gmail.com>
Date: Fri, 17 Apr 2020 14:00:34 -0700
Subject: [PATCH] Decrypt savefile in-place (less allocation)

Each player and main.dat is ~11MB of allocation to read; old would read & decrypt into separate array = 22MB * (1 + playerCount). Cutting this in half reduces the amount of allocation and keeps stuff off gen2 LOH
---
 NHSE.Core/Encryption/Encryption.cs       | 9 +++------
 NHSE.Core/Save/Meta/EncryptedFilePair.cs | 8 ++++----
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/NHSE.Core/Encryption/Encryption.cs b/NHSE.Core/Encryption/Encryption.cs
index 9efd23d..4537c09 100644
--- a/NHSE.Core/Encryption/Encryption.cs
+++ b/NHSE.Core/Encryption/Encryption.cs
@@ -21,12 +21,11 @@ private static byte[] GetParam(uint[] data, in int index)
         }
 
         /// <summary>
-        /// Decrypts the <see cref="encData"/> using the <see cref="headerData"/>.
+        /// Decrypts the <see cref="encData"/> using the <see cref="headerData"/> in place.
         /// </summary>
         /// <param name="headerData">Header Data</param>
         /// <param name="encData">Encrypted SaveData</param>
-        /// <returns>Decrypted SaveData</returns>
-        public static byte[] Decrypt(byte[] headerData, byte[] encData)
+        public static void Decrypt(byte[] headerData, byte[] encData)
         {
             // First 256 bytes go unused
             var importantData = new uint[0x80];
@@ -41,10 +40,8 @@ public static byte[] Decrypt(byte[] headerData, byte[] encData)
             // Do the AES
             using var aesCtr = new Aes128CounterMode(counter);
             var transform = aesCtr.CreateDecryptor(key, counter);
-            var decData = new byte[encData.Length];
 
-            transform.TransformBlock(encData, 0, encData.Length, decData, 0);
-            return decData;
+            transform.TransformBlock(encData, 0, encData.Length, encData, 0);
         }
 
         private static CryptoFile GenerateHeaderFile(uint seed, byte[] versionData)
diff --git a/NHSE.Core/Save/Meta/EncryptedFilePair.cs b/NHSE.Core/Save/Meta/EncryptedFilePair.cs
index d4338a5..b851131 100644
--- a/NHSE.Core/Save/Meta/EncryptedFilePair.cs
+++ b/NHSE.Core/Save/Meta/EncryptedFilePair.cs
@@ -29,10 +29,10 @@ protected EncryptedFilePair(string folder, string name)
             var hd = File.ReadAllBytes(hdr);
             var md = File.ReadAllBytes(dat);
 
-            var decrypted = Encryption.Decrypt(hd, md);
+            Encryption.Decrypt(hd, md);
 
             Header = hd;
-            Data = decrypted;
+            Data = md;
             DataPath = dat;
             HeaderPath = hdr;
 
@@ -76,7 +76,7 @@ public IEnumerable<FileHashRegion> InvalidHashes()
             }
         }
 
-        public string GetString(int offset, int maxLength) => StringUtil.GetString(Data, offset, maxLength);
-        public static byte[] GetBytes(string value, int maxLength) => StringUtil.GetBytes(value, maxLength);
+        protected string GetString(int offset, int maxLength) => StringUtil.GetString(Data, offset, maxLength);
+        protected static byte[] GetBytes(string value, int maxLength) => StringUtil.GetBytes(value, maxLength);
     }
 }
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