Bit getting and setting methods

src/ImageSharp/Formats/Heif/Av1/Av1Math.cs

@@ -196,4 +196,10 @@ internal static class Av1Math
     /// <paramref name="a"/> implies <paramref name="b"/>.
     /// </summary>
     internal static bool Implies(bool a, bool b) => !a || b;
+
+    internal static int GetBit(int value, int n)
+        => (value & (1 << n)) >> n;
+
+    internal static void SetBit(ref int endOfBlockExtra, int n)
+        => endOfBlockExtra |= 1 << n;
 }

src/ImageSharp/Formats/Heif/Av1/Entropy/Av1SymbolDecoder.cs

@@ -353,7 +353,7 @@ internal ref struct Av1SymbolDecoder
             bool bit = this.ReadEndOfBlockExtra(transformSizeContext, planeType, endOfBlockContext);
             if (bit)
             {
-                endOfBlockExtra += 1 << (endOfBlockShift - 1);
+                Av1Math.SetBit(ref endOfBlockExtra, endOfBlockShift - 1);
             }
             else
             {
@@ -361,7 +361,7 @@ internal ref struct Av1SymbolDecoder
                 {
                     if (this.ReadLiteral(1) != 0)
                     {
-                        endOfBlockExtra += 1 << (endOfBlockShift - 1 - j);
+                        Av1Math.SetBit(ref endOfBlockExtra, endOfBlockShift - 1 - j);
                     }
                 }
             }
@@ -379,11 +379,11 @@ internal ref struct Av1SymbolDecoder
         if (level > Av1Constants.BaseLevelsCount)
         {
             int baseRangeContext = Av1SymbolContextHelper.GetBaseRangeContextEndOfBlock(position, transformClass);
-            for (int idx = 0; idx < Av1Constants.CoefficientBaseRange / Av1Constants.BaseRangeSizeMinus1; idx++)
+            for (int idx = 0; idx < Av1Constants.CoefficientBaseRange; idx += Av1Constants.BaseRangeSizeMinus1)
             {
-                int coefficinetBaseRange = this.ReadCoefficientsBaseRange(transformSizeContext, planeType, baseRangeContext);
-                level += coefficinetBaseRange;
-                if (coefficinetBaseRange < Av1Constants.BaseRangeSizeMinus1)
+                int coefficientBaseRange = this.ReadCoefficientsBaseRange(transformSizeContext, planeType, baseRangeContext);
+                level += coefficientBaseRange;
+                if (coefficientBaseRange < Av1Constants.BaseRangeSizeMinus1)
                 {
                     break;
                 }
@@ -405,9 +405,9 @@ internal ref struct Av1SymbolDecoder
                 int baseRangeContext = Av1SymbolContextHelper.GetBaseRangeContext2d(levels, position);
                 for (int idx = 0; idx < Av1Constants.CoefficientBaseRange; idx += Av1Constants.BaseRangeSizeMinus1)
                 {
-                    int k = this.ReadCoefficientsBaseRange(transformSizeContext, planeType, baseRangeContext);
-                    level += k;
-                    if (k < Av1Constants.BaseRangeSizeMinus1)
+                    int coefficientBaseRange = this.ReadCoefficientsBaseRange(transformSizeContext, planeType, baseRangeContext);
+                    level += coefficientBaseRange;
+                    if (coefficientBaseRange < Av1Constants.BaseRangeSizeMinus1)
                     {
                         break;
                     }

src/ImageSharp/Formats/Heif/Av1/Entropy/Av1SymbolEncoder.cs

@@ -204,13 +204,13 @@ internal class Av1SymbolEncoder : IDisposable
         {
             ref Av1SymbolWriter w = ref this.writer;
             int eobShift = eobOffsetBitCount - 1;
-            uint bit = (eobExtra & (1 << eobShift)) != 0 ? 1u : 0u;
-            w.WriteSymbol((int)bit, this.endOfBlockExtra[(int)transformSizeContext][(int)componentType][endOfBlockPosition]);
+            int bit = Av1Math.GetBit(eobExtra, eobShift);
+            w.WriteSymbol(bit, this.endOfBlockExtra[(int)transformSizeContext][(int)componentType][endOfBlockPosition]);
             for (int i = 1; i < eobOffsetBitCount; i++)
             {
                 eobShift = eobOffsetBitCount - 1 - i;
-                bit = (eobExtra & (1 << eobShift)) != 0 ? 1u : 0u;
-                w.WriteLiteral(bit, 1);
+                bit = Av1Math.GetBit(eobExtra, eobShift);
+                w.WriteLiteral((uint)bit, 1);
             }
         }
     }

tests/ImageSharp.Tests/Formats/Heif/Av1/Av1MathTests.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Heif.Av1;
+
+namespace SixLabors.ImageSharp.Tests.Formats.Heif.Av1;
+
+[Trait("Format", "Avif")]
+public class Av1MathTests
+{
+    [Theory]
+    [InlineData(4, 2, 1)]
+    [InlineData(4, 3, 0)]
+    [InlineData(5, 3, 0)]
+    [InlineData(8, 3, 1)]
+    [InlineData(9, 3, 1)]
+    [InlineData(9, 0, 1)]
+    [InlineData(8, 0, 0)]
+    public void TestGetBitSet(int value, int n, int expected)
+    {
+        int actual = Av1Math.GetBit(value, n);
+        Assert.Equal(expected, actual);
+    }
+
+    [Theory]
+    [InlineData(4, 2, 4)]
+    [InlineData(0, 2, 4)]
+    [InlineData(0, 3, 8)]
+    [InlineData(4, 3, 12)]
+    public void TestSetBitSet(int value, int n, int expected)
+    {
+        int actual = value;
+        Av1Math.SetBit(ref actual, n);
+        Assert.Equal(expected, actual);
+    }
+}