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 /*

  * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

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 #ifndef SHARE_VM_OOPS_ARRAYOOP_HPP

 #define SHARE_VM_OOPS_ARRAYOOP_HPP

 #include "memory/universe.inline.hpp"

 #include "oops/oop.hpp"

 // arrayOopDesc is the abstract baseclass for all arrays.  It doesn't

 // declare pure virtual to enforce this because that would allocate a vtbl

 // in each instance, which we don't want.

 // The layout of array Oops is:

 //

 //  markOop

 //  Klass*    // 32 bits if compressed but declared 64 in LP64.

 //  length    // shares klass memory or allocated after declared fields.

 class arrayOopDesc : public oopDesc {

   friend class VMStructs;

   // Interpreter/Compiler offsets

   // Header size computation.

   // The header is considered the oop part of this type plus the length.

   // Returns the aligned header_size_in_bytes.  This is not equivalent to

   // sizeof(arrayOopDesc) which should not appear in the code.

   static int header_size_in_bytes() {

     size_t hs = align_size_up(length_offset_in_bytes() + sizeof(int),

                               HeapWordSize);

 #ifdef ASSERT

     // make sure it isn't called before UseCompressedOops is initialized.

     static size_t arrayoopdesc_hs = 0;

     if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;

     assert(arrayoopdesc_hs == hs, "header size can't change");

 #endif // ASSERT

     return (int)hs;

   }

  public:

   // The _length field is not declared in C++.  It is allocated after the

   // declared nonstatic fields in arrayOopDesc if not compressed, otherwise

   // it occupies the second half of the _klass field in oopDesc.

   static int length_offset_in_bytes() {

     return UseCompressedKlassPointers ? klass_gap_offset_in_bytes() :

                                sizeof(arrayOopDesc);

   }

   // Returns the offset of the first element.

   static int base_offset_in_bytes(BasicType type) {

     return header_size(type) * HeapWordSize;

   }

   // Returns the address of the first element.

   void* base(BasicType type) const {

     return (void*) (((intptr_t) this) + base_offset_in_bytes(type));

   }

   // Tells whether index is within bounds.

   bool is_within_bounds(int index) const        { return 0 <= index && index < length(); }

   // Accessors for instance variable which is not a C++ declared nonstatic

   // field.

   int length() const {

     return *(int*)(((intptr_t)this) + length_offset_in_bytes());

   }

   void set_length(int length) {

     *(int*)(((intptr_t)this) + length_offset_in_bytes()) = length;

   }

   // Should only be called with constants as argument

   // (will not constant fold otherwise)

   // Returns the header size in words aligned to the requirements of the

   // array object type.

   static int header_size(BasicType type) {

     size_t typesize_in_bytes = header_size_in_bytes();

     return (int)(Universe::element_type_should_be_aligned(type)

       ? align_object_offset(typesize_in_bytes/HeapWordSize)

       : typesize_in_bytes/HeapWordSize);

   }

   // Return the maximum length of an array of BasicType.  The length can passed

   // to typeArrayOop::object_size(scale, length, header_size) without causing an

   // overflow. We also need to make sure that this will not overflow a size_t on

   // 32 bit platforms when we convert it to a byte size.

   static int32_t max_array_length(BasicType type) {

     assert(type >= 0 && type < T_CONFLICT, "wrong type");

     assert(type2aelembytes(type) != 0, "wrong type");

     const size_t max_element_words_per_size_t =

       align_size_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);

     const size_t max_elements_per_size_t =

       HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);

     if ((size_t)max_jint < max_elements_per_size_t) {

       // It should be ok to return max_jint here, but parts of the code

       // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for

       // passing around the size (in words) of an object. So, we need to avoid

       // overflowing an int when we add the header. See CRs 4718400 and 7110613.

       return align_size_down(max_jint - header_size(type), MinObjAlignment);

     }

     return (int32_t)max_elements_per_size_t;

   }

 // for unit testing

 #ifndef PRODUCT

   static bool check_max_length_overflow(BasicType type);

   static int32_t old_max_array_length(BasicType type);

   static void test_max_array_length();

 #endif

 };

 #endif // SHARE_VM_OOPS_ARRAYOOP_HPP