Changeset 175172 in webkit

Timestamp:

Oct 24, 2014, 12:16:29 PM (10 years ago)

Author:

mark.lam@apple.com

Message:

Simplified IndexingType's hasAnyArrayStorage().
<​https://webkit.org/b/138051>

Reviewed by Michael Saboff.

IndexingType's hasAnyArrayStorage() currently does subtraction of ArrayStorageShape
with the purpose of making non-ArrayStorage types underflow (with that subtraction)
and have a result that exceeds SlowPutArrayStorageShape. What it is doing is
basically checking for a shape value that is greater equal to ArrayStorageShape.
We can just simplify the code as such.

Also added a comment to describe the structure of the bits in IndexingType.

• runtime/IndexingType.h:

(JSC::hasAnyArrayStorage):

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• runtime/IndexingType.h (modified) (3 diffs)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2014-10-24  Mark Lam  <mark.lam@apple.com>
+
+        Simplified IndexingType's hasAnyArrayStorage().
+        <https://webkit.org/b/138051>
+
+        Reviewed by Michael Saboff.
+
+        IndexingType's hasAnyArrayStorage() currently does subtraction of ArrayStorageShape
+        with the purpose of making non-ArrayStorage types underflow (with that subtraction)
+        and have a result that exceeds SlowPutArrayStorageShape.  What it is doing is
+        basically checking for a shape value that is greater equal to ArrayStorageShape.
+        We can just simplify the code as such.
+
+        Also added a comment to describe the structure of the bits in IndexingType.
+
+        * runtime/IndexingType.h:
+        (JSC::hasAnyArrayStorage):
+
 2014-10-23  Joseph Pecoraro  <pecoraro@apple.com>
 

trunk/Source/JavaScriptCore/runtime/IndexingType.h

@@ -1 +1 @@
 /*
- * Copyright (C) 2012 Apple Inc. All rights reserved.
+ * Copyright (C) 2012, 2014 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -31 +31 @@
 
 namespace JSC {
+
+/*
+    Structure of the IndexingType
+    =============================
+    Conceptually, the IndexingType looks like this:
+
+    struct IndexingType {
+        uint8_t isArray:1;                    // bit 0
+        uint8_t shape:4;                      // bit 1 - 4
+        uint8_t mayHaveIndexedAccessors:1;    // bit 5
+    };
+
+    The shape values (e.g. Int32Shape, ContiguousShape, etc) are an enumeration of
+    various shapes (though not necessarily sequential in terms of their values).
+    Hence, shape values are not bitwise exclusive with respect to each other.
+*/
 
 typedef uint8_t IndexingType;
@@ -129 +145 @@
 static inline bool hasAnyArrayStorage(IndexingType indexingType)
 {
-    return static_cast<uint8_t>((indexingType & IndexingShapeMask) - ArrayStorageShape) <= static_cast<uint8_t>(SlowPutArrayStorageShape - ArrayStorageShape);
+    return static_cast<uint8_t>(indexingType & IndexingShapeMask) >= ArrayStorageShape;
 }