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 * 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

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 */

#include "memory/universe.hpp"

#include "oops/oop.hpp"

#include "utilities/align.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;

  friend class arrayOopDescTest;

  // 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_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;

  }

  // Check whether an element of a typeArrayOop with the given type must be

  // aligned 0 mod 8.  The typeArrayOop itself must be aligned at least this

  // strongly.

  static bool element_type_should_be_aligned(BasicType type) {

    return type == T_DOUBLE || type == T_LONG;

  }

 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 UseCompressedClassPointers ? 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. The elements in the array will not

  // relocate from this address until a subsequent thread transition.

  inline void* base(BasicType type) const;

  inline void* base_raw(BasicType type) const; // GC barrier invariant

  template <typename T>

  static T* obj_offset_to_raw(arrayOop obj, size_t offset_in_bytes, T* raw) {

    if (obj != NULL) {

      assert(raw == NULL, "either raw or in-heap");

      char* base = reinterpret_cast<char*>((void*) obj);

      raw = reinterpret_cast<T*>(base + offset_in_bytes);

    } else {

      assert(raw != NULL, "either raw or in-heap");

    }

    return raw;

  }

  // 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) {

    set_length((HeapWord*)this, length);

  }

  static void set_length(HeapWord* mem, int length) {

    *(int*)(((char*)mem) + 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)(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_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_down(max_jint - header_size(type), MinObjAlignment);

    }

    return (int32_t)max_elements_per_size_t;

  }

};