js/public/shadow/Object.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * Shadow definition of |JSObject| innards.  (|js::NativeObject| is more
   9  * accurate, but portions can sometimes be used in some non-native objects.)  Do
  10  * not use this directly!
  11  */
  12
  13 #ifndef js_shadow_Object_h
  14 #define js_shadow_Object_h
  15
  16 #include <stddef.h>  // size_t
  17
  18 #include "js/shadow/Shape.h"  // JS::shadow::Shape
  19 #include "js/Value.h"         // JS::Value
  20
  21 class JS_PUBLIC_API JSObject;
  22
  23 namespace JS {
  24
  25 class JS_PUBLIC_API Value;
  26
  27 namespace shadow {
  28
  29 /**
  30  * This layout is shared by all native objects. For non-native objects, the
  31  * shape may always be accessed safely, and other members may be as well,
  32  * depending on the object's specific layout.
  33  */
  34 struct Object {
  35   shadow::Shape* shape;
  36 #ifndef JS_64BIT
  37   uint32_t padding_;
  38 #endif
  39   Value* slots;
  40   void* _1;
  41
  42   static constexpr size_t MAX_FIXED_SLOTS = 16;
  43
  44   size_t numFixedSlots() const {
  45     return (shape->immutableFlags & shadow::Shape::FIXED_SLOTS_MASK) >>
  46            shadow::Shape::FIXED_SLOTS_SHIFT;
  47   }
  48
  49   Value* fixedSlots() const {
  50     auto address = reinterpret_cast<uintptr_t>(this);
  51     return reinterpret_cast<JS::Value*>(address + sizeof(shadow::Object));
  52   }
  53
  54   Value& slotRef(size_t slot) const {
  55     size_t nfixed = numFixedSlots();
  56     if (slot < nfixed) {
  57       return fixedSlots()[slot];
  58     }
  59     return slots[slot - nfixed];
  60   }
  61 };
  62
  63 }  // namespace shadow
  64
  65 }  // namespace JS
  66
  67 #endif  // js_shadow_Object_h