Eliminate this = default shortcut when height * width = 0

Author: marcin-krystianc

src/CommunityToolkit.HighPerformance/Memory/Internals/OverflowHelper.cs

@@ -64,6 +64,9 @@ public static void EnsureIsInNativeIntRange(int height, int width, int pitch)
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static int ComputeInt32Area(int height, int width, int pitch)
     {
-        return checked(((width + pitch) * Max(unchecked(height - 1), 0)) + width);
+        if (height <= 0 || width <= 0)
+            return 0;
+
+        return checked(((width + pitch) * (height - 1)) + width);
     }
 }

src/CommunityToolkit.HighPerformance/Memory/Memory2D{T}.cs

@@ -362,13 +362,6 @@ public unsafe Memory2D(MemoryManager<T> memoryManager, int offset, int height, i
             ThrowHelper.ThrowArgumentOutOfRangeExceptionForPitch();
         }
 
-        if (width == 0 || height == 0)
-        {
-            this = default;
-
-            return;
-        }
-
         int area = OverflowHelper.ComputeInt32Area(height, width, pitch);
         int remaining = length - offset;
 
@@ -435,16 +428,8 @@ internal unsafe Memory2D(Memory<T> memory, int offset, int height, int width, in
             ThrowHelper.ThrowArgumentOutOfRangeExceptionForPitch();
         }
 
-        if (width == 0 || height == 0)
-        {
-            this = default;
-
-            return;
-        }
-
-        int
-            area = OverflowHelper.ComputeInt32Area(height, width, pitch),
-            remaining = memory.Length - offset;
+        int area = OverflowHelper.ComputeInt32Area(height, width, pitch);
+        int remaining = memory.Length - offset;
 
         if (area > remaining)
         {

src/CommunityToolkit.HighPerformance/Memory/ReadOnlyMemory2D{T}.cs

@@ -382,13 +382,6 @@ public unsafe ReadOnlyMemory2D(MemoryManager<T> memoryManager, int offset, int h
             ThrowHelper.ThrowArgumentOutOfRangeExceptionForPitch();
         }
 
-        if (width == 0 || height == 0)
-        {
-            this = default;
-
-            return;
-        }
-
         int area = OverflowHelper.ComputeInt32Area(height, width, pitch);
         int remaining = length - offset;
 
@@ -455,13 +448,6 @@ internal unsafe ReadOnlyMemory2D(ReadOnlyMemory<T> memory, int offset, int heigh
             ThrowHelper.ThrowArgumentOutOfRangeExceptionForPitch();
         }
 
-        if (width == 0 || height == 0)
-        {
-            this = default;
-
-            return;
-        }
-
         int area = OverflowHelper.ComputeInt32Area(height, width, pitch);
         int remaining = memory.Length - offset;
 

src/CommunityToolkit.HighPerformance/Memory/ReadOnlySpan2D{T}.cs

@@ -209,13 +209,6 @@ public ReadOnlySpan2D(T[] array, int offset, int height, int width, int pitch)
             ThrowHelper.ThrowArgumentOutOfRangeExceptionForPitch();
         }
 
-        if (width == 0 || height == 0)
-        {
-            this = default;
-
-            return;
-        }
-
         int area = OverflowHelper.ComputeInt32Area(height, width, pitch);
         int remaining = array.Length - offset;
 
@@ -459,13 +452,6 @@ internal ReadOnlySpan2D(ReadOnlySpan<T> span, int offset, int height, int width,
             ThrowHelper.ThrowArgumentOutOfRangeExceptionForPitch();
         }
 
-        if (width == 0 || height == 0)
-        {
-            this = default;
-
-            return;
-        }
-
         int area = OverflowHelper.ComputeInt32Area(height, width, pitch);
         int remaining = span.Length - offset;
 

src/CommunityToolkit.HighPerformance/Memory/Span2D{T}.cs

@@ -531,13 +531,6 @@ internal Span2D(Span<T> span, int offset, int height, int width, int pitch)
             ThrowHelper.ThrowArgumentOutOfRangeExceptionForPitch();
         }
 
-        if (width == 0 || height == 0)
-        {
-            this = default;
-
-            return;
-        }
-
         int area = OverflowHelper.ComputeInt32Area(height, width, pitch);
         int remaining = span.Length - offset;
 

tests/CommunityToolkit.HighPerformance.UnitTests/Extensions/Test_SpanExtensions.cs

@@ -199,4 +199,45 @@ public void Test_SpanExtensions_CopyTo_RefEnumerable()
 
         CollectionAssert.AreEqual(array, result);
     }
+
+#if NET6_0_OR_GREATER
+    [TestMethod]
+    public void Test_SpanExtensions_AsSpan2d_Empty()
+    {
+        Span2D<int> empty2 = Span<int>.Empty.AsSpan2D(0, 0);
+        Assert.IsTrue(empty2.IsEmpty);
+        Assert.AreEqual(empty2.Length, 0);
+        Assert.AreEqual(empty2.Width, 0);
+        Assert.AreEqual(empty2.Height, 0);
+
+        Span2D<int> empty3 = Span<int>.Empty.AsSpan2D(4, 0);
+        Assert.IsTrue(empty3.IsEmpty);
+        Assert.AreEqual(empty3.Length, 0);
+        Assert.AreEqual(empty3.Width, 0);
+        Assert.AreEqual(empty3.Height, 4);
+
+        Span2D<int> empty4 = Span<int>.Empty.AsSpan2D(0, 7);
+        Assert.IsTrue(empty4.IsEmpty);
+        Assert.AreEqual(empty4.Length, 0);
+        Assert.AreEqual(empty4.Width, 7);
+        Assert.AreEqual(empty4.Height, 0);
+    }
+
+    [TestMethod]
+    public void Test_SpanExtensions_AsSpan2d_Copy()
+    {
+        int[,] array = new int[2, 3];
+        int[] values1 = { 1, 2, 3, 4, 5, 6 };
+        // Copy a span to a target row and column with valid lengths
+        values1.AsSpan().AsSpan2D(2, 3).CopyTo(array);
+        int[,] result = new[,]
+        {
+            { 1, 2, 3 },
+            { 4, 5, 6 },
+        };
+
+        CollectionAssert.AreEqual(array, result);
+        _ = Assert.ThrowsException<ArgumentException>(() => values1.AsSpan().AsSpan2D(3, 2).CopyTo(array));
+    }
+#endif
 }