Symbol context test

src/ImageSharp/Formats/Heif/Av1/Entropy/Av1SymbolContextHelper.cs

@@ -108,29 +108,6 @@ internal static class Av1SymbolContextHelper
         return 3;
     }
 
-    /// <summary>
-    /// SVT: get_lower_levels_ctx_eob
-    /// </summary>
-    internal static int GetLowerLevelContextEndOfBlock(int blockWidthLog2, int height, int scanIndex)
-    {
-        if (scanIndex == 0)
-        {
-            return 0;
-        }
-
-        if (scanIndex <= height << blockWidthLog2 >> 3)
-        {
-            return 1;
-        }
-
-        if (scanIndex <= height << blockWidthLog2 >> 2)
-        {
-            return 2;
-        }
-
-        return 3;
-    }
-
     /// <summary>
     /// SVT: get_br_ctx_2d
     /// </summary>

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1SymbolContextTests.cs

@@ -0,0 +1,71 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Heif.Av1;
+using SixLabors.ImageSharp.Formats.Heif.Av1.Entropy;
+using SixLabors.ImageSharp.Formats.Heif.Av1.Tiling;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Heif.Av1;
+
+[Trait("Format", "Avif")]
+public class Av1SymbolContextTests
+{
+    [Theory]
+    [MemberData(nameof(GetCombinations))]
+    public void TestAccuracy(int width, int height, int index)
+    {
+        // Arrange
+        Size size = new(width, height);
+        Av1LevelBuffer levels = new(Configuration.Default, size);
+        Point position = levels.GetPosition(index);
+        int blockWidthLog2 = Av1Math.Log2(width);
+        int expectedContext = GetExpectedLowerLevelContextEndOfBlock(blockWidthLog2, height, index);
+
+        // Act
+        int actualContext = Av1SymbolContextHelper.GetLowerLevelContextEndOfBlock(levels, position);
+
+        // Assert
+        Assert.Equal(expectedContext, actualContext);
+    }
+
+    public static TheoryData<int, int, int> GetCombinations()
+    {
+        TheoryData<int, int, int> result = [];
+        for (int y = 1; y < 6; y++)
+        {
+            for (int x = 1; x < 6; x++)
+            {
+                int total = (1 << x) * (1 << y);
+                for (int i = 0; i < total; i++)
+                {
+                    result.Add(1 << x, 1 << y, i);
+                }
+            }
+        }
+
+        return result;
+    }
+
+    /// <summary>
+    /// SVT: get_lower_levels_ctx_eob
+    /// </summary>
+    internal static int GetExpectedLowerLevelContextEndOfBlock(int blockWidthLog2, int height, int scanIndex)
+    {
+        if (scanIndex == 0)
+        {
+            return 0;
+        }
+
+        if (scanIndex <= height << blockWidthLog2 >> 3)
+        {
+            return 1;
+        }
+
+        if (scanIndex <= height << blockWidthLog2 >> 2)
+        {
+            return 2;
+        }
+
+        return 3;
+    }
+}