Move CRC32 impls to `BizHawk.Common/checksums`

src/BizHawk.Common/checksums/SpecialCRC32.cs

@@ -0,0 +1,138 @@
+#nullable disable
+
+using System;
+
+namespace BizHawk.Common
+{
+	/// <summary>
+	/// A stateful special CRC32 calculator
+	/// This may be absolutely standard and not special at all. I don't know, there were some differences between it and other CRC code I found in bizhawk
+	/// </summary>
+	public class SpecialCRC32
+	{
+		private static readonly uint[] CRC32Table;
+
+		static SpecialCRC32()
+		{
+			CRC32Table = new uint[256];
+			for (uint i = 0; i < 256; ++i)
+			{
+				uint crc = i;
+				for (int j = 8; j > 0; --j)
+				{
+					if ((crc & 1) == 1)
+						crc = ((crc >> 1) ^ 0xEDB88320);
+					else
+						crc >>= 1;
+				}
+				CRC32Table[i] = crc;
+			}
+		}
+
+		private uint current = 0xFFFFFFFF;
+
+		public void Add(ReadOnlySpan<byte> data)
+		{
+			foreach (var b in data) current = CRC32Table[(current ^ b) & 0xFF] ^ (current >> 8);
+		}
+
+		/// <summary>
+		/// The negated output (the typical result of the CRC calculation)
+		/// </summary>
+		public uint Result => current ^ 0xFFFFFFFF;
+
+		/// <summary>
+		/// The raw non-negated output
+		/// </summary>
+		public uint Current
+		{
+			get => current;
+			set => current = value;
+		}
+
+		private uint gf2_matrix_times(uint[] mat, uint vec)
+		{
+			int matIdx = 0;
+			uint sum = 0;
+			while (vec != 0)
+			{
+				if ((vec & 1) != 0)
+					sum ^= mat[matIdx];
+				vec >>= 1;
+				matIdx++;
+			}
+			return sum;
+		}
+
+		private void gf2_matrix_square(uint[] square, uint[] mat)
+		{
+			int n;
+			for (n = 0; n < 32; n++)
+				square[n] = gf2_matrix_times(mat, mat[n]);
+		}
+
+		/// <summary>
+		/// Incorporates a pre-calculated CRC with the given length by combining crcs
+		/// It's a bit flaky, so be careful, but it works
+		/// </summary>
+		public void Incorporate(uint crc, int len)
+		{
+			current = crc32_combine(current, crc, len);
+		}
+
+		//tables used by crc32_combine
+		private uint[] even, odd;
+
+		//algorithm from zlib's crc32_combine. read http://www.leapsecond.com/tools/crcomb.c for more
+		private uint crc32_combine(uint crc1, uint crc2, int len2)
+		{
+			even ??= new uint[32]; // even-power-of-two zeros operator
+			odd ??= new uint[32]; // odd-power-of-two zeros operator
+
+			// degenerate case
+			if (len2 == 0)
+				return crc1;
+
+			// put operator for one zero bit in odd
+			odd[0] = 0xedb88320;           //CRC-32 polynomial
+			uint row = 1;
+			for (int n = 1; n < 32; n++)
+			{
+				odd[n] = row;
+				row <<= 1;
+			}
+
+			//put operator for two zero bits in even
+			gf2_matrix_square(even, odd);
+
+			//put operator for four zero bits in odd
+			gf2_matrix_square(odd, even);
+
+			//apply len2 zeros to crc1 (first square will put the operator for one zero byte, eight zero bits, in even)
+			do
+			{
+				//apply zeros operator for this bit of len2
+				gf2_matrix_square(even, odd);
+				if ((len2 & 1) != 0)
+					crc1 = gf2_matrix_times(even, crc1);
+				len2 >>= 1;
+
+				//if no more bits set, then done
+				if (len2 == 0)
+					break;
+
+				//another iteration of the loop with odd and even swapped
+				gf2_matrix_square(odd, even);
+				if ((len2 & 1) != 0)
+					crc1 = gf2_matrix_times(odd, crc1);
+				len2 >>= 1;
+
+				//if no more bits set, then done
+			} while (len2 != 0);
+
+			//return combined crc
+			crc1 ^= crc2;
+			return crc1;
+		}
+	}
+}

src/BizHawk.Emulation.DiscSystem/DiscHasher.cs

@@ -1,5 +1,6 @@
 using System;
 
+using BizHawk.Common;
 using BizHawk.Common.BufferExtensions;
 
 namespace BizHawk.Emulation.DiscSystem
@@ -103,137 +104,5 @@ namespace BizHawk.Emulation.DiscSystem
 			}
 			return "no data track found";
 		}
-
-		/// <summary>
-		/// A stateful special CRC32 calculator
-		/// This may be absolutely standard and not special at all. I don't know, there were some differences between it and other CRC code I found in bizhawk
-		/// </summary>
-		public class SpecialCRC32
-		{
-			private static readonly uint[] CRC32Table;
-
-			static SpecialCRC32()
-			{
-				CRC32Table = new uint[256];
-				for (uint i = 0; i < 256; ++i)
-				{
-					uint crc = i;
-					for (int j = 8; j > 0; --j)
-					{
-						if ((crc & 1) == 1)
-							crc = ((crc >> 1) ^ 0xEDB88320);
-						else
-							crc >>= 1;
-					}
-					CRC32Table[i] = crc;
-				}
-			}
-
-			private uint current = 0xFFFFFFFF;
-
-			public void Add(ReadOnlySpan<byte> data)
-			{
-				foreach (var b in data) current = CRC32Table[(current ^ b) & 0xFF] ^ (current >> 8);
-			}
-
-			/// <summary>
-			/// The negated output (the typical result of the CRC calculation)
-			/// </summary>
-			public uint Result => current ^ 0xFFFFFFFF;
-
-			/// <summary>
-			/// The raw non-negated output
-			/// </summary>
-			public uint Current
-			{
-				get => current;
-				set => current = value;
-			}
-
-			private uint gf2_matrix_times(uint[] mat, uint vec)
-			{
-				int matIdx = 0;
-				uint sum = 0;
-				while (vec != 0)
-				{
-					if ((vec & 1) != 0)
-						sum ^= mat[matIdx];
-					vec >>= 1;
-					matIdx++;
-				}
-				return sum;
-			}
-
-			private void gf2_matrix_square(uint[] square, uint[] mat)
-			{
-				int n;
-				for (n = 0; n < 32; n++)
-					square[n] = gf2_matrix_times(mat, mat[n]);
-			}
-
-			/// <summary>
-			/// Incorporates a pre-calculated CRC with the given length by combining crcs
-			/// It's a bit flaky, so be careful, but it works
-			/// </summary>
-			public void Incorporate(uint crc, int len)
-			{
-				current = crc32_combine(current, crc, len);
-			}
-
-			//tables used by crc32_combine
-			private uint[] even, odd;
-
-			//algorithm from zlib's crc32_combine. read http://www.leapsecond.com/tools/crcomb.c for more
-			private uint crc32_combine(uint crc1, uint crc2, int len2)
-			{
-				even ??= new uint[32]; // even-power-of-two zeros operator
-				odd ??= new uint[32]; // odd-power-of-two zeros operator
-
-				// degenerate case
-				if (len2 == 0)
-					return crc1;
-
-				// put operator for one zero bit in odd
-				odd[0] = 0xedb88320;           //CRC-32 polynomial
-				uint row = 1;
-				for (int n = 1; n < 32; n++)
-				{
-					odd[n] = row;
-					row <<= 1;
-				}
-
-				//put operator for two zero bits in even
-				gf2_matrix_square(even, odd);
-
-				//put operator for four zero bits in odd
-				gf2_matrix_square(odd, even);
-
-				//apply len2 zeros to crc1 (first square will put the operator for one zero byte, eight zero bits, in even)
-				do
-				{
-					//apply zeros operator for this bit of len2
-					gf2_matrix_square(even, odd);
-					if ((len2 & 1) != 0)
-						crc1 = gf2_matrix_times(even, crc1);
-					len2 >>= 1;
-
-					//if no more bits set, then done
-					if (len2 == 0)
-						break;
-
-					//another iteration of the loop with odd and even swapped
-					gf2_matrix_square(odd, even);
-					if ((len2 & 1) != 0)
-						crc1 = gf2_matrix_times(odd, crc1);
-					len2 >>= 1;
-
-					//if no more bits set, then done
-				} while (len2 != 0);
-
-				//return combined crc
-				crc1 ^= crc2;
-				return crc1;
-			}
-		}
 	}
 }

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

@@ -1,5 +1,4 @@
 using BizHawk.Common;
-using BizHawk.Emulation.DiscSystem;
 
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
@@ -34,12 +33,12 @@ namespace BizHawk.Tests.Common.checksums
 			Assert.AreEqual(EXPECTED, CRC32.Calculate(data));
 
 			data = InitialiseArray();
-			DiscHasher.SpecialCRC32 crc32 = new();
+			SpecialCRC32 crc32 = new();
 			crc32.Add(data);
 			Assert.AreEqual(EXPECTED, crc32.Result);
 
 			var dataExtra = InitialiseArrayExtra();
-			DiscHasher.SpecialCRC32 crc32Extra = new();
+			SpecialCRC32 crc32Extra = new();
 			crc32Extra.Add(dataExtra);
 			Assert.AreEqual(EXPECTED_EXTRA, crc32Extra.Result);
 			crc32.Incorporate(crc32Extra.Result, dataExtra.Length);