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
  31 namespace JSC {
  32
  33 class ArrayBuffer;
  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 offsetOfArrayBuffer() { return OBJECT_OFFSETOF(IndexingHeader, u.typedArray.buffer); }
  48     static ptrdiff_t offsetOfPublicLength() { return OBJECT_OFFSETOF(IndexingHeader, u.lengths.publicLength); }
  49     static ptrdiff_t offsetOfVectorLength() { return OBJECT_OFFSETOF(IndexingHeader, u.lengths.vectorLength); }
  50
  51     IndexingHeader()
  52     {
  53         u.lengths.publicLength = 0;
  54         u.lengths.vectorLength = 0;
  55     }
  56
  57     uint32_t vectorLength() const { return u.lengths.vectorLength; }
  58
  59     void setVectorLength(uint32_t length)
  60     {
  61         RELEASE_ASSERT(length <= maximumLength);
  62         u.lengths.vectorLength = length;
  63     }
  64
  65     uint32_t publicLength() const { return u.lengths.publicLength; }
  66     void setPublicLength(uint32_t auxWord) { u.lengths.publicLength = auxWord; }
  67
  68     ArrayBuffer* arrayBuffer() { return u.typedArray.buffer; }
  69     void setArrayBuffer(ArrayBuffer* buffer) { u.typedArray.buffer = buffer; }
  70
  71     static IndexingHeader* from(Butterfly* butterfly)
  72     {
  73         return reinterpret_cast<IndexingHeader*>(butterfly) - 1;
  74     }
  75
  76     static const IndexingHeader* from(const Butterfly* butterfly)
  77     {
  78         return reinterpret_cast<const IndexingHeader*>(butterfly) - 1;
  79     }
  80
  81     static IndexingHeader* from(ArrayStorage* arrayStorage)
  82     {
  83         return const_cast<IndexingHeader*>(from(const_cast<const ArrayStorage*>(arrayStorage)));
  84     }
  85
  86     static const IndexingHeader* from(const ArrayStorage* arrayStorage)
  87     {
  88         return reinterpret_cast<const IndexingHeader*>(arrayStorage) - 1;
  89     }
  90
  91     static IndexingHeader* fromEndOf(PropertyStorage propertyStorage)
  92     {
  93         return reinterpret_cast<IndexingHeader*>(propertyStorage);
  94     }
  95
  96     PropertyStorage propertyStorage()
  97     {
  98         return reinterpret_cast_ptr<PropertyStorage>(this);
  99     }
 100
 101     ConstPropertyStorage propertyStorage() const
 102     {
 103         return reinterpret_cast_ptr<ConstPropertyStorage>(this);
 104     }
 105
 106     ArrayStorage* arrayStorage()
 107     {
 108         return reinterpret_cast<ArrayStorage*>(this + 1);
 109     }
 110
 111     Butterfly* butterfly()
 112     {
 113         return reinterpret_cast<Butterfly*>(this + 1);
 114     }
 115
 116     // These methods are not standalone in the sense that they cannot be
 117     // used on a copy of the IndexingHeader.
 118     size_t preCapacity(Structure*);
 119     size_t indexingPayloadSizeInBytes(Structure*);
 120
 121 private:
 122     friend class LLIntOffsetsExtractor;
 123
 124     union {
 125         struct {
 126             uint32_t 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).
 127             uint32_t vectorLength; // The length of the indexed property storage. The actual size of the storage depends on this, and the type.
 128         } lengths;
 129
 130         struct {
 131             ArrayBuffer* buffer;
 132         } typedArray;
 133     } u;
 134 };
 135
 136 } // namespace JSC
 137
 138 #endif // IndexingHeader_h
 139