From eaafda06e223fa611b9799a4c148f478bde60c03 Mon Sep 17 00:00:00 2001
From: Ian Hays <ianha@microsoft.com>
Date: Fri, 15 Jan 2016 11:34:30 -0800
Subject: [PATCH] System.IO.Compression: Make CompressionLevel.Optimal = -1

CompressionLevel 6 is what we used to use and we changed it in #4589 because we didn't see any perf regressions in doing so. With more testing, it has become clear that moving from 6 to 9 severely hurt perf in some scenarios so it's being reverted to -1 which maps to 6.
---
 src/Native/System.IO.Compression.Native/pal_zlib.cpp        | 2 +-
 src/Native/System.IO.Compression.Native/pal_zlib.h          | 2 +-
 .../src/System/IO/Compression/Deflater.cs                   | 2 +-
 .../src/System/IO/Compression/ZLibNative.cs                 | 6 +++---
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/Native/System.IO.Compression.Native/pal_zlib.cpp b/src/Native/System.IO.Compression.Native/pal_zlib.cpp
index 999b38c2e0dd..d049903311a5 100644
--- a/src/Native/System.IO.Compression.Native/pal_zlib.cpp
+++ b/src/Native/System.IO.Compression.Native/pal_zlib.cpp
@@ -20,7 +20,7 @@ static_assert(PAL_Z_VERSIONERROR == Z_VERSION_ERROR, "");
 
 static_assert(PAL_Z_NOCOMPRESSION == Z_NO_COMPRESSION, "");
 static_assert(PAL_Z_BESTSPEED == Z_BEST_SPEED, "");
-static_assert(PAL_Z_BESTCOMPRESSION == Z_BEST_COMPRESSION, "");
+static_assert(PAL_Z_DEFAULTCOMPRESSION == Z_DEFAULT_COMPRESSION, "");
 
 static_assert(PAL_Z_DEFAULTSTRATEGY == Z_DEFAULT_STRATEGY, "");
 
diff --git a/src/Native/System.IO.Compression.Native/pal_zlib.h b/src/Native/System.IO.Compression.Native/pal_zlib.h
index 9b61824abb8a..3fd48d29c371 100644
--- a/src/Native/System.IO.Compression.Native/pal_zlib.h
+++ b/src/Native/System.IO.Compression.Native/pal_zlib.h
@@ -50,7 +50,7 @@ enum PAL_CompressionLevel : int32_t
 {
     PAL_Z_NOCOMPRESSION = 0,
     PAL_Z_BESTSPEED = 1,
-    PAL_Z_BESTCOMPRESSION = 9,
+    PAL_Z_DEFAULTCOMPRESSION = -1,
 };
 
 /*
diff --git a/src/System.IO.Compression/src/System/IO/Compression/Deflater.cs b/src/System.IO.Compression/src/System/IO/Compression/Deflater.cs
index 109965e7bd44..49dee00bd024 100644
--- a/src/System.IO.Compression/src/System/IO/Compression/Deflater.cs
+++ b/src/System.IO.Compression/src/System/IO/Compression/Deflater.cs
@@ -42,7 +42,7 @@ internal Deflater(CompressionLevel compressionLevel, int windowBits)
                 // See the note in ZLibNative.CompressionLevel for the recommended combinations.
 
                 case CompressionLevel.Optimal:
-                    zlibCompressionLevel = ZLibNative.CompressionLevel.BestCompression;
+                    zlibCompressionLevel = ZLibNative.CompressionLevel.DefaultCompression;
                     memLevel = ZLibNative.Deflate_DefaultMemLevel;
                     break;
 
diff --git a/src/System.IO.Compression/src/System/IO/Compression/ZLibNative.cs b/src/System.IO.Compression/src/System/IO/Compression/ZLibNative.cs
index 125bf4b83a60..6982a014a150 100644
--- a/src/System.IO.Compression/src/System/IO/Compression/ZLibNative.cs
+++ b/src/System.IO.Compression/src/System/IO/Compression/ZLibNative.cs
@@ -48,10 +48,10 @@ public enum ErrorCode : int
         /// 
         /// <p><strong>How to choose a compression level:</strong></p>
         /// 
-        /// <p>The names <code>NoCompression</code>, <code>BestSpeed</code>, <code>BestCompression</code> are taken over from the corresponding
+        /// <p>The names <code>NoCompression</code>, <code>BestSpeed</code>, <code>DefaultCompression</code> are taken over from the corresponding
         /// ZLib definitions, which map to our public NoCompression, Fastest, and Optimal respectively.
         /// <p><em>Optimal Compression:</em></p>
-        /// <p><code>ZLibNative.CompressionLevel compressionLevel = ZLibNative.CompressionLevel.BestCompression;</code> <br />
+        /// <p><code>ZLibNative.CompressionLevel compressionLevel = ZLibNative.CompressionLevel.DefaultCompression;</code> <br />
         ///    <code>Int32 windowBits = 15;  // or -15 if no headers required</code> <br />
         ///    <code>Int32 memLevel = 8;</code> <br />
         ///    <code>ZLibNative.CompressionStrategy strategy = ZLibNative.CompressionStrategy.DefaultStrategy;</code> </p>
@@ -72,7 +72,7 @@ public enum CompressionLevel : int
         {
             NoCompression = 0,
             BestSpeed = 1,
-            BestCompression = 9,    // Refer to "How to choose a compression level" above.
+            DefaultCompression = -1
         }
 
         /// <summary>