Add test for calculating residual costs

src/ImageSharp/Formats/Webp/Lossy/Vp8Residual.cs

@@ -173,55 +173,6 @@ internal class Vp8Residual
             return LossyUtils.Vp8BitCost(0, (byte)p0);
         }
 
-        if (false)
-        {
-            Span<byte> scratch = stackalloc byte[32];
-            Span<byte> ctxs = scratch.Slice(0, 16);
-            Span<byte> levels = scratch.Slice(16);
-            Span<ushort> absLevels = stackalloc ushort[16];
-
-            // Precompute clamped levels and contexts, packed to 8b.
-            ref short outputRef = ref MemoryMarshal.GetReference<short>(this.Coeffs);
-            Vector256<short> c0 = Unsafe.As<short, Vector256<byte>>(ref outputRef).AsInt16();
-            Vector256<short> d0 = Avx2.Subtract(Vector256<short>.Zero, c0);
-            Vector256<short> e0 = Avx2.Max(c0, d0); // abs(v), 16b
-            Vector256<sbyte> f = Avx2.PackSignedSaturate(e0, e0);
-            Vector256<byte> g = Avx2.Min(f.AsByte(), Vector256.Create((byte)2));
-            Vector256<byte> h = Avx2.Min(f.AsByte(), Vector256.Create((byte)67)); // clampLevel in [0..67]
-
-            ref byte ctxsRef = ref MemoryMarshal.GetReference(ctxs);
-            ref byte levelsRef = ref MemoryMarshal.GetReference(levels);
-            ref ushort absLevelsRef = ref MemoryMarshal.GetReference(absLevels);
-            Unsafe.As<byte, Vector128<byte>>(ref ctxsRef) = g.GetLower();
-            Unsafe.As<byte, Vector128<byte>>(ref levelsRef) = h.GetLower();
-            Unsafe.As<ushort, Vector256<ushort>>(ref absLevelsRef) = e0.AsUInt16();
-
-            int level;
-            int flevel;
-            for (; n < this.Last; ++n)
-            {
-                int ctx = ctxs[n];
-                level = levels[n];
-                flevel = absLevels[n];
-                cost += WebpLookupTables.Vp8LevelFixedCosts[flevel] + t.Costs[level];
-                t = costs[n + 1].Costs[ctx];
-            }
-
-            // Last coefficient is always non-zero.
-            level = levels[n];
-            flevel = absLevels[n];
-            cost += WebpLookupTables.Vp8LevelFixedCosts[flevel] + t.Costs[level];
-            if (n < 15)
-            {
-                int b = WebpConstants.Vp8EncBands[n + 1];
-                int ctx = ctxs[n];
-                int lastP0 = this.Prob[b].Probabilities[ctx].Probabilities[0];
-                cost += LossyUtils.Vp8BitCost(0, (byte)lastP0);
-            }
-
-            return cost;
-        }
-
         if (Sse2.IsSupported)
         {
             Span<byte> scratch = stackalloc byte[32];

tests/ImageSharp.Tests/Formats/WebP/Vp8ResidualTests.cs

@@ -11,6 +11,22 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp;
 [Trait("Format", "Webp")]
 public class Vp8ResidualTests
 {
+    [Fact]
+    public void GetResidualCost_Works()
+    {
+        // arrange
+        int ctx0 = 0;
+        int expected = 20911;
+        string jsonString = File.ReadAllText(@"TestDataWebp\Vp8Residual.json");
+        Vp8Residual residual = JsonSerializer.Deserialize<Vp8Residual>(jsonString);
+
+        // act
+        int actual = residual.GetResidualCost(ctx0);
+
+        // assert
+        Assert.Equal(expected, actual);
+    }
+
     [Fact]
     public void Serialization_Works()
     {

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -56,6 +56,9 @@
     <None Update="TestFonts\SixLaborsSampleAB.woff">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
+    <None Update="TestDataWebp\Vp8Residual.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
     <None Update="xunit.runner.json">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>