From 57b4b45cbdee00f7e38e5eb57d2bcf42201dc74e Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Wed, 31 Oct 2018 19:13:29 -0700
Subject: [PATCH] RCC: introduce compression algorithm "best"

This compression algorithm is permitted in the XML sources, which
instructs RCC to apply the best compression algorithm it has available.
If we have Zstandard available, that's its level 19 (levels 20 and up
are experimental). If not, we apply zlib compression level 9.

And apply this technique for the XDG MIME database that is built-in to
QtCore.
             Payload size  Compr. time
 Previously        313916    17.9ms
 Zlib -9           310899    53.6ms
 Zstd -14          253364    63.3ms (plus 4.0 ms on L1 heuristic check)
 Zstd -19          230647   642.5ms

Change-Id: I343f2beed55440a7ac0bfffd1562de44dbaf09cd
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
---
 src/corelib/mimetypes/mimetypes.qrc |  2 +-
 src/tools/rcc/rcc.cpp               | 11 +++++++++++
 src/tools/rcc/rcc.h                 |  1 +
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/corelib/mimetypes/mimetypes.qrc b/src/corelib/mimetypes/mimetypes.qrc
index 19bc1d3e2a9..4720bd302ac 100644
--- a/src/corelib/mimetypes/mimetypes.qrc
+++ b/src/corelib/mimetypes/mimetypes.qrc
@@ -1,5 +1,5 @@
 <RCC>
     <qresource prefix="/qt-project.org/qmime/packages">
-        <file alias="freedesktop.org.xml">mime/packages/freedesktop.org.xml</file>
+        <file alias="freedesktop.org.xml" compression-algorithm="best">mime/packages/freedesktop.org.xml</file>
     </qresource>
 </RCC>
diff --git a/src/tools/rcc/rcc.cpp b/src/tools/rcc/rcc.cpp
index dfa62cea1be..5cbc7719942 100644
--- a/src/tools/rcc/rcc.cpp
+++ b/src/tools/rcc/rcc.cpp
@@ -258,6 +258,10 @@ qint64 RCCFileInfo::writeDataBlob(RCCResourceLibrary &lib, qint64 offset,
     // Check if compression is useful for this file
     if (data.size() != 0) {
 #if QT_CONFIG(zstd)
+        if (m_compressAlgo == RCCResourceLibrary::CompressionAlgorithm::Best) {
+            m_compressAlgo = RCCResourceLibrary::CompressionAlgorithm::Zstd;
+            m_compressLevel = 19;   // not ZSTD_maxCLevel(), as 20+ are experimental
+        }
         if (m_compressAlgo == RCCResourceLibrary::CompressionAlgorithm::Zstd) {
             if (lib.m_zstdCCtx == nullptr)
                 lib.m_zstdCCtx = ZSTD_createCCtx();
@@ -301,6 +305,10 @@ qint64 RCCFileInfo::writeDataBlob(RCCResourceLibrary &lib, qint64 offset,
         }
 #endif
 #ifndef QT_NO_COMPRESS
+        if (m_compressAlgo == RCCResourceLibrary::CompressionAlgorithm::Best) {
+            m_compressAlgo = RCCResourceLibrary::CompressionAlgorithm::Zlib;
+            m_compressLevel = 9;
+        }
         if (m_compressAlgo == RCCResourceLibrary::CompressionAlgorithm::Zlib) {
             QByteArray compressed =
                     qCompress(reinterpret_cast<uchar *>(data.data()), data.size(), m_compressLevel);
@@ -824,6 +832,8 @@ RCCResourceLibrary::ResourceDataFileMap RCCResourceLibrary::resourceDataFileMap(
 
 RCCResourceLibrary::CompressionAlgorithm RCCResourceLibrary::parseCompressionAlgorithm(QStringView value, QString *errorMsg)
 {
+    if (value == QLatin1String("best"))
+        return CompressionAlgorithm::Best;
     if (value == QLatin1String("zlib")) {
 #ifdef QT_NO_COMPRESS
         *errorMsg = QLatin1String("zlib support not compiled in");
@@ -850,6 +860,7 @@ int RCCResourceLibrary::parseCompressionLevel(CompressionAlgorithm algo, const Q
     if (ok) {
         switch (algo) {
         case CompressionAlgorithm::None:
+        case CompressionAlgorithm::Best:
             return 0;
         case CompressionAlgorithm::Zlib:
             if (c >= 1 && c <= 9)
diff --git a/src/tools/rcc/rcc.h b/src/tools/rcc/rcc.h
index fe8ed21fb3c..7603a41cdea 100644
--- a/src/tools/rcc/rcc.h
+++ b/src/tools/rcc/rcc.h
@@ -84,6 +84,7 @@ public:
         Zlib,
         Zstd,
 
+        Best = 99,
         None = -1
     };