diff --git a/src/BizHawk.Common/checksums/CRC32.cs b/src/BizHawk.Common/checksums/CRC32.cs
index 7d7516a2b1..df0f111674 100644
--- a/src/BizHawk.Common/checksums/CRC32.cs
+++ b/src/BizHawk.Common/checksums/CRC32.cs
@@ -1,46 +1,134 @@
-using System;
-
-namespace BizHawk.Common
-{
- // we could get a little list of crcs from here and make it clear which crc this class was for, and expose others
- // http://www.ross.net/crc/download/crc_v3.txt
- // TODO - why am I here? put me alongside hash_md5 and such
- public static class CRC32
- {
- // Lookup table for speed.
- private static readonly uint[] Crc32Table;
-
- static CRC32()
- {
- 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;
- }
- }
-
- public static uint Calculate(ReadOnlySpan<byte> data)
- {
- uint result = 0xFFFFFFFF;
- foreach (var b in data)
- {
- result = (result >> 8) ^ Crc32Table[b ^ (result & 0xFF)];
- }
-
- return ~result;
- }
- }
-}
+using System;
+
+namespace BizHawk.Common
+{
+ /// <remarks>Implementation of CRC-32 (i.e. POSIX cksum), intended for comparing discs against the Redump.org database</remarks>
+ public sealed class CRC32
+ {
+ /// <remarks>coefficients of the polynomial, in the format Wikipedia calls "reversed"</remarks>
+ public const uint POLYNOMIAL_CONST = 0xEDB88320U;
+
+ private static readonly uint[] COMBINER_INIT_STATE;
+
+ private static readonly uint[] CRC32Table;
+
+ static CRC32()
+ {
+ // for Add (CRC32 computation):
+ CRC32Table = new uint[256];
+ for (var i = 0U; i < 256U; i++)
+ {
+ var crc = i;
+ for (var j = 0; j < 8; j++)
+ {
+ var xor = (crc & 1U) == 1U;
+ crc >>= 1;
+ if (xor) crc ^= POLYNOMIAL_CONST;
+ }
+ CRC32Table[i] = crc;
+ }
+
+ // for Incorporate:
+ var combinerState = (COMBINER_INIT_STATE = new uint[64]).AsSpan();
+ var even = combinerState.Slice(start: 0, length: 32); // even-power-of-two zeros operator
+ var odd = combinerState.Slice(start: 32, length: 32); // odd-power-of-two zeros operator
+ // put operator for one zero bit in odd
+ odd[0] = POLYNOMIAL_CONST;
+ var oddTail = odd.Slice(1);
+ for (var n = 0; n < oddTail.Length; n++) oddTail[n] = 1U << n;
+ // 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);
+ }
+
+ public static uint Calculate(ReadOnlySpan<byte> data)
+ {
+ CRC32 crc32 = new();
+ crc32.Add(data);
+ return crc32.Result;
+ }
+
+ private static void gf2_matrix_square(Span<uint> square, ReadOnlySpan<uint> mat)
+ {
+ if (mat.Length != square.Length) throw new ArgumentException();
+ for (var n = 0; n < square.Length; n++) square[n] = gf2_matrix_times(mat, mat[n]);
+ }
+
+ private static uint gf2_matrix_times(ReadOnlySpan<uint> mat, uint vec)
+ {
+ var matIdx = 0;
+ uint sum = 0U;
+ while (vec != 0U)
+ {
+ if ((vec & 1U) != 0U) sum ^= mat[matIdx];
+ vec >>= 1;
+ matIdx++;
+ }
+ return sum;
+ }
+
+ private uint _current = 0xFFFFFFFFU;
+
+ /// <summary>The raw non-negated output</summary>
+ public uint Current
+ {
+ get => _current;
+ set => _current = value;
+ }
+
+ /// <summary>The negated output (the typical result of the CRC calculation)</summary>
+ public uint Result => ~_current;
+
+ public void Add(byte datum)
+ {
+ _current = CRC32Table[(_current ^ datum) & 0xFF] ^ (_current >> 8);
+ }
+
+ public void Add(ReadOnlySpan<byte> data)
+ {
+ foreach (var b in data)
+ {
+// Add(b); // I assume this would be slower
+ _current = CRC32Table[(_current ^ b) & 0xFF] ^ (_current >> 8);
+ }
+ }
+
+ /// <summary>
+ /// Incorporates a pre-calculated CRC with the given length by combining crcs<br/>
+ /// It's a bit flaky, so be careful, but it works
+ /// </summary>
+ /// <remarks>algorithm from zlib's crc32_combine. read http://www.leapsecond.com/tools/crcomb.c for more</remarks>
+ public void Incorporate(uint crc, int len)
+ {
+ if (len == 0) return; // degenerate case
+
+ Span<uint> combinerState = stackalloc uint[64];
+ COMBINER_INIT_STATE.CopyTo(combinerState);
+ var even = combinerState.Slice(start: 0, length: 32);
+ var odd = combinerState.Slice(start: 32, length: 32);
+
+ // apply len 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 len
+ gf2_matrix_square(even, odd);
+ if ((len & 1U) != 0U) _current = gf2_matrix_times(even, _current);
+ len >>= 1;
+
+ // if no more bits set, then done
+ if (len == 0U) break;
+
+ // another iteration of the loop with odd and even swapped
+ gf2_matrix_square(odd, even);
+ if ((len & 1U) != 0U) _current = gf2_matrix_times(odd, _current);
+ len >>= 1;
+
+ // if no more bits set, then done
+ } while (len != 0U);
+
+ // finally, combine and return
+ _current ^= crc;
+ }
+ }
+}
diff --git a/src/BizHawk.Common/checksums/SpecialCRC32.cs b/src/BizHawk.Common/checksums/SpecialCRC32.cs
deleted file mode 100644
index 57a82d3ee6..0000000000
--- a/src/BizHawk.Common/checksums/SpecialCRC32.cs
+++ /dev/null
@@ -1,138 +0,0 @@
-#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;
- }
- }
-}
diff --git a/src/BizHawk.Emulation.DiscSystem/DiscHasher.cs b/src/BizHawk.Emulation.DiscSystem/DiscHasher.cs
index 022ee45dc5..8a108d40ed 100644
--- a/src/BizHawk.Emulation.DiscSystem/DiscHasher.cs
+++ b/src/BizHawk.Emulation.DiscSystem/DiscHasher.cs
@@ -24,10 +24,8 @@ namespace BizHawk.Emulation.DiscSystem
//Tekken 3 (Europe) (Alt) and Tekken 3 (Europe) conflict in track 2 and 3 unfortunately, not sure what to do about this yet
//the TOC isn't needed!
//but it will help detect dumps with mangled TOCs which are all too common
- //
- //a possibly special CRC32 is used to help us match redump's DB elsewhere
- SpecialCRC32 crc = new SpecialCRC32();
+ CRC32 crc = new();
byte[] buffer2352 = new byte[2352];
var dsr = new DiscSectorReader(disc)
@@ -36,7 +34,7 @@ namespace BizHawk.Emulation.DiscSystem
};
//hash the TOC
- static void AddAsBytesTo(SpecialCRC32 crc32, int i)
+ static void AddAsBytesTo(CRC32 crc32, int i)
=> crc32.Add(BitConverter.GetBytes(i));
AddAsBytesTo(crc, (int)disc.TOC.Session1Format);
AddAsBytesTo(crc, disc.TOC.FirstRecordedTrackNumber);
@@ -64,8 +62,7 @@ namespace BizHawk.Emulation.DiscSystem
/// </summary>
public uint Calculate_PSX_RedumpHash()
{
- //a special CRC32 is used to help us match redump's DB
- SpecialCRC32 crc = new SpecialCRC32();
+ CRC32 crc = new();
byte[] buffer2352 = new byte[2352];
var dsr = new DiscSectorReader(disc)
diff --git a/src/BizHawk.Tests/Common/checksums/CRC32Tests.cs b/src/BizHawk.Tests/Common/checksums/CRC32Tests.cs
index 7994719054..734c3d7912 100644
--- a/src/BizHawk.Tests/Common/checksums/CRC32Tests.cs
+++ b/src/BizHawk.Tests/Common/checksums/CRC32Tests.cs
@@ -33,12 +33,12 @@ namespace BizHawk.Tests.Common.checksums
Assert.AreEqual(EXPECTED, CRC32.Calculate(data));
data = InitialiseArray();
- SpecialCRC32 crc32 = new();
+ CRC32 crc32 = new();
crc32.Add(data);
Assert.AreEqual(EXPECTED, crc32.Result);
var dataExtra = InitialiseArrayExtra();
- SpecialCRC32 crc32Extra = new();
+ CRC32 crc32Extra = new();
crc32Extra.Add(dataExtra);
Assert.AreEqual(EXPECTED_EXTRA, crc32Extra.Result);
crc32.Incorporate(crc32Extra.Result, dataExtra.Length);