Use OpenRA CRC32

OpenRA.Game/FileFormats/CRC32.cs

@@ -11,7 +11,7 @@
 
 using System;
 
-namespace OpenRA.Mods.Cnc.FileFormats
+namespace OpenRA.FileFormats
 {
 	/// <summary>
 	/// Static class that uses a lookup table to calculates CRC32
@@ -118,5 +118,16 @@ namespace OpenRA.Mods.Cnc.FileFormats
 		{
 			return Calculate(data, 0xFFFFFFFF);
 		}
+
+		// Chaining method: accepts the current CRC state
+		public static uint Update(uint crc, ReadOnlySpan<byte> data)
+		{
+			for (var i = 0; i < data.Length; i++)
+				crc = (crc >> 8) ^ LookUp[(crc & 0xFF) ^ data[i]];
+			return crc;
+		}
+
+		// Standard PNG start: 0xFFFFFFFF, Finalize: XOR 0xFFFFFFFF
+		public static uint Finish(uint crc) => crc ^ 0xFFFFFFFF;
 	}
 }

OpenRA.Game/FileFormats/Png.cs

@@ -15,7 +15,6 @@ using System.IO;
 using System.Linq;
 using System.Net;
 using System.Text;
-using ICSharpCode.SharpZipLib.Checksum;
 using ICSharpCode.SharpZipLib.Zip.Compression;
 using ICSharpCode.SharpZipLib.Zip.Compression.Streams;
 using OpenRA.Graphics;
@@ -333,10 +332,12 @@ namespace OpenRA.FileFormats
 			var data = input.ReadAllBytes();
 			output.Write(data);
 
-			var crc32 = new Crc32();
-			crc32.Update(typeBytes);
-			crc32.Update(data);
-			output.Write(IPAddress.NetworkToHostOrder((int)crc32.Value));
+			var crc = 0xFFFFFFFF;
+			crc = CRC32.Update(crc, typeBytes);
+			crc = CRC32.Update(crc, data);
+			var finalCrc = CRC32.Finish(crc);
+
+			output.Write(IPAddress.NetworkToHostOrder((int)finalCrc));
 		}
 
 		public byte[] Save(Compression compression = Compression.BEST_COMPRESSION)

OpenRA.Mods.Cnc/FileSystem/PackageEntry.cs

@@ -14,7 +14,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Text;
-using OpenRA.Mods.Cnc.FileFormats;
+using OpenRA.FileFormats;
 
 namespace OpenRA.Mods.Cnc.FileSystem
 {