[WIP] outer scope memory propagation

src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs

@@ -728,10 +728,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <param name="codeLengths">Code lengths.</param>
         /// <param name="values">Code values.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public void BuildHuffmanTable(int type, int index, ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values)
+        public void BuildHuffmanTable(int type, int index, ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values, Span<uint> workspace)
         {
             HuffmanTable[] tables = type == 0 ? this.dcHuffmanTables : this.acHuffmanTables;
-            tables[index] = new HuffmanTable(codeLengths, values);
+            tables[index] = new HuffmanTable(codeLengths, values, workspace);
         }
     }
 }

src/ImageSharp/Formats/Jpeg/Components/Decoder/HuffmanTable.cs

@@ -51,13 +51,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <summary>
         /// Initializes a new instance of the <see cref="HuffmanTable"/> struct.
         /// </summary>
-        /// <param name="codeLengths">The code lengths</param>
-        /// <param name="values">The huffman values</param>
-        public HuffmanTable(ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values)
+        /// <param name="codeLengths">The code lengths.</param>
+        /// <param name="values">The huffman values.</param>
+        /// <param name="workspace">The spare workspace memory, must be provided by the caller.</param>
+        public HuffmanTable(ReadOnlySpan<byte> codeLengths, ReadOnlySpan<byte> values, Span<uint> workspace)
         {
             Unsafe.CopyBlockUnaligned(ref this.Values[0], ref MemoryMarshal.GetReference(values), (uint)values.Length);
 
-            Span<uint> huffCode = stackalloc uint[257];
+            Span<uint> huffCode = workspace;
 
             // Generate codes
             uint code = 0;

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -1150,7 +1150,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                                 tableType,
                                 tableIndex,
                                 codeLengthsSpan,
-                                huffmanValuesSpan);
+                                huffmanValuesSpan,
+                                stackalloc uint[257]);
                         }
                     }
                 }