From 85e91d722ce6700e23d9c6315f0de82a030a1752 Mon Sep 17 00:00:00 2001
From: SuuperW <SuuperW@gmail.com>
Date: Mon, 23 Dec 2019 10:05:36 -0600
Subject: [PATCH] NDS's firmware file contains user settings; these are
 over-written by sync settings, so we shouldn't allow them to impact the hash

---
 BizHawk.Client.Common/FirmwareManager.cs      |  9 ++++++--
 .../Database/FirmwareDatabase.cs              |  3 +--
 .../Consoles/Nintendo/NDS/MelonDS.cs          | 23 ++++++++++++++++++-
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/BizHawk.Client.Common/FirmwareManager.cs b/BizHawk.Client.Common/FirmwareManager.cs
index d6dc3040fa..136c5714c2 100644
--- a/BizHawk.Client.Common/FirmwareManager.cs
+++ b/BizHawk.Client.Common/FirmwareManager.cs
@@ -259,8 +259,13 @@ namespace BizHawk.Client.Common
 							continue;
 						}
 
-						// compute its hash 
-						var rff = reader.Read(fi);
+						// compute its hash
+						RealFirmwareFile rff;
+						// NDS's firmware file contains user settings; these are over-written by sync settings, so we shouldn't allow them to impact the hash
+						if (fr.SystemId == "NDS" && fr.FirmwareId == "firmware")
+							rff = reader.Read(new FileInfo(Emulation.Cores.Consoles.Nintendo.NDS.MelonDS.CreateModifiedFirmware(userSpec)));
+						else
+							rff = reader.Read(fi);
 						ri.Size = fi.Length;
 						ri.Hash = rff.Hash;
 
diff --git a/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs b/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs
index f2f143cb10..d0879103d1 100644
--- a/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs
+++ b/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs
@@ -44,8 +44,7 @@ namespace BizHawk.Emulation.Common
 
 			FirmwareAndOption("24F67BDEA115A2C847C8813A262502EE1607B7DF", 16384, "NDS", "bios7", "bios7.bin", "ARM7 BIOS");
 			FirmwareAndOption("BFAAC75F101C135E32E2AAF541DE6B1BE4C8C62D", 4096, "NDS", "bios9", "bios9.bin", "ARM9 BIOS");
-			// NDS firmware dump contains user settings, so hashes are not expected to match
-			FirmwareAndOption("0000000000000000000000000000000000000000", 262144, "NDS", "firmware", "firmware.bin", "NDS Firmware");
+			FirmwareAndOption("DDDDA2447AE84A77385497D8889516E8BC090418", 262144, "NDS", "firmware", "firmware.bin", "NDS Firmware (note: given hash is with blank user data)");
 
 			FirmwareAndOption("E4ED47FAE31693E016B081C6BDA48DA5B70D7CCB", 512, "Lynx", "Boot", "lynxboot.img", "Boot Rom");
 
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs
index e425773a91..36874b2c64 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs
@@ -11,7 +11,7 @@ using BizHawk.Emulation.Common;
 namespace BizHawk.Emulation.Cores.Consoles.Nintendo.NDS
 {
 	[Core("MelonDS", "Arisotura")]
-	unsafe partial class MelonDS : IEmulator
+	unsafe public partial class MelonDS : IEmulator
 	{
 		private BasicServiceProvider _serviceProvider;
 		public IEmulatorServiceProvider ServiceProvider => _serviceProvider;
@@ -139,5 +139,26 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.NDS
 			else
 				File.Delete("melon/firmware.bin");
 		}
+
+		/// <summary>
+		/// Creates a modified copy of the given firmware file, with the user settings erased.
+		/// </summary>
+		/// <returns>Returns a path to the new file.</returns>
+		public static string CreateModifiedFirmware(string firmwarePath)
+		{
+			const string newPath = "melon/tohash.bin";
+			byte[] bytes = File.ReadAllBytes(firmwarePath);
+
+			// There are two regions for user settings
+			int settingsLength = getUserSettingsLength();
+			for (int i = bytes.Length - 0x200; i < bytes.Length - 0x200 + settingsLength; i++)
+				bytes[i] = 0xFF;
+			for (int i = bytes.Length - 0x100; i < bytes.Length - 0x100 + settingsLength; i++)
+				bytes[i] = 0xFF;
+
+
+			File.WriteAllBytes(newPath, bytes);
+			return newPath;
+		}
 	}
 }