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comparison src/share/vm/utilities/sizes.hpp @ 0:a61af66fc99e jdk7-b24

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author duke
date Sat, 01 Dec 2007 00:00:00 +0000
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1 /*
2 * Copyright 2000-2004 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
24
25 // The following two classes are used to represent 'sizes' and 'offsets' in the VM;
26 // they serve as 'unit' types. ByteSize is used for sizes measured in bytes, while
27 // WordSize is used for sizes measured in machine words (i.e., 32bit or 64bit words
28 // depending on platform).
29 //
30 // The classes are defined with friend functions operating on them instead of member
31 // functions so that they (the classes) can be re-#define'd to int types in optimized
32 // mode. This allows full type checking and maximum safety in debug mode, and full
33 // optimizations (constant folding) and zero overhead (time and space wise) in the
34 // optimized build (some compilers do not optimize one-element value classes but
35 // instead create an object in memory - thus the overhead may be significant).
36 //
37 // Note: 1) DO NOT add new overloaded friend functions that do not have a unique function
38 // function name but require signature types for resolution. This will not work
39 // in optimized mode as both, ByteSize and WordSize are mapped to the same type
40 // and thus the distinction would not be possible anymore (=> compiler errors).
41 //
42 // 2) DO NOT add non-static member functions as they cannot be mapped so something
43 // compilable in the optimized build. Static member functions could be added
44 // but require a corresponding class definition in the optimized build.
45 //
46 // These classes should help doing a transition from (currently) word-size based offsets
47 // to byte-size based offsets in the VM (this will be important if we desire to pack
48 // objects more densely in the VM for 64bit machines). Such a transition should proceed
49 // in two steps to minimize the risk of introducing hard-to-find bugs:
50 //
51 // a) first transition the whole VM into a form where all sizes are strongly typed
52 // b) change all WordSize's to ByteSize's where desired and fix the compilation errors
53
54
55 #ifdef ASSERT
56
57 class ByteSize VALUE_OBJ_CLASS_SPEC {
58 private:
59 int _size;
60
61 // Note: This constructor must be private to avoid implicit conversions!
62 ByteSize(int size) { _size = size; }
63
64 public:
65 // constructors
66 inline friend ByteSize in_ByteSize(int size);
67
68 // accessors
69 inline friend int in_bytes(ByteSize x);
70
71 // operators
72 friend ByteSize operator + (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) + in_bytes(y)); }
73 friend ByteSize operator - (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) - in_bytes(y)); }
74 friend ByteSize operator * (ByteSize x, int y) { return ByteSize(in_bytes(x) * y ); }
75
76 // comparison
77 friend bool operator == (ByteSize x, ByteSize y) { return in_bytes(x) == in_bytes(y); }
78 friend bool operator != (ByteSize x, ByteSize y) { return in_bytes(x) != in_bytes(y); }
79 friend bool operator < (ByteSize x, ByteSize y) { return in_bytes(x) < in_bytes(y); }
80 friend bool operator <= (ByteSize x, ByteSize y) { return in_bytes(x) <= in_bytes(y); }
81 friend bool operator > (ByteSize x, ByteSize y) { return in_bytes(x) > in_bytes(y); }
82 friend bool operator >= (ByteSize x, ByteSize y) { return in_bytes(x) >= in_bytes(y); }
83 };
84
85 inline ByteSize in_ByteSize(int size) { return ByteSize(size); }
86 inline int in_bytes(ByteSize x) { return x._size; }
87
88
89 class WordSize VALUE_OBJ_CLASS_SPEC {
90 private:
91 int _size;
92
93 // Note: This constructor must be private to avoid implicit conversions!
94 WordSize(int size) { _size = size; }
95
96 public:
97 // constructors
98 inline friend WordSize in_WordSize(int size);
99
100 // accessors
101 inline friend int in_words(WordSize x);
102
103 // operators
104 friend WordSize operator + (WordSize x, WordSize y) { return WordSize(in_words(x) + in_words(y)); }
105 friend WordSize operator - (WordSize x, WordSize y) { return WordSize(in_words(x) - in_words(y)); }
106 friend WordSize operator * (WordSize x, int y) { return WordSize(in_words(x) * y ); }
107
108 // comparison
109 friend bool operator == (WordSize x, WordSize y) { return in_words(x) == in_words(y); }
110 friend bool operator != (WordSize x, WordSize y) { return in_words(x) != in_words(y); }
111 friend bool operator < (WordSize x, WordSize y) { return in_words(x) < in_words(y); }
112 friend bool operator <= (WordSize x, WordSize y) { return in_words(x) <= in_words(y); }
113 friend bool operator > (WordSize x, WordSize y) { return in_words(x) > in_words(y); }
114 friend bool operator >= (WordSize x, WordSize y) { return in_words(x) >= in_words(y); }
115 };
116
117 inline WordSize in_WordSize(int size) { return WordSize(size); }
118 inline int in_words(WordSize x) { return x._size; }
119
120
121 #else // ASSERT
122
123 // The following definitions must match the corresponding friend declarations
124 // in the Byte/WordSize classes if they are typedef'ed to be int. This will
125 // be the case in optimized mode to ensure zero overhead for these types.
126 //
127 // Note: If a compiler does not inline these function calls away, one may
128 // want to use #define's to make sure full optimization (constant
129 // folding in particular) is possible.
130
131 typedef int ByteSize;
132 inline ByteSize in_ByteSize(int size) { return size; }
133 inline int in_bytes (ByteSize x) { return x; }
134
135 typedef int WordSize;
136 inline WordSize in_WordSize(int size) { return size; }
137 inline int in_words (WordSize x) { return x; }
138
139 #endif // ASSERT
140
141
142 // Use the following #define to get C++ field member offsets
143
144 #define byte_offset_of(klass,field) in_ByteSize((int)offset_of(klass, field))