Reduced memory pressure, removed unnecessary buffer

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -1095,12 +1095,15 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <param name="remaining">The remaining bytes in the segment block.</param>
         private void ProcessDefineHuffmanTablesMarker(BufferedReadStream stream, int remaining)
         {
-            int length = remaining;
+            const int codeLengthsByteSize = 16;
+            const int codeValuesMaxByteSize = 256;
+            const int tableWorkspaceByteSize = 257 * sizeof(uint);
+            const int totalBufferSize = codeLengthsByteSize + codeValuesMaxByteSize + tableWorkspaceByteSize;
 
-            using (IMemoryOwner<byte> huffmanData = this.Configuration.MemoryAllocator.Allocate<byte>(256, AllocationOptions.Clean))
+            int length = remaining;
+            using (IMemoryOwner<byte> huffmanData = this.Configuration.MemoryAllocator.Allocate<byte>(17))
             {
                 Span<byte> huffmanDataSpan = huffmanData.GetSpan();
-                ref byte huffmanDataRef = ref MemoryMarshal.GetReference(huffmanDataSpan);
                 for (int i = 2; i < remaining;)
                 {
                     byte huffmanTableSpec = (byte)stream.ReadByte();
@@ -1119,17 +1122,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                         JpegThrowHelper.ThrowInvalidImageContentException($"Bad huffman table index: {tableIndex}.");
                     }
 
-                    stream.Read(huffmanDataSpan, 0, 16);
+                    stream.Read(huffmanDataSpan, 1, 16);
 
-                    using (IMemoryOwner<byte> codeLengths = this.Configuration.MemoryAllocator.Allocate<byte>(17, AllocationOptions.Clean))
-                    {
-                        Span<byte> codeLengthsSpan = codeLengths.GetSpan();
-                        ref byte codeLengthsRef = ref MemoryMarshal.GetReference(codeLengthsSpan);
                     int codeLengthSum = 0;
-
                     for (int j = 1; j < 17; j++)
                     {
-                            codeLengthSum += Unsafe.Add(ref codeLengthsRef, j) = Unsafe.Add(ref huffmanDataRef, j - 1);
+                        codeLengthSum += huffmanDataSpan[j];
                     }
 
                     length -= 17;
@@ -1149,14 +1147,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                         this.scanDecoder.BuildHuffmanTable(
                             tableType,
                             tableIndex,
-                                codeLengthsSpan,
+                            huffmanDataSpan,
                             huffmanValuesSpan,
                             stackalloc uint[257]);
                     }
                 }
             }
         }
-        }
 
         /// <summary>
         /// Processes the DRI (Define Restart Interval Marker) Which specifies the interval between RSTn markers, in