1 /*
2 * Copyright (c) 2017, 2019, 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_ZFORWARDINGENTRY_HPP
25 #define SHARE_GC_Z_ZFORWARDINGENTRY_HPP
26
27 #include "gc/z/zBitField.hpp"
28 #include "memory/allocation.hpp"
29 #include "metaprogramming/primitiveConversions.hpp"
30
31 //
32 // Forwarding entry layout
33 // -----------------------
34 //
35 // 6 4 4
36 // 3 6 5 1 0
37 // +--------------------+--------------------------------------------------+-+
38 // |11111111 11111111 11|111111 11111111 11111111 11111111 11111111 1111111|1|
39 // +--------------------+--------------------------------------------------+-+
40 // | | |
41 // | | 0-0 Populated Flag (1-bits) *
42 // | |
43 // | * 45-1 To Object Offset (45-bits)
44 // |
45 // * 63-46 From Object Index (18-bits)
46 //
47
48 class ZForwardingEntry {
49 friend class PrimitiveConversions;
50
51 private:
52 typedef ZBitField<uint64_t, bool, 0, 1> field_populated;
53 typedef ZBitField<uint64_t, size_t, 1, 45> field_to_offset;
54 typedef ZBitField<uint64_t, size_t, 46, 18> field_from_index;
55
56 uint64_t _entry;
57
58 public:
59 ZForwardingEntry() :
60 _entry(0) {}
61
62 ZForwardingEntry(size_t from_index, size_t to_offset) :
63 _entry(field_populated::encode(true) |
64 field_to_offset::encode(to_offset) |
65 field_from_index::encode(from_index)) {}
66
67 bool populated() const {
68 return field_populated::decode(_entry);
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 ZForwardingEntry
81 template <>
82 struct PrimitiveConversions::Translate<ZForwardingEntry> : public TrueType {
83 typedef ZForwardingEntry 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 ZForwardingEntry entry;
92 entry._entry = d;
93 return entry;
94 }
95 };
96
97 #endif // SHARE_GC_Z_ZFORWARDINGENTRY_HPP