Changeset 51352 in webkit for trunk/JavaScriptCore/runtime/JSONObject.cpp

Timestamp:

Nov 24, 2009, 1:41:53 PM (16 years ago)

Author:

[email protected]

Message:

JSON.stringify performance on undefined is very poor
​https://bugs.webkit.org/show_bug.cgi?id=31839

Reviewed by Alexey Proskuryakov.

Switch from a UString to a Vector<UChar> when building
the JSON string, allowing us to safely remove the substr-copy
we otherwise did when unwinding an undefined property.

Also turns out to be a ~5% speedup on stringification.

File:

• trunk/JavaScriptCore/runtime/JSONObject.cpp (modified) (3 diffs)

trunk/JavaScriptCore/runtime/JSONObject.cpp

@@ -71 +71 @@
 
 private:
-    typedef UString StringBuilder;
+    class StringBuilder : public Vector<UChar> {
+    public:
+        using Vector<UChar>::append;
+
+        inline void append(const char* str)
+        {
+            size_t len = strlen(str);
+            reserveCapacity(size() + len);
+            for (size_t i = 0; i < len; i++)
+                Vector<UChar>::append(str[i]);
+        }
+
+        inline void append(const UString& str)
+        {
+            append(str.data(), str.size());
+        }
+    };
 
     class Holder {
@@ -270 +286 @@
         return jsNull();
 
-    return jsString(m_exec, result);
+    result.shrinkToFit();
+    size_t length = result.size();
+    return jsString(m_exec, UString(result.releaseBuffer(), length, false));
 }
 
@@ -587 +605 @@
             // In this case we don't want the separator and property name that we
             // already appended, so roll back.
-            builder = builder.substr(0, rollBackPoint);
+            builder.resize(rollBackPoint);
             break;
     }