Move ZwinderBuffer invalidation logic into the class (#4066)

in scenarios with MANY states and high fps, the overhead of calling `GetState` every time was significant.

src/BizHawk.Client.Common/movie/tasproj/ZwinderStateManager.cs

@@ -437,7 +437,7 @@ namespace BizHawk.Client.Common
 				else
 					StateCache.Remove(lastGap.Frame);
 
-				_gapFiller.InvalidateEnd(i);
+				_gapFiller.InvalidateLast();
 			}
 
 			_gapFiller.Capture(
@@ -461,9 +461,9 @@ namespace BizHawk.Client.Common
 
 		public void Clear()
 		{
-			_current.InvalidateEnd(0);
-			_recent.InvalidateEnd(0);
-			_gapFiller.InvalidateEnd(0);
+			_current.InvalidateAfter(-1);
+			_recent.InvalidateAfter(-1);
+			_gapFiller.InvalidateAfter(-1);
 			StateCache.Clear();
 			AddStateCache(0);
 			_reserved = _reserved.Where(static kvp => kvp.Key is 0).ToDictionary(); //TODO clone needed?
@@ -485,39 +485,18 @@ namespace BizHawk.Client.Common
 
 		private bool InvalidateGaps(int frame)
 		{
-			for (var i = 0; i < _gapFiller.Count; i++)
-			{
-				var state = _gapFiller.GetState(i);
-				if (state.Frame > frame)
-				{
-					_gapFiller.InvalidateEnd(i);
-					return true;
-				}
-			}
-			return false;
+			return _gapFiller.InvalidateAfter(frame);
 		}
 
 		private bool InvalidateNormal(int frame)
 		{
-			for (var i = 0; i < _recent.Count; i++)
+			if (_recent.InvalidateAfter(frame))
 			{
-				if (_recent.GetState(i).Frame > frame)
-				{
-					_recent.InvalidateEnd(i);
-					_current.InvalidateEnd(0);
-					return true;
-				}
+				_current.InvalidateAfter(-1);
+				return true;
 			}
 
-			for (var i = 0; i < _current.Count; i++)
-			{
-				if (_current.GetState(i).Frame > frame)
-				{
-					_current.InvalidateEnd(i);
-					return true;
-				}
-			}
-			return false;
+			return _current.InvalidateAfter(frame);
 		}
 
 		private bool InvalidateReserved(int frame)

src/BizHawk.Client.Common/rewind/ZeldaWinder.cs

@@ -84,7 +84,7 @@ namespace BizHawk.Client.Common
 		public void Clear()
 		{
 			Sync();
-			_buffer.InvalidateEnd(0);
+			_buffer.InvalidateAfter(-1);
 			_count = 0;
 			_masterFrame = -1;
 		}
@@ -236,7 +236,7 @@ namespace BizHawk.Client.Common
 				{
 					var index = _buffer.Count - 1;
 					RefillMaster(_buffer.GetState(index));
-					_buffer.InvalidateEnd(index);
+					_buffer.InvalidateLast();
 					_stateSource.LoadStateBinary(new BinaryReader(new MemoryStream(_master, 0, _masterLength, false)));
 				}
 				else

src/BizHawk.Client.Common/rewind/Zwinder.cs

@@ -74,7 +74,7 @@ namespace BizHawk.Client.Common
 				}
 				using var br = new BinaryReader(state.GetReadStream());
 				_stateSource.LoadStateBinary(br);
-				_buffer.InvalidateEnd(index);
+				_buffer.InvalidateLast();
 			}
 			else
 			{
@@ -103,7 +103,7 @@ namespace BizHawk.Client.Common
 
 		public void Clear()
 		{
-			_buffer.InvalidateEnd(0);
+			_buffer.InvalidateAfter(-1);
 		}
 	}
 }

src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs

@@ -284,18 +284,33 @@ namespace BizHawk.Client.Common
 		}
 
 		/// <summary>
-		/// Invalidate states from GetState(index) on to the end of the buffer, so that Count == index afterwards
+		/// Invalidate all states with frame number > frame.
+		/// <returns>True iff any state was invalidated, else false</returns>
 		/// </summary>
-		public void InvalidateEnd(int index)
+		public bool InvalidateAfter(int frame)
 		{
-			if ((uint) index > (uint) Count) // intentionally allows index == Count (e.g. clearing an empty buffer)
+			for (int i = _firstStateIndex; i != _nextStateIndex; i = (i + 1) & STATEMASK)
 			{
-				throw new ArgumentOutOfRangeException(paramName: nameof(index), index, message: "index out of range");
+				if (_states[i].Frame > frame)
+				{
+					_nextStateIndex = (i + _firstStateIndex) & STATEMASK;
+					return true;
+				}
 			}
-			_nextStateIndex = (index + _firstStateIndex) & STATEMASK;
+
+			return false;
 			//Util.DebugWriteLine($"Size: {Size >> 20}MiB, Used: {Used >> 20}MiB, States: {Count}");
 		}
 
+		/// <summary>
+		/// Invalidates the last state in the buffer
+		/// </summary>
+		public void InvalidateLast()
+		{
+			if (Count != 0)
+				_nextStateIndex = (_nextStateIndex - 1) & STATEMASK;
+		}
+
 		public void SaveStateBinary(BinaryWriter writer)
 		{
 			// version number