Bsnes new - delegate refactoring

Fix reliance on GetFields() ordering which, per MDN, is unspecified.
CallingConventionAdapters.MakeWaterbox(...) doesn't care what order they're in, but snes_set_callbacks(...) does.

src/BizHawk.BizInvoke/BizInvoker.cs

@@ -81,7 +81,7 @@ namespace BizHawk.BizInvoke
 			var aname = new AssemblyName("BizInvokeProxyAssembly");
 			ImplAssemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(aname, AssemblyBuilderAccess.Run);
 			ImplModuleBuilder = ImplAssemblyBuilder.DefineDynamicModule("BizInvokerModule");
-			ClassFieldOffset = BizInvokerUtilities.ComputeClassFieldOffset();
+			ClassFieldOffset = BizInvokerUtilities.ComputeClassFirstFieldOffset();
 			StringOffset = BizInvokerUtilities.ComputeStringOffset();
 		}
 

src/BizHawk.BizInvoke/BizInvokerUtilities.cs

@@ -1,5 +1,8 @@
 using System;
+using System.Reflection;
+using System.Reflection.Emit;
 using System.Runtime.InteropServices;
+using System.Runtime.Serialization;
 
 namespace BizHawk.BizInvoke
 {
@@ -44,21 +47,18 @@ namespace BizHawk.BizInvoke
 		}
 
 		/// <summary>
-		/// Didn't I have code somewhere else to do this already?
+		/// Computes the byte offset of the first field of any class relative to a class pointer.
 		/// </summary>
 		/// <returns></returns>
-		public static int ComputeClassFieldOffset()
+		public static int ComputeClassFirstFieldOffset()
 		{
-			var c = new CF();
-			int ret;
-			fixed(int* fx = &c.FirstField)
-			{
-				U u = new(new U2(c));
-				ret = (int) ((ulong) (UIntPtr) fx - (ulong) u.First!.P);
-			}
-			return ret;
+			return ComputeFieldOffset(typeof(CF).GetField("FirstField"));
 		}
 
+		/// <summary>
+		/// Compute the byte offset of the first byte of string data (UTF16) relative to a pointer to the string.
+		/// </summary>
+		/// <returns></returns>
 		public static int ComputeStringOffset()
 		{
 			var s = new string(new char[0]);
@@ -70,5 +70,34 @@ namespace BizHawk.BizInvoke
 			}
 			return ret;
 		}
+
+		/// <summary>
+		/// Compute the byte offset of a field relative to a pointer to the class instance.
+		/// Slow, so cache it if you need it.
+		/// </summary>
+		public static int ComputeFieldOffset(FieldInfo fi)
+		{
+			if (fi.DeclaringType.IsValueType)
+			{
+				throw new NotImplementedException("Only supported for class fields right now");
+			}
+
+			var obj = FormatterServices.GetUninitializedObject(fi.DeclaringType);
+			var method = new DynamicMethod("ComputeFieldOffsetHelper", typeof(int), new[] { typeof(object) }, typeof(string).Module, true);
+			var il = method.GetILGenerator();
+			var local = il.DeclareLocal(fi.DeclaringType, true);
+			il.Emit(OpCodes.Ldarg_0);
+			il.Emit(OpCodes.Stloc, local);
+			il.Emit(OpCodes.Ldarg_0);
+			il.Emit(OpCodes.Ldflda, fi);
+			il.Emit(OpCodes.Conv_I);
+			il.Emit(OpCodes.Ldarg_0);
+			il.Emit(OpCodes.Conv_I);
+			il.Emit(OpCodes.Sub);
+			il.Emit(OpCodes.Conv_I4);
+			il.Emit(OpCodes.Ret);
+			var del = (Func<object, int>)method.CreateDelegate(typeof(Func<object, int>));
+			return del(obj);
+		}
 	}
 }

src/BizHawk.Emulation.Cores/Consoles/Nintendo/BSNES/BsnesApi.cs

@@ -7,6 +7,7 @@ using BizHawk.Common;
 using BizHawk.Emulation.Cores.Waterbox;
 using BizHawk.BizInvoke;
 using BizHawk.Emulation.Common;
+using System.Linq;
 
 namespace BizHawk.Emulation.Cores.Nintendo.BSNES
 {
@@ -92,12 +93,10 @@ namespace BizHawk.Emulation.Cores.Nintendo.BSNES
 
 		public void SetCallbacks(SnesCallbacks callbacks)
 		{
-			FieldInfo[] fieldInfos = typeof(SnesCallbacks).GetFields();
-			IntPtr[] functionPointerArray = new IntPtr[fieldInfos.Length];
-			for (int i = 0; i < fieldInfos.Length; i++)
-			{
-				functionPointerArray[i] = _adapter.GetFunctionPointerForDelegate((Delegate) fieldInfos[i].GetValue(callbacks));
-			}
+			var functionPointerArray = callbacks
+				.AllDelegatesInMemoryOrder()
+				.Select(f => _adapter.GetFunctionPointerForDelegate(f))
+				.ToArray();
 			core.snes_set_callbacks(functionPointerArray);
 		}
 
@@ -167,6 +166,21 @@ namespace BizHawk.Emulation.Cores.Nintendo.BSNES
 			public snes_audio_sample_t audioSampleCb;
 			public snes_path_request_t pathRequestCb;
 			public snes_trace_t snesTraceCb;
+
+			private static List<FieldInfo> FieldsInOrder = null;
+
+			public IEnumerable<Delegate> AllDelegatesInMemoryOrder()
+			{
+				if (FieldsInOrder == null)
+				{
+					FieldsInOrder = GetType()
+						.GetFields()
+						.OrderBy(fi => BizInvokerUtilities.ComputeFieldOffset(fi))
+						.ToList();
+				}
+				return FieldsInOrder
+					.Select(f => (Delegate)f.GetValue(this));
+			}
 		}
 
 		public void Seal()
@@ -186,7 +200,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.BSNES
 		public void SaveStateBinary(BinaryWriter writer)
 		{
 			// if (serializedSize == 0)
-				// serializedSize = _core.snes_serialized_size();
+			// serializedSize = _core.snes_serialized_size();
 			// TODO: do some profiling and testing to check whether this is actually better than _exe.SaveStateBinary(writer);
 			// re-adding bsnes's own serialization will need to be done once it's confirmed to be deterministic, aka after libco update
 

src/BizHawk.Emulation.Cores/Consoles/Nintendo/BSNES/BsnesCore.cs

@@ -59,16 +59,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.BSNES
 				snesTraceCb = snes_trace
 			};
 
-			Api = new BsnesApi(CoreComm.CoreFileProvider.DllPath(), CoreComm, new Delegate[]
-			{
-				callbacks.inputPollCb,
-				callbacks.inputStateCb,
-				callbacks.noLagCb,
-				callbacks.videoFrameCb,
-				callbacks.audioSampleCb,
-				callbacks.pathRequestCb,
-				callbacks.snesTraceCb
-			});
+			Api = new BsnesApi(CoreComm.CoreFileProvider.DllPath(), CoreComm, callbacks.AllDelegatesInMemoryOrder());
 
 			_controllers = new BsnesControllers(_syncSettings);