Add API call that identifies strings that are guaranteed

only to contain ASCII characters.
Review URL: https://chromiumcodereview.appspot.com/9724022

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11079 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -1020,6 +1020,14 @@ class String : public Primitive {
    */
   V8EXPORT int Utf8Length() const;
 
+  /**
+   * A fast conservative check for non-ASCII characters.  May
+   * return true even for ASCII strings, but if it returns
+   * false you can be sure that all characters are in the range
+   * 0-127.
+   */
+  V8EXPORT bool MayContainNonAscii() const;
+
   /**
    * Write the contents of the string to an external buffer.
    * If no arguments are given, expects the buffer to be large

src/api.cc

@@ -3694,6 +3694,15 @@ int String::Utf8Length() const {
 }
 
 
+bool String::MayContainNonAscii() const {
+  i::Handle<i::String> str = Utils::OpenHandle(this);
+  if (IsDeadCheck(str->GetIsolate(), "v8::String::MayContainNonAscii()")) {
+    return false;
+  }
+  return !str->HasOnlyAsciiChars();
+}
+
+
 int String::WriteUtf8(char* buffer,
                       int capacity,
                       int* nchars_ref,

test/cctest/test-api.cc

@@ -5770,6 +5770,8 @@ static void Utf16Helper(
       Local<v8::String>::Cast(a->Get(i));
     Local<v8::Number> expected_len =
       Local<v8::Number>::Cast(alens->Get(i));
+    CHECK_EQ(expected_len->Value() != string->Length(),
+             string->MayContainNonAscii());
     int length = GetUtf8Length(string);
     CHECK_EQ(static_cast<int>(expected_len->Value()), length);
   }
@@ -11927,6 +11929,9 @@ THREADED_TEST(MorphCompositeStringTest) {
         "var slice = lhs.substring(1, lhs.length - 1);"
         "var slice_on_cons = (lhs + rhs).substring(1, lhs.length *2 - 1);");
 
+    CHECK(!lhs->MayContainNonAscii());
+    CHECK(!rhs->MayContainNonAscii());
+
     MorphAString(*v8::Utils::OpenHandle(*lhs), &ascii_resource, &uc16_resource);
     MorphAString(*v8::Utils::OpenHandle(*rhs), &ascii_resource, &uc16_resource);