runtime/IndexingHeader.h

   1 /*
   2  * Copyright (C) 2012 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef IndexingHeader_h
  27 #define IndexingHeader_h
  28
  29 #include "PropertyStorage.h"
  30 #include <wtf/Platform.h>
  31
  32 namespace JSC {
  33
  34 class Butterfly;
  35 class LLIntOffsetsExtractor;
  36 class Structure;
  37 struct ArrayStorage;
  38
  39 class IndexingHeader {
  40 public:
  41     // Define the maximum storage vector length to be 2^32 / sizeof(JSValue) / 2 to ensure that
  42     // there is no risk of overflow.
  43     enum { maximumLength = 0x10000000 };
  44
  45     static ptrdiff_t offsetOfIndexingHeader() { return -static_cast<ptrdiff_t>(sizeof(IndexingHeader)); }
  46
  47     static ptrdiff_t offsetOfPublicLength() { return OBJECT_OFFSETOF(IndexingHeader, m_publicLength); }
  48     static ptrdiff_t offsetOfVectorLength() { return OBJECT_OFFSETOF(IndexingHeader, m_vectorLength); }
  49
  50     IndexingHeader()
  51         : m_publicLength(0)
  52         , m_vectorLength(0)
  53     {
  54     }
  55
  56     uint32_t vectorLength() const { return m_vectorLength; }
  57
  58     void setVectorLength(uint32_t length)
  59     {
  60         RELEASE_ASSERT(length <= maximumLength);
  61         m_vectorLength = length;
  62     }
  63
  64     uint32_t publicLength() { return m_publicLength; }
  65     void setPublicLength(uint32_t auxWord) { m_publicLength = auxWord; }
  66
  67     static IndexingHeader* from(Butterfly* butterfly)
  68     {
  69         return reinterpret_cast<IndexingHeader*>(butterfly) - 1;
  70     }
  71
  72     static const IndexingHeader* from(const Butterfly* butterfly)
  73     {
  74         return reinterpret_cast<const IndexingHeader*>(butterfly) - 1;
  75     }
  76
  77     static IndexingHeader* from(ArrayStorage* arrayStorage)
  78     {
  79         return reinterpret_cast<IndexingHeader*>(arrayStorage) - 1;
  80     }
  81
  82     static IndexingHeader* fromEndOf(PropertyStorage propertyStorage)
  83     {
  84         return reinterpret_cast<IndexingHeader*>(propertyStorage);
  85     }
  86
  87     PropertyStorage propertyStorage()
  88     {
  89         return reinterpret_cast_ptr<PropertyStorage>(this);
  90     }
  91
  92     ConstPropertyStorage propertyStorage() const
  93     {
  94         return reinterpret_cast_ptr<ConstPropertyStorage>(this);
  95     }
  96
  97     ArrayStorage* arrayStorage()
  98     {
  99         return reinterpret_cast<ArrayStorage*>(this + 1);
 100     }
 101
 102     Butterfly* butterfly()
 103     {
 104         return reinterpret_cast<Butterfly*>(this + 1);
 105     }
 106
 107     // These methods are not standalone in the sense that they cannot be
 108     // used on a copy of the IndexingHeader.
 109     size_t preCapacity(Structure*);
 110     size_t indexingPayloadSizeInBytes(Structure*);
 111
 112 private:
 113     friend class LLIntOffsetsExtractor;
 114
 115     uint32_t m_publicLength; // The meaning of this field depends on the array type, but for all JSArrays we rely on this being the publicly visible length (array.length).
 116     uint32_t m_vectorLength; // The length of the indexed property storage. The actual size of the storage depends on this, and the type.
 117 };
 118
 119 } // namespace JSC
 120
 121 #endif // IndexingHeader_h
 122