Look for entries with common group prefix in entryMap's subrange

entryMap is ordered by the group name first. So there is no need to
iterate over the entire map to process entries whose group names start
with some prefix. Find the group name prefix's lower bound and iterate
over the proper subrange instead. This should be much faster, especially
if the subrange's size is much less than the entryMap's size.

Adjust isGroupOrSubGroupMatch() helper function to assert the extracted
startsWith() condition instead of rechecking it. Pass
KEntryMapConstIterator in place of the group name to this function in
order to simplify its callers' code. Reuse this helper function in
KConfigPrivate::copyGroup().

1 files changed, 30 insertions, 0 deletions

diff --git a/src/core/kconfigdata_p.h b/src/core/kconfigdata_p.h
index 5e5246f3..beb18f45 100644
--- a/src/core/kconfigdata_p.h
+++ b/src/core/kconfigdata_p.h
@@ -155,6 +155,17 @@ inline bool operator<(const KEntryKey &k1, const KEntryKey &k2)
     return (!k1.bDefault && k2.bDefault);
 }
 
+/**
+ * Returns the minimum key that has @a mGroup == @p group.
+ *
+ * @note The returned "minimum key" is consistent with KEntryKey's operator<().
+ *       The return value of this function can be passed to KEntryMap::lowerBound().
+ */
+inline KEntryKey minimumGroupKey(const QByteArray &group)
+{
+    return KEntryKey(group, QByteArray{}, true, false);
+}
+
 QDebug operator<<(QDebug dbg, const KEntryKey &key);
 QDebug operator<<(QDebug dbg, const KEntry &entry);
 
@@ -230,6 +241,25 @@ public:
     }
 
     bool revertEntry(const QByteArray &group, const QByteArray &key, EntryOptions options, SearchFlags flags = SearchFlags());
+
+    template<typename ConstIteratorUser>
+    void forEachEntryWhoseGroupStartsWith(const QByteArray &groupPrefix, ConstIteratorUser callback) const
+    {
+        for (auto it = lowerBound(minimumGroupKey(groupPrefix)), end = cend(); it != end && it.key().mGroup.startsWith(groupPrefix); ++it) {
+            callback(it);
+        }
+    }
+
+    template<typename ConstIteratorPredicate>
+    bool anyEntryWhoseGroupStartsWith(const QByteArray &groupPrefix, ConstIteratorPredicate predicate) const
+    {
+        for (auto it = lowerBound(minimumGroupKey(groupPrefix)), end = cend(); it != end && it.key().mGroup.startsWith(groupPrefix); ++it) {
+            if (predicate(it)) {
+                return true;
+            }
+        }
+        return false;
+    }
 };
 Q_DECLARE_OPERATORS_FOR_FLAGS(KEntryMap::SearchFlags)
 Q_DECLARE_OPERATORS_FOR_FLAGS(KEntryMap::EntryOptions)