1 /*

     2  * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.

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

     4  *

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

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

     7  * published by the Free Software Foundation.

     8  *

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

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

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

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

    13  * accompanied this code).

    14  *

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

    16  * 2 along with this work; if not, write to the Free Software Foundation,

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

    18  *

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

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

    21  * questions.

    22  */

    23 

    24 #ifndef SHARE_GC_Z_ZFORWARDINGTABLEENTRY_HPP

    25 #define SHARE_GC_Z_ZFORWARDINGTABLEENTRY_HPP

    26 

    27 #include "gc/z/zBitField.hpp"

    28 #include "memory/allocation.hpp"

    29 #include "metaprogramming/primitiveConversions.hpp"

    30 

    31 //

    32 // Forwarding table entry layout

    33 // -----------------------------

    34 //

    35 //   6                      4 4                                             0

    36 //   3                      2 1                                             0

    37 //  +------------------------+-----------------------------------------------+

    38 //  |11111111 11111111 111111|11 11111111 11111111 11111111 11111111 11111111|

    39 //  +------------------------+-----------------------------------------------+

    40 //  |                        |

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

    42 //  |

    43 //  * 63-42 From Object Index (22-bits)

    44 //

    45 

    46 class ZForwardingTableEntry {

    47   friend struct PrimitiveConversions;

    48 

    49 private:

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

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

    52 

    53   uint64_t _entry;

    54 

    55   static uintptr_t empty() {

    56     return (uintptr_t)-1;

    57   }

    58 

    59 public:

    60   ZForwardingTableEntry() :

    61       _entry(empty()) {}

    62 

    63   ZForwardingTableEntry(size_t from_index, size_t to_offset) :

    64       _entry(field_from_index::encode(from_index) |

    65              field_to_offset::encode(to_offset)) {}

    66 

    67   bool is_empty() const {

    68     return _entry == empty();

    69   }

    70 

    71   size_t to_offset() const {

    72     return field_to_offset::decode(_entry);

    73   }

    74 

    75   size_t from_index() const {

    76     return field_from_index::decode(_entry);

    77   }

    78 };

    79 

    80 // Needed to allow atomic operations on ZForwardingTableEntry

    81 template <>

    82 struct PrimitiveConversions::Translate<ZForwardingTableEntry> : public TrueType {

    83   typedef ZForwardingTableEntry Value;

    84   typedef uint64_t              Decayed;

    85 

    86   static Decayed decay(Value v) {

    87     return v._entry;

    88   }

    89 

    90   static Value recover(Decayed d) {

    91     ZForwardingTableEntry entry;

    92     entry._entry = d;

    93     return entry;

    94   }

    95 };

    96 

    97 #endif // SHARE_GC_Z_ZFORWARDINGTABLEENTRY_HPP