rewrite FilterInValue() using iterators, this results iin 12x performance improvement in UTF-8 build

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@47577 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/fileconf.cpp

@@ -1961,13 +1961,28 @@ int CompareGroups(wxFileConfigGroup *p1, wxFileConfigGroup *p2)
 static wxString FilterInValue(const wxString& str)
 {
     wxString strResult;
-  strResult.Alloc(str.Len());
+    if ( str.empty() )
+        return strResult;
 
-  bool bQuoted = !str.empty() && str[0] == '"';
+    strResult.reserve(str.length());
 
-  for ( size_t n = bQuoted ? 1 : 0; n < str.Len(); n++ ) {
-    if ( str[n] == wxT('\\') ) {
-      switch ( str[++n].GetValue() ) {
+    wxString::const_iterator i = str.begin();
+    const bool bQuoted = *i == '"';
+    if ( bQuoted )
+        ++i;
+
+    for ( const wxString::const_iterator end = str.end(); i != end; ++i )
+    {
+        if ( *i == wxT('\\') )
+        {
+            if ( ++i == end )
+            {
+                wxLogWarning(_("trailing backslash ignored in '%s'"), str.c_str());
+                break;
+            }
+
+            switch ( (*i).GetValue() )
+            {
                 case wxT('n'):
                     strResult += wxT('\n');
                     break;
@@ -1989,12 +2004,16 @@ static wxString FilterInValue(const wxString& str)
                     break;
             }
         }
-    else {
-      if ( str[n] != wxT('"') || !bQuoted )
-        strResult += str[n];
-      else if ( n != str.Len() - 1 ) {
+        else // not a backslash
+        {
+            if ( *i != wxT('"') || !bQuoted )
+            {
+                strResult += *i;
+            }
+            else if ( i != end - 1 )
+            {
                 wxLogWarning(_("unexpected \" at position %d in '%s'."),
-                     n, str.c_str());
+                             i - str.begin(), str.c_str());
             }
             //else: it's the last quote of a quoted string, ok
         }