Bug 1358275 - Preliminary cleanup: refactor nsTextFragment::UpdateBidiFlag(), moving its logic into nsBidiUtils function HasRTLChars() and making that function more precise in the process. r=dholbert

dom/base/nsTextFragment.cpp

@@ -450,21 +450,8 @@ void
 nsTextFragment::UpdateBidiFlag(const char16_t* aBuffer, uint32_t aLength)
 {
   if (mState.mIs2b && !mState.mIsBidi) {
-    const char16_t* cp = aBuffer;
-    const char16_t* end = cp + aLength;
-    while (cp < end) {
-      char16_t ch1 = *cp++;
-      uint32_t utf32Char = ch1;
-      if (NS_IS_HIGH_SURROGATE(ch1) &&
-          cp < end &&
-          NS_IS_LOW_SURROGATE(*cp)) {
-        char16_t ch2 = *cp++;
-        utf32Char = SURROGATE_TO_UCS4(ch1, ch2);
-      }
-      if (UTF32_CHAR_IS_BIDI(utf32Char) || IsBidiControlRTL(utf32Char)) {
-        mState.mIsBidi = true;
-        break;
-      }
+    if (HasRTLChars(aBuffer, aLength)) {
+      mState.mIsBidi = true;
     }
   }
 }

intl/unicharutil/util/nsBidiUtils.cpp

@@ -82,16 +82,18 @@ nsresult HandleNumbers(char16_t* aBuffer, uint32_t aSize, uint32_t aNumFlag)
   return NS_OK;
 }
 
-bool HasRTLChars(const nsAString& aString)
+bool HasRTLChars(const char16_t* aText, uint32_t aLength)
 {
-// This is used to determine whether to enable bidi if a string has 
-// right-to-left characters. To simplify things, anything that could be a
-// surrogate or RTL presentation form is covered just by testing >= 0xD800).
-// It's fine to enable bidi in rare cases where it actually isn't needed.
-  int32_t length = aString.Length();
-  for (int32_t i = 0; i < length; i++) {
-    char16_t ch = aString.CharAt(i);
-    if (ch >= 0xD800 || IS_IN_BMP_RTL_BLOCK(ch)) {
+  // This is used to determine whether a string has right-to-left characters
+  // that mean it will require bidi processing.
+  const char16_t* cp = aText;
+  const char16_t* end = cp + aLength;
+  while (cp < end) {
+    uint32_t ch = *cp++;
+    if (NS_IS_HIGH_SURROGATE(ch) && cp < end && NS_IS_LOW_SURROGATE(*cp)) {
+      ch = SURROGATE_TO_UCS4(ch, *cp++);
+    }
+    if (UTF32_CHAR_IS_BIDI(ch) || IsBidiControlRTL(ch)) {
       return true;
     }
   }

intl/unicharutil/util/nsBidiUtils.h

@@ -147,10 +147,17 @@ typedef enum nsCharType nsCharType;
    }
 
   /**
-   * Give an nsString.
+   * Give a 16-bit (UTF-16) text buffer and length
    * @return true if the string contains right-to-left characters
    */
-   bool HasRTLChars(const nsAString& aString);
+   bool HasRTLChars(const char16_t* aText, uint32_t aLength);
+
+  /**
+   * Convenience function to call the above on an nsAString.
+   */
+   inline bool HasRTLChars(const nsAString& aString) {
+     return HasRTLChars(aString.BeginReading(), aString.Length());
+   }
 
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 //  ------------------