Optimize for case where no matches are found

- Add additional parameter to replaceString that returns whether a match was found
- Wait to allocate memory until a match is made rather than at the beginning of the search
- Avoid copying source into result if source wasn't changed

rtl/eclrtl/eclrtl.cpp

@@ -6066,7 +6066,13 @@ void rtlAddExceptionTag(StringBuffer & errorText, const char * tag, const char *
 void rtlSubstituteEmbeddedScript(size32_t &__lenResult, char * &__result, size32_t scriptChars, const char *script, size32_t outFieldsChars, const char *outFields, size32_t searchChars, const char *search)
 {
     StringBuffer result;
-    ::replaceString(result, rtlUtf8Size(scriptChars, script), script, rtlUtf8Size(searchChars, search), search, rtlUtf8Size(outFieldsChars, outFields), outFields);
+    bool foundMatch = false;
+    size_t sourceLen = rtlUtf8Size(scriptChars, script);
+    ::replaceString(result, sourceLen, script, rtlUtf8Size(searchChars, search), search, rtlUtf8Size(outFieldsChars, outFields), outFields, foundMatch);
+
+    if (!foundMatch)
+        result.append(sourceLen, script);
+
     __lenResult = result.lengthUtf8();
     __result = result.detach();
 }

system/jlib/jstring.cpp

@@ -935,22 +935,28 @@ StringBuffer & StringBuffer::replace(char oldChar, char newChar)
 }
 
 // Copy source to result, replacing all occurrences of "oldStr" with "newStr"
-StringBuffer &replaceString(StringBuffer & result, size_t lenSource, const char *source, size_t lenOldStr, const char* oldStr, size_t lenNewStr, const char* newStr)
+StringBuffer &replaceString(StringBuffer & result, size_t lenSource, const char *source, size_t lenOldStr, const char* oldStr, size_t lenNewStr, const char* newStr, bool & foundMatch)
 {
     if (lenOldStr && lenSource >= lenOldStr)
     {
-        // Avoid allocating an unnecessarly large buffer and match the source string
-        result.ensureCapacity(lenSource);
-
         size_t offset = 0;
         size_t lastCopied = 0;
         size_t maxOffset = lenSource - lenOldStr + 1;
         char firstChar = oldStr[0];
+        foundMatch = false;
         while (offset < maxOffset)
         {
             if (unlikely(source[offset] == firstChar)
                 && unlikely((lenOldStr == 1) || memcmp(source + offset, oldStr, lenOldStr)==0))
             {
+                // Wait to allocate memory until a match is found
+                if (unlikely(!foundMatch))
+                {
+                    // Avoid allocating an unnecessarly large buffer and match the source string
+                    result.ensureCapacity(lenSource);
+                    foundMatch = true;
+                }
+
                 // If lastCopied matches the offset nothing is appended, but we can avoid a test for offset == lastCopied
                 result.append(offset - lastCopied, source + lastCopied);
                 result.append(lenNewStr, newStr);
@@ -960,11 +966,10 @@ StringBuffer &replaceString(StringBuffer & result, size_t lenSource, const char
             else
                 offset++;
         }
-        // Append the remaining characters
-        result.append(lenSource - lastCopied, source + lastCopied);
+
+        if (foundMatch)
+            result.append(lenSource - lastCopied, source + lastCopied); // Append the remaining characters
     }
-    else
-        result.append(lenSource, source); // Search string does not fit in source or is empty
 
     return result;
 }
@@ -1075,7 +1080,12 @@ StringBuffer & StringBuffer::replaceString(const char* oldStr, const char* newSt
         else
         {
             StringBuffer temp;
-            ::replaceString(temp, curLen, buffer, oldlen, oldStr, newlen, newStr);
+            bool foundMatch = false;
+            ::replaceString(temp, curLen, buffer, oldlen, oldStr, newlen, newStr, foundMatch);
+
+            if (!foundMatch)
+                return *this;
+
             swapWith(temp);
         }
     }

system/jlib/jstring.hpp

@@ -407,7 +407,7 @@ extern jlib_decl void decodeXML(ISimpleReadStream &in, StringBuffer &out, unsign
 extern jlib_decl int utf8CharLen(unsigned char ch);
 extern jlib_decl int utf8CharLen(const unsigned char *ch, unsigned maxsize = (unsigned)-1);
 
-extern jlib_decl StringBuffer &replaceString(StringBuffer & result, size_t lenSource, const char *source, size_t lenOldStr, const char* oldStr, size_t lenNewStr, const char* newStr);
+extern jlib_decl StringBuffer &replaceString(StringBuffer & result, size_t lenSource, const char *source, size_t lenOldStr, const char* oldStr, size_t lenNewStr, const char* newStr, bool & foundMatch);
 
 interface IVariableSubstitutionHelper
 {