Add unit tests for Reed Solomon ECC encoding and correction

2026-07-08 18:16:24 +00:00 · 2026-04-09 18:18:23 +01:00
parent 97bf0913a7
commit e10f1fc873
1 changed files with 148 additions and 0 deletions
--- a/Aaru.Tests/Checksums/ReedSolomonTests.cs
+++ b/Aaru.Tests/Checksums/ReedSolomonTests.cs
@@ -0,0 +1,148 @@
+// /***************************************************************************
+// Aaru Data Preservation Suite
+// ----------------------------------------------------------------------------
+//
+// Filename       : ReedSolomonTests.cs
+// Author(s)      : Natalia Portillo <claunia@claunia.com>
+//
+// Component      : Aaru unit testing.
+//
+// --[ License ] --------------------------------------------------------------
+//
+//     This program is free software: you can redistribute it and/or modify
+//     it under the terms of the GNU General Public License as
+//     published by the Free Software Foundation, either version 3 of the
+//     License, or (at your option) any later version.
+//
+//     This program is distributed in the hope that it will be useful,
+//     but WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//     GNU General Public License for more details.
+//
+//     You should have received a copy of the GNU General Public License
+//     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// ----------------------------------------------------------------------------
+// Copyright © 2011-2026 Natalia Portillo
+// ****************************************************************************/
+
+using System;
+using Aaru.Checksums;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace Aaru.Tests.Checksums;
+
+[TestFixture]
+public class ReedSolomonTests
+{
+    [Test]
+    public void Mode1SectorEccPRowCanBeEncodedAndCorrected()
+    {
+        ReedSolomon reedSolomon = CreateCdReedSolomon();
+        int[]       row         = ExtractCdRow(CdChecksumsFix.Mode1Sector, 0, 86, 24, 2, 86, false);
+
+        VerifyCdRowRoundTrip(reedSolomon, row, 252, 0x55);
+    }
+
+    [Test]
+    public void Mode1SectorEccQRowCanBeEncodedAndCorrected()
+    {
+        ReedSolomon reedSolomon = CreateCdReedSolomon();
+        int[]       row         = ExtractCdRow(CdChecksumsFix.Mode1Sector, 0, 52, 43, 86, 88, false);
+
+        VerifyCdRowRoundTrip(reedSolomon, row, 251, 0xA5);
+    }
+
+    [Test]
+    public void Mode2Form1SectorEccPRowCanBeEncodedAndCorrected()
+    {
+        ReedSolomon reedSolomon = CreateCdReedSolomon();
+        int[]       row         = ExtractCdRow(CdChecksumsFix.Mode2Form1Sector, 0, 86, 24, 2, 86, true);
+
+        VerifyCdRowRoundTrip(reedSolomon, row, 252, 0x33);
+    }
+
+    [Test]
+    public void Mode2Form1SectorEccQRowCanBeEncodedAndCorrected()
+    {
+        ReedSolomon reedSolomon = CreateCdReedSolomon();
+        int[]       row         = ExtractCdRow(CdChecksumsFix.Mode2Form1Sector, 0, 52, 43, 86, 88, true);
+
+        VerifyCdRowRoundTrip(reedSolomon, row, 251, 0x77);
+    }
+
+    static ReedSolomon CreateCdReedSolomon()
+    {
+        ReedSolomon reedSolomon = new();
+        reedSolomon.InitRs(255, 253, 8);
+
+        return reedSolomon;
+    }
+
+    static void VerifyCdRowRoundTrip(ReedSolomon reedSolomon, int[] row, int errorIndex, int errorMask)
+    {
+        int[] data   = CreateShortenedData(row);
+        int   result = reedSolomon.encode_rs(data, out int[] parity);
+
+        result.Should().Be(0);
+
+        int[] codeword = BuildCodeword(data, parity);
+        var   expected = (int[])codeword.Clone();
+
+        int verifiedSymbols = reedSolomon.eras_dec_rs(ref codeword, out int[] verifiedErasures, 0);
+
+        verifiedSymbols.Should().Be(0);
+        codeword.Should().Equal(expected);
+        verifiedErasures.Should().NotBeNull();
+
+        var corruptedCodeword = (int[])expected.Clone();
+        corruptedCodeword[errorIndex] ^= errorMask;
+
+        int correctedSymbols = reedSolomon.eras_dec_rs(ref corruptedCodeword, out int[] erasPos, 0);
+
+        correctedSymbols.Should().Be(1);
+        corruptedCodeword.Should().Equal(expected);
+        erasPos.Should().NotBeNull();
+    }
+
+    static int[] ExtractCdRow(byte[] sector, int major, int majorCount, int minorCount, int majorMult, int minorInc,
+                              bool   zeroAddress)
+    {
+        var row   = new int[minorCount];
+        int size  = majorCount * minorCount;
+        int index = (major >> 1) * majorMult + (major & 1);
+
+        for(var minor = 0; minor < minorCount; minor++)
+        {
+            row[minor] = index < 4 && !zeroAddress
+                             ? sector[0x0C + index]
+                             : index < 4
+                                 ? 0
+                                 : sector[0x10 + index - 4];
+
+            index += minorInc;
+
+            if(index >= size) index -= size;
+        }
+
+        return row;
+    }
+
+    static int[] CreateShortenedData(int[] row)
+    {
+        var data = new int[253];
+        Array.Copy(row, 0, data, data.Length - row.Length, row.Length);
+
+        return data;
+    }
+
+    static int[] BuildCodeword(int[] data, int[] parity)
+    {
+        var codeword = new int[255];
+        Array.Copy(data,   0, codeword, 0,           data.Length);
+        Array.Copy(parity, 0, codeword, data.Length, parity.Length);
+
+        return codeword;
+    }
+}