Minor Optimization for DeflaterEngine and WuQuantizer

src/ImageSharp/Compression/Zlib/DeflaterEngine.cs

@@ -486,15 +486,16 @@ namespace SixLabors.ImageSharp.Compression.Zlib
             this.matchLen = Math.Max(this.matchLen, DeflaterConstants.MIN_MATCH - 1);
             int matchLength = this.matchLen;
 
-            if (scan + matchLength > scanMax)
+            int scanEndPosition = scan + matchLength;
+            if (scanEndPosition > scanMax)
             {
                 return false;
             }
 
             byte* pinnedWindow = this.pinnedWindowPointer;
             int scanStart = this.strstart;
-            byte scanEnd1 = pinnedWindow[scan + matchLength - 1];
-            byte scanEnd = pinnedWindow[scan + matchLength];
+            byte scanEnd1 = pinnedWindow[scanEndPosition - 1];
+            byte scanEnd = pinnedWindow[scanEndPosition];
 
             // Do not waste too much time if we already have a good match:
             if (matchLength >= this.goodLength)
@@ -508,8 +509,9 @@ namespace SixLabors.ImageSharp.Compression.Zlib
                 match = curMatch;
                 scan = scanStart;
 
-                if (pinnedWindow[match + matchLength] != scanEnd
-                 || pinnedWindow[match + matchLength - 1] != scanEnd1
+                int matchEndPosition = match + matchLength;
+                if (pinnedWindow[matchEndPosition] != scanEnd
+                 || pinnedWindow[matchEndPosition - 1] != scanEnd1
                  || pinnedWindow[match] != pinnedWindow[scan]
                  || pinnedWindow[++match] != pinnedWindow[++scan])
                 {
@@ -685,6 +687,7 @@ namespace SixLabors.ImageSharp.Compression.Zlib
                 return false;
             }
 
+            const int windowLen = (2 * DeflaterConstants.WSIZE) - DeflaterConstants.MIN_LOOKAHEAD;
             while (this.lookahead >= DeflaterConstants.MIN_LOOKAHEAD || flush)
             {
                 if (this.lookahead == 0)
@@ -695,7 +698,7 @@ namespace SixLabors.ImageSharp.Compression.Zlib
                     return false;
                 }
 
-                if (this.strstart > (2 * DeflaterConstants.WSIZE) - DeflaterConstants.MIN_LOOKAHEAD)
+                if (this.strstart > windowLen)
                 {
                     // slide window, as FindLongestMatch needs this.
                     // This should only happen when flushing and the window
@@ -766,6 +769,7 @@ namespace SixLabors.ImageSharp.Compression.Zlib
                 return false;
             }
 
+            const int windowLen = (2 * DeflaterConstants.WSIZE) - DeflaterConstants.MIN_LOOKAHEAD;
             while (this.lookahead >= DeflaterConstants.MIN_LOOKAHEAD || flush)
             {
                 if (this.lookahead == 0)
@@ -783,7 +787,7 @@ namespace SixLabors.ImageSharp.Compression.Zlib
                     return false;
                 }
 
-                if (this.strstart >= (2 * DeflaterConstants.WSIZE) - DeflaterConstants.MIN_LOOKAHEAD)
+                if (this.strstart >= windowLen)
                 {
                     // slide window, as FindLongestMatch needs this.
                     // This should only happen when flushing and the window

src/ImageSharp/Processing/Processors/Quantization/WuQuantizer{TPixel}.cs

@@ -176,9 +176,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             Rgba32 rgba = default;
             color.ToRgba32(ref rgba);
 
-            int r = rgba.R >> (8 - IndexBits);
-            int g = rgba.G >> (8 - IndexBits);
-            int b = rgba.B >> (8 - IndexBits);
+            const int shift = 8 - IndexBits;
+            int r = rgba.R >> shift;
+            int g = rgba.G >> shift;
+            int b = rgba.B >> shift;
             int a = rgba.A >> (8 - IndexAlphaBits);
 
             ReadOnlySpan<byte> tagSpan = this.tagsOwner.GetSpan();
@@ -413,6 +414,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
             Span<Moment> momentSpan = this.momentsOwner.GetSpan();
             Span<Moment> volumeSpan = volume.GetSpan();
             Span<Moment> areaSpan = area.GetSpan();
+            const int indexBits2 = IndexBits * 2;
+            const int indexAndAlphaBits = IndexBits + IndexAlphaBits;
+            const int indexBitsAndAlphaBits1 = IndexBits + IndexAlphaBits + 1;
             int baseIndex = GetPaletteIndex(1, 0, 0, 0);
 
             for (int r = 1; r < IndexCount; r++)
@@ -421,9 +425,9 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 // immediate outer loop. See https://github.com/dotnet/runtime/issues/61420
                 // To ensure the calculation doesn't happen repeatedly, hoist some of the calculations
                 // in the form of ind1* manually.
-                int ind1R = (r << ((IndexBits * 2) + IndexAlphaBits)) +
-                    (r << (IndexBits + IndexAlphaBits + 1)) +
-                    (r << (IndexBits * 2)) +
+                int ind1R = (r << (indexBits2 + IndexAlphaBits)) +
+                    (r << indexBitsAndAlphaBits1) +
+                    (r << indexBits2) +
                     (r << (IndexBits + 1)) +
                     r;
 
@@ -432,7 +436,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                 for (int g = 1; g < IndexCount; g++)
                 {
                     int ind1G = ind1R +
-                        (g << (IndexBits + IndexAlphaBits)) +
+                        (g << indexAndAlphaBits) +
                         (g << IndexBits) +
                         g;
                     int r_g = r + g;
@@ -446,7 +450,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
                             b;
 
                         Moment line = default;
-
+                        int bIndexAlphaOffset = b * IndexAlphaCount;
                         for (int a = 1; a < IndexAlphaCount; a++)
                         {
                             int ind1 = ind1B + a;
@@ -455,7 +459,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Quantization
 
                             areaSpan[a] += line;
 
-                            int inv = (b * IndexAlphaCount) + a;
+                            int inv = bIndexAlphaOffset + a;
                             volumeSpan[inv] += areaSpan[a];
 
                             int ind2 = ind1 - baseIndex;