Add unit tests for CRC32 impls

src/BizHawk.Tests/Common/checksums/CRC32Tests.cs

@@ -0,0 +1,49 @@
+using BizHawk.Common;
+using BizHawk.Emulation.DiscSystem;
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace BizHawk.Tests.Common.checksums
+{
+	[TestClass]
+	public sealed class CRC32Tests
+	{
+		private const uint EXPECTED = 0xDA3BA10AU;
+
+		private const uint EXPECTED_COMBINED = 0xED182BB0U;
+
+		private const uint EXPECTED_EXTRA = 0x29058C73U;
+
+		[TestMethod]
+		public void TestCRC32Stability()
+		{
+			static byte[] InitialiseArray()
+			{
+				var a = new byte[0x100];
+				for (var i = 0; i < 0x100; i++) a[i] = (byte) ~i;
+				return a;
+			}
+			static byte[] InitialiseArrayExtra()
+			{
+				var a = new byte[0x100];
+				for (var i = 0; i < 0x100; i++) a[i] = (byte) i;
+				return a;
+			}
+
+			var data = InitialiseArray();
+			Assert.AreEqual(EXPECTED, (uint) CRC32.Calculate(data));
+
+			data = InitialiseArray();
+			DiscHasher.SpecialCRC32 crc32 = new();
+			crc32.Add(data, 0, data.Length);
+			Assert.AreEqual(EXPECTED, crc32.Result);
+
+			var dataExtra = InitialiseArrayExtra();
+			DiscHasher.SpecialCRC32 crc32Extra = new();
+			crc32Extra.Add(dataExtra, 0, dataExtra.Length);
+			Assert.AreEqual(EXPECTED_EXTRA, crc32Extra.Result);
+			crc32.Incorporate(crc32Extra.Result, dataExtra.Length);
+			Assert.AreEqual(EXPECTED_COMBINED, crc32.Result);
+		}
+	}
+}