From 98afdb899366e44b391190aff7ec3e7556d3c519 Mon Sep 17 00:00:00 2001
From: CasualPokePlayer <50538166+CasualPokePlayer@users.noreply.github.com>
Date: Sat, 15 Apr 2023 22:04:21 -0700
Subject: [PATCH] (Actually) Fix DeltaSerializer's `GetDelta`

fixes 2838a5412ae470bf90c47e15331a4607d89a36ea
---
 src/BizHawk.Common/DeltaSerializer.cs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/BizHawk.Common/DeltaSerializer.cs b/src/BizHawk.Common/DeltaSerializer.cs
index 5003046791..c69d0fed54 100644
--- a/src/BizHawk.Common/DeltaSerializer.cs
+++ b/src/BizHawk.Common/DeltaSerializer.cs
@@ -69,6 +69,8 @@ namespace BizHawk.Common
 
 					if (different > 0) // only not 0 if index == end immediately
 					{
+						different = index - blockStart - same;
+	
 						if (same < 4) // we have different bytes, but we hit the end of the spans before the 8 limit, and we have less than what a same block will save
 						{
 							different += same;
@@ -82,6 +84,8 @@ namespace BizHawk.Common
 						{
 							ret[retSize++] = (byte)(orignalAsBytes[i] ^ currentAsBytes[i]);
 						}
+
+						blockStart = index - same;
 					}
 
 					if (same > 0) // same is 4-8, 8 indicates we hit the 8 same bytes threshold, 4-7 indicate hit end of span
@@ -91,10 +95,10 @@ namespace BizHawk.Common
 							while (index < end && orignalAsBytes[index] == currentAsBytes[index])
 							{
 								index++;
-								same++;
 							}
 						}
 
+						same = index - blockStart;
 						MemoryMarshal.Write(ret.Slice(retSize, 4), ref same);
 						retSize += 4;
 					}