GStreamer: metadata - reduce complexity for metadata lookup

Instead of doing a linear search, we can do a binary search in a
constexpr array. Reducing O(N) to O(log(N)).

Pick-to: 6.5
Change-Id: I5bdc42bfc73dc9993e80c7352d64e54bbffe9a28
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
Reviewed-by:  Alexey Edelev <alexey.edelev@qt.io>
(cherry picked from commit f0dca46cdcc406ade7b06f765a64c8522bd9c84b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

6 files changed, 185 insertions, 53 deletions

diff --git a/src/plugins/multimedia/gstreamer/CMakeLists.txt b/src/plugins/multimedia/gstreamer/CMakeLists.txt
index 91fca82a3..80fc1fce0 100644
--- a/src/plugins/multimedia/gstreamer/CMakeLists.txt
+++ b/src/plugins/multimedia/gstreamer/CMakeLists.txt
@@ -52,13 +52,14 @@ qt_internal_add_module(QGstreamerMediaPluginPrivate
 )
 
 qt_internal_extend_target(QGstreamerMediaPluginPrivate CONDITION QT_FEATURE_gstreamer_photography
-    LIBRARIES
+    PUBLIC_LIBRARIES
         GStreamer::Photography
 )
 
 qt_internal_extend_target(QGstreamerMediaPluginPrivate CONDITION QT_FEATURE_gstreamer_gl
-    LIBRARIES
+    PUBLIC_LIBRARIES
         GStreamer::Gl
+    LIBRARIES
         EGL::EGL
 )
 
diff --git a/src/plugins/multimedia/gstreamer/common/qgstreamermetadata.cpp b/src/plugins/multimedia/gstreamer/common/qgstreamermetadata.cpp
index 953acb56a..b02e3e40f 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstreamermetadata.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgstreamermetadata.cpp
@@ -15,77 +15,135 @@
 
 QT_BEGIN_NAMESPACE
 
-struct {
-    const char *tag;
-    QMediaMetaData::Key key;
-} gstTagToMetaDataKey[] = {
-    { GST_TAG_TITLE, QMediaMetaData::Title },
-    { GST_TAG_COMMENT, QMediaMetaData::Comment },
-    { GST_TAG_DESCRIPTION, QMediaMetaData::Description },
-    { GST_TAG_GENRE, QMediaMetaData::Genre },
-    { GST_TAG_DATE_TIME, QMediaMetaData::Date },
-    { GST_TAG_DATE, QMediaMetaData::Date },
+namespace {
 
-    { GST_TAG_LANGUAGE_CODE, QMediaMetaData::Language },
+namespace MetadataLookupImpl {
 
-    { GST_TAG_ORGANIZATION, QMediaMetaData::Publisher },
-    { GST_TAG_COPYRIGHT, QMediaMetaData::Copyright },
+#ifdef __cpp_lib_constexpr_algorithms
+#  define constexpr_lookup constexpr
+#else
+#  define constexpr_lookup /*constexpr*/
+#endif
 
-    // Media
-    { GST_TAG_DURATION, QMediaMetaData::Duration },
+struct MetadataKeyValuePair
+{
+    const char *tag;
+    QMediaMetaData::Key key;
+};
 
-    // Audio
-    { GST_TAG_BITRATE, QMediaMetaData::AudioBitRate },
-    { GST_TAG_AUDIO_CODEC, QMediaMetaData::AudioCodec },
+constexpr const char *toTag(const char *t)
+{
+    return t;
+}
+constexpr const char *toTag(const MetadataKeyValuePair &kv)
+{
+    return kv.tag;
+}
 
-    // Music
-    { GST_TAG_ALBUM, QMediaMetaData::AlbumTitle },
-    { GST_TAG_ALBUM_ARTIST, QMediaMetaData::AlbumArtist },
-    { GST_TAG_ARTIST, QMediaMetaData::ContributingArtist },
-    { GST_TAG_TRACK_NUMBER, QMediaMetaData::TrackNumber },
+constexpr QMediaMetaData::Key toKey(QMediaMetaData::Key k)
+{
+    return k;
+}
+constexpr QMediaMetaData::Key toKey(const MetadataKeyValuePair &kv)
+{
+    return kv.key;
+}
 
-    { GST_TAG_PREVIEW_IMAGE, QMediaMetaData::ThumbnailImage },
-    { GST_TAG_IMAGE, QMediaMetaData::CoverArtImage },
+constexpr auto compareByKey = [](const auto &lhs, const auto &rhs) {
+    return toKey(lhs) < toKey(rhs);
+};
 
-    // Image/Video
-    { "resolution", QMediaMetaData::Resolution },
-    { GST_TAG_IMAGE_ORIENTATION, QMediaMetaData::Orientation },
+constexpr auto compareByTag = [](const auto &lhs, const auto &rhs) {
+    return std::strcmp(toTag(lhs), toTag(rhs)) < 0;
+};
 
-    // Video
-    { GST_TAG_VIDEO_CODEC, QMediaMetaData::VideoCodec },
+constexpr_lookup auto makeLookupTable()
+{
+    std::array<MetadataKeyValuePair, 22> lookupTable{ {
+            { GST_TAG_TITLE, QMediaMetaData::Title },
+            { GST_TAG_COMMENT, QMediaMetaData::Comment },
+            { GST_TAG_DESCRIPTION, QMediaMetaData::Description },
+            { GST_TAG_GENRE, QMediaMetaData::Genre },
+            { GST_TAG_DATE_TIME, QMediaMetaData::Date },
+            { GST_TAG_DATE, QMediaMetaData::Date },
+
+            { GST_TAG_LANGUAGE_CODE, QMediaMetaData::Language },
+
+            { GST_TAG_ORGANIZATION, QMediaMetaData::Publisher },
+            { GST_TAG_COPYRIGHT, QMediaMetaData::Copyright },
+
+            // Media
+            { GST_TAG_DURATION, QMediaMetaData::Duration },
+
+            // Audio
+            { GST_TAG_BITRATE, QMediaMetaData::AudioBitRate },
+            { GST_TAG_AUDIO_CODEC, QMediaMetaData::AudioCodec },
+
+            // Music
+            { GST_TAG_ALBUM, QMediaMetaData::AlbumTitle },
+            { GST_TAG_ALBUM_ARTIST, QMediaMetaData::AlbumArtist },
+            { GST_TAG_ARTIST, QMediaMetaData::ContributingArtist },
+            { GST_TAG_TRACK_NUMBER, QMediaMetaData::TrackNumber },
+
+            { GST_TAG_PREVIEW_IMAGE, QMediaMetaData::ThumbnailImage },
+            { GST_TAG_IMAGE, QMediaMetaData::CoverArtImage },
+
+            // Image/Video
+            { "resolution", QMediaMetaData::Resolution },
+            { GST_TAG_IMAGE_ORIENTATION, QMediaMetaData::Orientation },
+
+            // Video
+            { GST_TAG_VIDEO_CODEC, QMediaMetaData::VideoCodec },
+
+            // Movie
+            { GST_TAG_PERFORMER, QMediaMetaData::LeadPerformer },
+    } };
+
+    std::sort(lookupTable.begin(), lookupTable.end(),
+              [](const MetadataKeyValuePair &lhs, const MetadataKeyValuePair &rhs) {
+                  return std::string_view(lhs.tag) < std::string_view(rhs.tag);
+              });
+    return lookupTable;
+}
 
-    // Movie
-    { GST_TAG_PERFORMER, QMediaMetaData::LeadPerformer },
+constexpr_lookup auto gstTagToMetaDataKey = makeLookupTable();
+constexpr_lookup auto metaDataKeyToGstTag = [] {
+    auto array = gstTagToMetaDataKey;
+    std::sort(array.begin(), array.end(), compareByKey);
+    return array;
+}();
 
-    { nullptr, QMediaMetaData::Title }
-};
+} // namespace MetadataLookupImpl
 
-static QMediaMetaData::Key tagToKey(const char *tag)
+QMediaMetaData::Key tagToKey(const char *tag)
 {
-    auto *map = gstTagToMetaDataKey;
-    while (map->tag) {
-        if (!strcmp(map->tag, tag))
-            return map->key;
-        ++map;
-    }
+    if (tag == nullptr)
+        return QMediaMetaData::Key(-1);
+
+    using namespace MetadataLookupImpl;
+    auto foundIterator = std::lower_bound(gstTagToMetaDataKey.begin(), gstTagToMetaDataKey.end(),
+                                          tag, compareByTag);
+    if (std::strcmp(foundIterator->tag, tag) == 0)
+        return foundIterator->key;
+
     return QMediaMetaData::Key(-1);
 }
 
-static const char *keyToTag(QMediaMetaData::Key key)
+const char *keyToTag(QMediaMetaData::Key key)
 {
-    auto *map = gstTagToMetaDataKey;
-    while (map->tag) {
-        if (map->key == key)
-            return map->tag;
-        ++map;
-    }
+    using namespace MetadataLookupImpl;
+    auto foundIterator = std::lower_bound(metaDataKeyToGstTag.begin(), metaDataKeyToGstTag.end(),
+                                          key, compareByKey);
+    if (foundIterator->key == key)
+        return foundIterator->tag;
+
     return nullptr;
 }
 
+#undef constexpr_lookup
+
 //internal
-static void addTagToMap(const GstTagList *list,
-                        const gchar *tag,
-                        gpointer user_data)
+void addTagToMap(const GstTagList *list, const gchar *tag, gpointer user_data)
 {
     QMediaMetaData::Key key = tagToKey(tag);
     if (key == QMediaMetaData::Key(-1))
@@ -187,6 +245,7 @@ static void addTagToMap(const GstTagList *list,
     g_value_unset(&val);
 }
 
+} // namespace
 
 QGstreamerMetaData QGstreamerMetaData::fromGstTagList(const GstTagList *tags)
 {
diff --git a/tests/auto/unit/multimedia/CMakeLists.txt b/tests/auto/unit/multimedia/CMakeLists.txt
index c6663a800..345c1679c 100644
--- a/tests/auto/unit/multimedia/CMakeLists.txt
+++ b/tests/auto/unit/multimedia/CMakeLists.txt
@@ -30,3 +30,7 @@ add_subdirectory(qmediadevices)
 add_subdirectory(qerrorinfo)
 add_subdirectory(qvideobuffers)
 add_subdirectory(qwavedecoder)
+
+if (QT_FEATURE_gstreamer)
+    add_subdirectory(gstreamer_backend)
+endif()
diff --git a/tests/auto/unit/multimedia/gstreamer_backend/CMakeLists.txt b/tests/auto/unit/multimedia/gstreamer_backend/CMakeLists.txt
new file mode 100644
index 000000000..6d52d09e1
--- /dev/null
+++ b/tests/auto/unit/multimedia/gstreamer_backend/CMakeLists.txt
@@ -0,0 +1,15 @@
+# Copyright (C) 2024 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+#####################################################################
+## tst_gstreamer_backend Test:
+#####################################################################
+
+qt_internal_add_test(tst_gstreamer_backend
+    SOURCES
+        tst_gstreamer_backend.cpp
+        tst_gstreamer_backend.h
+    LIBRARIES
+        Qt::MultimediaPrivate
+        Qt::QGstreamerMediaPluginPrivate
+)
diff --git a/tests/auto/unit/multimedia/gstreamer_backend/tst_gstreamer_backend.cpp b/tests/auto/unit/multimedia/gstreamer_backend/tst_gstreamer_backend.cpp
new file mode 100644
index 000000000..3b4577ca2
--- /dev/null
+++ b/tests/auto/unit/multimedia/gstreamer_backend/tst_gstreamer_backend.cpp
@@ -0,0 +1,29 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#include "tst_gstreamer_backend.h"
+
+#include <QtTest/QtTest>
+#include <QtQGstreamerMediaPlugin/private/qgstreamermetadata_p.h>
+#include <QtQGstreamerMediaPlugin/private/qgst_handle_types_p.h>
+
+QT_USE_NAMESPACE
+
+using namespace Qt::Literals;
+
+void tst_GStreamer::metadata_fromGstTagList()
+{
+    QGstTagListHandle tagList{
+        gst_tag_list_new_from_string(R"(taglist, title="My Video", comment="yada")"),
+        QGstTagListHandle::NeedsRef,
+    };
+
+    QGstreamerMetaData parsed = QGstreamerMetaData::fromGstTagList(tagList.get());
+
+    QCOMPARE(parsed.stringValue(QMediaMetaData::Title), u"My Video"_s);
+    QCOMPARE(parsed.stringValue(QMediaMetaData::Comment), u"yada"_s);
+}
+
+QTEST_GUILESS_MAIN(tst_GStreamer)
+
+#include "moc_tst_gstreamer_backend.cpp"
diff --git a/tests/auto/unit/multimedia/gstreamer_backend/tst_gstreamer_backend.h b/tests/auto/unit/multimedia/gstreamer_backend/tst_gstreamer_backend.h
new file mode 100644
index 000000000..5bac3a599
--- /dev/null
+++ b/tests/auto/unit/multimedia/gstreamer_backend/tst_gstreamer_backend.h
@@ -0,0 +1,24 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#ifndef TST_GSTREAMER_BACKEND_H
+#define TST_GSTREAMER_BACKEND_H
+
+#include <QtTest/QtTest>
+
+#include <QtQGstreamerMediaPlugin/private/qgstreamerintegration_p.h>
+
+QT_USE_NAMESPACE
+
+class tst_GStreamer : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void metadata_fromGstTagList();
+
+private:
+    QGstreamerIntegration integration;
+};
+
+#endif // TST_GSTREAMER_BACKEND_H