Option #2 - use the default compression value (-1) for both Windows a…

…nd Unix. Since we are currently planning on moving to a newer zlib version on Windows, and considering how to not even ship our own zlib, we let the current zlib version pick the best compression level.
eerhardt · Nov 12, 2015 · 38883e3 · 38883e3
1 parent fc4ecdf
commit 38883e3
Showing 1 changed file with 11 additions and 20 deletions.
diff --git a/src/System.IO.Compression/src/System/IO/Compression/DeflaterZLib.cs b/src/System.IO.Compression/src/System/IO/Compression/DeflaterZLib.cs
@@ -27,7 +27,6 @@ internal class DeflaterZLib : IDeflater
         #region exposed members
 
         internal DeflaterZLib()
-
             : this(CompressionLevel.Optimal)
         {
         }
@@ -37,39 +36,31 @@ internal DeflaterZLib(CompressionLevel compressionLevel)
             ZLibNative.CompressionLevel zlibCompressionLevel;
             int windowBits;
             int memLevel;
-            ZLibNative.CompressionStrategy strategy;
+            ZLibNative.CompressionStrategy strategy = ZLibNative.CompressionStrategy.DefaultStrategy;
 
             switch (compressionLevel)
             {
-                // Note that ZLib currently exactly correspond to the optimal values.
-                // However, we have determined the optimal values by intependent measurements across
-                // a range of all possible ZLib parameters and over a set of different data.
-                // We stress that by using explicitly the values obtained by the measurements rather than
-                // ZLib defaults even if they happened to be the same.
-                // For ZLib 1.2.3 we have (copied from ZLibNative.cs):
-                // ZLibNative.CompressionLevel.DefaultCompression = 6;
-                // ZLibNative.Deflate_DefaultWindowBits = -15;
-                // ZLibNative.Deflate_DefaultMemLevel = 8;
+                // Since we don't know exactly which version of ZLib will be used on the machine,
+                // we use the ZLib DefaultCompression level for CompressionLevel.Optimal.
+                // This allows the current ZLib library to decide which level is the best to use.
+                // See the note in ZLibNative.CompressionLevel for the recommended combinations.
 
                 case CompressionLevel.Optimal:
-                    zlibCompressionLevel = (ZLibNative.CompressionLevel)6;
-                    windowBits = -15;
-                    memLevel = 8;
-                    strategy = ZLibNative.CompressionStrategy.DefaultStrategy;
+                    zlibCompressionLevel = ZLibNative.CompressionLevel.DefaultCompression;
+                    windowBits = ZLibNative.Deflate_DefaultWindowBits;
+                    memLevel = ZLibNative.Deflate_DefaultMemLevel;
                     break;
 
                 case CompressionLevel.Fastest:
                     zlibCompressionLevel = ZLibNative.CompressionLevel.BestSpeed;
-                    windowBits = -15;
-                    memLevel = 8;
-                    strategy = ZLibNative.CompressionStrategy.DefaultStrategy;
+                    windowBits = ZLibNative.Deflate_DefaultWindowBits;
+                    memLevel = ZLibNative.Deflate_DefaultMemLevel;
                     break;
 
                 case CompressionLevel.NoCompression:
                     zlibCompressionLevel = ZLibNative.CompressionLevel.NoCompression;
-                    windowBits = -15;
+                    windowBits = ZLibNative.Deflate_DefaultWindowBits;
                     memLevel = 7;
-                    strategy = ZLibNative.CompressionStrategy.DefaultStrategy;
                     break;
 
                 default: