/*

 * Copyright (c) 2017, 2019, 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

 * questions.

 */

#ifndef SHARE_GC_Z_ZFORWARDINGENTRY_HPP

#define SHARE_GC_Z_ZFORWARDINGENTRY_HPP

#include "gc/z/zBitField.hpp"

#include "memory/allocation.hpp"

#include "metaprogramming/primitiveConversions.hpp"

//

// Forwarding entry layout

// -----------------------

//

//   6                      4 4                                             0

//   3                      2 1                                             0

//  +------------------------+-----------------------------------------------+

//  |11111111 11111111 111111|11 11111111 11111111 11111111 11111111 11111111|

//  +------------------------+-----------------------------------------------+

//  |                        |

//  |                        * 41-0 To Object Offset (42-bits)

//  |

//  * 63-42 From Object Index (22-bits)

//

class ZForwardingEntry {

  friend struct PrimitiveConversions;

private:

  typedef ZBitField<uint64_t, size_t, 0,  42> field_to_offset;

  typedef ZBitField<uint64_t, size_t, 42, 22> field_from_index;

  uint64_t _entry;

  static uintptr_t empty() {

    return (uintptr_t)-1;

  }

public:

  ZForwardingEntry() :

      _entry(empty()) {}

  ZForwardingEntry(size_t from_index, size_t to_offset) :

      _entry(field_from_index::encode(from_index) |

             field_to_offset::encode(to_offset)) {}

  bool is_empty() const {

    return _entry == empty();

  }

  size_t to_offset() const {

    return field_to_offset::decode(_entry);

  }

  size_t from_index() const {

    return field_from_index::decode(_entry);

  }

};

// Needed to allow atomic operations on ZForwardingEntry

template <>

struct PrimitiveConversions::Translate<ZForwardingEntry> : public TrueType {

  typedef ZForwardingEntry Value;

  typedef uint64_t         Decayed;

  static Decayed decay(Value v) {

    return v._entry;

  }

  static Value recover(Decayed d) {

    ZForwardingEntry entry;

    entry._entry = d;

    return entry;

  }

};

#endif // SHARE_GC_Z_ZFORWARDINGENTRY_HPP