Performance improvement for transliteration

Tracing CPU usage identified the cost of ICU transliteration: using a static dictionnary to improve performance

BaseToolkit.cpp

@@ -7,6 +7,7 @@
 #include <iomanip>
 #include <algorithm>
 #include <climits>
+#include <map>
 
 #include <locale>
 #include <unicode/ustream.h>
@@ -52,6 +53,13 @@ std::string BaseToolkit::uniqueName(const std::string &basename, std::list<std::
 
 std::string BaseToolkit::transliterate(const std::string &input)
 {
+    // because icu::Transliterator is slow, we keep a dictionnary of already
+    // transliterated texts to be faster during repeated calls (update of user interface)
+    static std::map<std::string, std::string> dictionnary_;
+    std::map<std::string, std::string>::const_iterator existingentry = dictionnary_.find(input);
+
+    if (existingentry == dictionnary_.cend()) {
+
         auto ucs = icu::UnicodeString::fromUTF8(input);
 
         UErrorCode status = U_ZERO_ERROR;
@@ -68,7 +76,12 @@ std::string BaseToolkit::transliterate(const std::string &input)
         std::ostringstream output;
         output << ucs;
 
-    return output.str();
+        // remember for future
+        dictionnary_[input] = output.str();
+    }
+
+    // return remembered transliterated text
+    return dictionnary_[input];
 }