From 8a6270322b0767fd7f9956f90538ca55d341fab5 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Wed, 30 Jul 2008 21:41:07 +0000
Subject: [PATCH] optimize Replace() for the common case of replacing one
 character with another one (#9802)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54860 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---
 src/common/string.cpp | 59 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 44 insertions(+), 15 deletions(-)

diff --git a/src/common/string.cpp b/src/common/string.cpp
index c3bc9331cb..362d682fb2 100644
--- a/src/common/string.cpp
+++ b/src/common/string.cpp
@@ -1239,27 +1239,56 @@ size_t wxString::Replace(const wxString& strOld,
 
     size_t uiCount = 0;   // count of replacements made
 
-    const size_t uiOldLen = strOld.m_impl.length();
-    const size_t uiNewLen = strNew.m_impl.length();
+    // optimize the special common case: replacement of one character by
+    // another one (in UTF-8 case we can only do this for ASCII characters)
+    //
+    // benchmarks show that this special version is around 3 times faster
+    // (depending on the proportion of matching characters and UTF-8/wchar_t
+    // build)
+    if ( strOld.m_impl.length() == 1 && strNew.m_impl.length() == 1 )
+    {
+        const wxStringCharType chOld = strOld.m_impl[0],
+                               chNew = strNew.m_impl[0];
+
+        // this loop is the simplified version of the one below
+        for ( size_t pos = 0; ; )
+        {
+            pos = m_impl.find(chOld, pos);
+            if ( pos == npos )
+                break;
 
-    for ( size_t dwPos = 0; dwPos < m_impl.length(); )
+            m_impl[pos++] = chNew;
+
+            uiCount++;
+
+            if ( !bReplaceAll )
+                break;
+        }
+    }
+    else // general case
     {
-        dwPos = m_impl.find(strOld.m_impl, dwPos);
-        if ( dwPos == npos )
-            break;
+        const size_t uiOldLen = strOld.m_impl.length();
+        const size_t uiNewLen = strNew.m_impl.length();
+
+        for ( size_t pos = 0; ; )
+        {
+            pos = m_impl.find(strOld.m_impl, pos);
+            if ( pos == npos )
+                break;
 
-        // replace this occurance of the old string with the new one
-        m_impl.replace(dwPos, uiOldLen, strNew.m_impl);
+            // replace this occurrence of the old string with the new one
+            m_impl.replace(pos, uiOldLen, strNew.m_impl);
 
-        // move up pos past the string that was replaced
-        dwPos += uiNewLen;
+            // move up pos past the string that was replaced
+            pos += uiNewLen;
 
-        // increase replace count
-        ++uiCount;
+            // increase replace count
+            uiCount++;
 
-        // stop after the first one?
-        if ( !bReplaceAll )
-            break;
+            // stop after the first one?
+            if ( !bReplaceAll )
+                break;
+        }
     }
 
     return uiCount;
-- 
2.45.2