optimize Replace() for the common case of replacing one character with another one (#9802)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@54860 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -93,6 +93,7 @@ Major new features in 2.8 release
 
 All:
 
+- Optimize wxString::Replace() for single character arguments.
 - Updated Hindi translation (Priyank Bolia).
 
 All (GUI):

src/common/string.cpp

@@ -1492,8 +1492,8 @@ wxString wxString::AfterFirst(wxChar ch) const
 }
 
 // replace first (or all) occurences of some substring with another one
-size_t wxString::Replace(const wxChar *szOld,
-                  const wxChar *szNew, bool bReplaceAll)
+size_t
+wxString::Replace(const wxChar *szOld, const wxChar *szNew, bool bReplaceAll)
 {
     // if we tried to replace an empty string we'd enter an infinite loop below
     wxCHECK_MSG( szOld && *szOld && szNew, 0,
@@ -1501,33 +1501,48 @@ size_t wxString::Replace(const wxChar *szOld,
 
     size_t uiCount = 0;   // count of replacements made
 
-    size_t uiOldLen = wxStrlen(szOld);
-    size_t uiNewLen = wxStrlen(szNew);
-
-    size_t dwPos = 0;
-
-    while ( this->c_str()[dwPos] != wxT('\0') )
+    // optimize the special common case of replacing one character with another
+    // one
+    if ( szOld[1] == '\0' && szNew[1] == '\0' )
     {
-        //DO NOT USE STRSTR HERE
-        //this string can contain embedded null characters,
-        //so strstr will function incorrectly
-        dwPos = find(szOld, dwPos);
-        if ( dwPos == npos )
-            break;                  // exit the loop
-        else
+        // this loop is the simplified version of the one below
+        for ( size_t pos = 0; ; )
         {
-            //replace this occurance of the old string with the new one
-            replace(dwPos, uiOldLen, szNew, uiNewLen);
+            pos = find(*szOld, pos);
+            if ( pos == npos )
+                break;
 
-            //move up pos past the string that was replaced
-            dwPos += uiNewLen;
+            (*this)[pos++] = *szNew;
 
-            //increase replace count
-            ++uiCount;
+            uiCount++;
+
+            if ( !bReplaceAll )
+                break;
+        }
+    }
+    else // general case
+    {
+        const size_t uiOldLen = wxStrlen(szOld);
+        const size_t uiNewLen = wxStrlen(szNew);
+
+        for ( size_t pos = 0; ; )
+        {
+            pos = find(szOld, pos);
+            if ( pos == npos )
+                break;
+
+            // replace this occurrence of the old string with the new one
+            replace(pos, uiOldLen, szNew, uiNewLen);
+
+            // move past the string that was replaced
+            pos += uiNewLen;
+
+            // increase replace count
+            uiCount++;
 
             // stop now?
             if ( !bReplaceAll )
-                break;                  // exit the loop
+                break;
         }
     }