QStringAlgorithms/private: prefer to trim whitespace from the end

When calculating what to trim in trimmed_helper_positions(), first
trim the end, then the front.

This way, a string that consists of just whitespace will remain
anchored at its front, and we do not run into the memmove case in
trimmed_helper_inplace, which, even though there's zero elements to
move, still calls a potentially-out-of-line function (memmove()).

Change-Id: I7024ffa1f7ae2effb9c5166ec8f30a42b8d51079
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/src/corelib/tools/qstringalgorithms_p.h b/src/corelib/tools/qstringalgorithms_p.h
index c5470bc7ad..4bcf697f78 100644
--- a/src/corelib/tools/qstringalgorithms_p.h
+++ b/src/corelib/tools/qstringalgorithms_p.h
@@ -89,14 +89,12 @@ template <typename StringType> struct QStringAlgorithms
 
     static inline void trimmed_helper_positions(const Char *&begin, const Char *&end)
     {
+        // skip white space from end
+        while (begin < end && isSpace(end[-1]))
+            --end;
         // skip white space from start
         while (begin < end && isSpace(*begin))
             begin++;
-        // skip white space from end
-        if (begin < end) {
-            while (begin < end && isSpace(end[-1]))
-                end--;
-        }
     }
 
     static inline StringType trimmed_helper(StringType &str)