Optimize getNamespaceId (xmlreader)

Adding a map to cache values allows me
20s -> 13s to start LO

Change-Id: If343225def253e29696b96f223cdcb54d0d8525d
Reviewed-on: https://gerrit.libreoffice.org/80290
Tested-by: Jenkins
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

include/xmlreader/xmlreader.hxx

@@ -22,6 +22,7 @@
 
 #include <sal/config.h>
 
+#include <unordered_map>
 #include <stack>
 #include <vector>
 
@@ -172,6 +173,7 @@ private:
     void * fileAddress_;
     NamespaceIris namespaceIris_;
     NamespaceList namespaces_;
+    mutable std::unordered_map<OUString, int> cacheNSIds_;
     ElementStack elements_;
     char const * pos_;
     char const * end_;

xmlreader/source/xmlreader.cxx

@@ -182,11 +182,21 @@ Span XmlReader::getAttributeValue(bool fullyNormalize) {
 }
 
 int XmlReader::getNamespaceId(Span const & prefix) const {
+    OUString spanString = prefix.convertFromUtf8();
+
+    if (auto it = cacheNSIds_.find(spanString); it != cacheNSIds_.end())
+    {
+        return it->second;
+    }
+
     auto i = std::find_if(namespaces_.crbegin(), namespaces_.crend(),
         [&prefix](const NamespaceData& rNamespaceData) { return prefix.equals(rNamespaceData.prefix); });
 
     if (i != namespaces_.rend())
+    {
+        cacheNSIds_[spanString]= i->nsId;
         return i->nsId;
+    }
 
     return NAMESPACE_UNKNOWN;
 }