Bug 665858 - Part 1: Optimize the conversion of native and cross platform text offsets; r=roc,masayuki

content/events/src/nsContentEventHandler.cpp

@@ -188,15 +188,6 @@ static void ConvertToNativeNewlines(nsAFlatString& aString)
 #endif
 }
 
-static void ConvertToXPNewlines(nsAFlatString& aString)
-{
-#if defined(XP_MACOSX)
-  aString.ReplaceSubstring(NS_LITERAL_STRING("\r"), NS_LITERAL_STRING("\n"));
-#elif defined(XP_WIN)
-  aString.ReplaceSubstring(NS_LITERAL_STRING("\r\n"), NS_LITERAL_STRING("\n"));
-#endif
-}
-
 static void AppendString(nsAString& aString, nsIContent* aContent)
 {
   NS_ASSERTION(aContent->IsNodeOfType(nsINode::eTEXT),
@@ -218,28 +209,76 @@ static void AppendSubString(nsAString& aString, nsIContent* aContent,
   text->AppendTo(aString, PRInt32(aXPOffset), PRInt32(aXPLength));
 }
 
+#if defined(XP_WIN)
+static PRUint32 CountNewlinesIn(nsIContent* aContent, PRUint32 aMaxOffset)
+{
+  NS_ASSERTION(aContent->IsNodeOfType(nsINode::eTEXT),
+               "aContent is not a text node!");
+  const nsTextFragment* text = aContent->GetText();
+  if (!text)
+    return 0;
+  if (aMaxOffset == PR_UINT32_MAX) {
+    // search the entire string
+    aMaxOffset = text->GetLength();
+  }
+  PRUint32 newlines = 0;
+  for (PRUint32 i = 0; i < aMaxOffset; ++i) {
+    if (text->CharAt(i) == '\n') {
+      ++newlines;
+    }
+  }
+  return newlines;
+}
+#endif
+
 static PRUint32 GetNativeTextLength(nsIContent* aContent)
 {
-  nsAutoString str;
-  if (aContent->IsNodeOfType(nsINode::eTEXT))
-    AppendString(str, aContent);
-  else if (IsContentBR(aContent))
-    str.Assign(PRUnichar('\n'));
-  ConvertToNativeNewlines(str);
-  return str.Length();
+  if (aContent->IsNodeOfType(nsINode::eTEXT)) {
+    PRUint32 textLengthDifference =
+#if defined(XP_MACOSX)
+      // On Mac, the length of a native newline ("\r") is equal to the length of
+      // the XP newline ("\n"), so the native length is the same as the XP length.
+      0;
+#elif defined(XP_WIN)
+      // On Windows, the length of a native newline ("\r\n") is twice the length of
+      // the XP newline ("\n"), so XP length is equal to the length of the native
+      // offset plus the number of newlines encountered in the string.
+      CountNewlinesIn(aContent, PR_UINT32_MAX);
+#else
+      // On other platforms, the native and XP newlines are the same.
+      0;
+#endif
+
+    const nsTextFragment* text = aContent->GetText();
+    if (!text)
+      return 0;
+    return text->GetLength() + textLengthDifference;
+  } else if (IsContentBR(aContent)) {
+#if defined(XP_WIN)
+    // Length of \r\n
+    return 2;
+#else
+    return 1;
+#endif
+  }
+  return 0;
 }
 
 static PRUint32 ConvertToXPOffset(nsIContent* aContent, PRUint32 aNativeOffset)
 {
-
-  nsAutoString str;
-  AppendString(str, aContent);
-  ConvertToNativeNewlines(str);
-  NS_ASSERTION(aNativeOffset <= str.Length(),
-               "aOffsetForNativeLF is too large!");
-  str.Truncate(aNativeOffset);
-  ConvertToXPNewlines(str);
-  return str.Length();
+#if defined(XP_MACOSX)
+  // On Mac, the length of a native newline ("\r") is equal to the length of
+  // the XP newline ("\n"), so the native offset is the same as the XP offset.
+  return aNativeOffset;
+#elif defined(XP_WIN)
+  // On Windows, the length of a native newline ("\r\n") is twice the length of
+  // the XP newline ("\n"), so XP offset is equal to the length of the native
+  // offset minus the number of newlines encountered in the string.
+  return aNativeOffset - CountNewlinesIn(aContent, aNativeOffset);
+#else
+  // On other platforms, the native and XP newlines are the same.
+  return aNativeOffset;
+#endif
 }
 
 static nsresult GenerateFlatTextContent(nsIRange* aRange,