From 4c14c57d09aa9d115cf881cafef5f70ba99c035c Mon Sep 17 00:00:00 2001
From: Dmitry Pentin <riotbr3aker@gmail.com>
Date: Wed, 18 Aug 2021 15:11:15 +0300
Subject: [PATCH] Greatly reduced operations per emit call

---
 .../Jpeg/Components/Encoder/HuffmanLut.cs     |  3 ++-
 .../Components/Encoder/HuffmanScanEncoder.cs  | 23 ++++++++-----------
 2 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanLut.cs b/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanLut.cs
index ec77bf87db..f563e74e09 100644
--- a/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanLut.cs
+++ b/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanLut.cs
@@ -4,6 +4,7 @@
 namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
 {
     /// <summary>
+    /// TODO: THIS IS NO LONGER TRUE, INTERNAL REPRESENTATION WAS CHANGED AND THIS DOC SHOULD BE CHANGED TOO!!!
     /// A compiled look-up table representation of a huffmanSpec.
     /// Each value maps to a int32 of which the 24 most significant bits hold the
     /// codeword in bits and the 8 least significant bits hold the codeword size.
@@ -54,7 +55,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
                 int len = i + 1;
                 for (int j = 0; j < spec.Count[i]; j++)
                 {
-                    this.Values[spec.Values[k]] = len | (code << 8);
+                    this.Values[spec.Values[k]] = len | (code << (32 - len));
                     code++;
                     k++;
                 }
diff --git a/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanScanEncoder.cs b/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanScanEncoder.cs
index 42a683539d..fba814882b 100644
--- a/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanScanEncoder.cs
+++ b/src/ImageSharp/Formats/Jpeg/Components/Encoder/HuffmanScanEncoder.cs
@@ -349,16 +349,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
         [MethodImpl(InliningOptions.ShortMethod)]
         private void Emit(uint bits, int count)
         {
-            uint correctedBits = bits << (32 - count);
-
-            this.accumulatedBits |= correctedBits >> this.bitCount;
+            this.accumulatedBits |= bits >> this.bitCount;
 
             count += this.bitCount;
 
             if (count >= 32)
             {
                 this.emitBuffer[--this.emitWriteIndex] = this.accumulatedBits;
-                this.accumulatedBits = correctedBits << (32 - this.bitCount);
+                this.accumulatedBits = bits << (32 - this.bitCount);
 
                 count -= 32;
             }
@@ -375,7 +373,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
         private void EmitHuff(int[] table, int value)
         {
             int x = table[value];
-            this.Emit((uint)x >> 8, x & 0xff);
+            this.Emit((uint)x & 0xffff_ff00u, x & 0xff);
         }
 
         [MethodImpl(InliningOptions.ShortMethod)]
@@ -389,13 +387,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
                 b = value - 1;
             }
 
-            int bt = GetHuffmanEncodingLength((uint)a);
+            int valueLen = GetHuffmanEncodingLength((uint)a);
 
-            this.EmitHuff(table, bt);
-            if (bt > 0)
-            {
-                this.Emit((uint)(b & ((1 << bt) - 1)), bt);
-            }
+            this.EmitHuff(table, valueLen);
+            this.Emit((uint)b << (32 - valueLen), valueLen);
         }
 
         /// <summary>
@@ -415,10 +410,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
                 b = value - 1;
             }
 
-            int bt = GetHuffmanEncodingLength((uint)a);
+            int valueLen = GetHuffmanEncodingLength((uint)a);
 
-            this.EmitHuff(table, (runLength << 4) | bt);
-            this.Emit((uint)(b & ((1 << bt) - 1)), bt);
+            this.EmitHuff(table, (runLength << 4) | valueLen);
+            this.Emit((uint)b << (32 - valueLen), valueLen);
         }
 
         /// <summary>