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24
25#ifndef SHARE_UTILITIES_SIZES_HPP
26#define SHARE_UTILITIES_SIZES_HPP
27
28#include "utilities/globalDefinitions.hpp"
29
30// The following two classes are used to represent 'sizes' and 'offsets' in the VM;
31// they serve as 'unit' types. ByteSize is used for sizes measured in bytes, while
32// WordSize is used for sizes measured in machine words (i.e., 32bit or 64bit words
33// depending on platform).
34//
35// The classes are defined with friend functions operating on them instead of member
36// functions so that they (the classes) can be re-#define'd to int types in optimized
37// mode. This allows full type checking and maximum safety in debug mode, and full
38// optimizations (constant folding) and zero overhead (time and space wise) in the
39// optimized build (some compilers do not optimize one-element value classes but
40// instead create an object in memory - thus the overhead may be significant).
41//
42// Note: 1) DO NOT add new overloaded friend functions that do not have a unique function
43// function name but require signature types for resolution. This will not work
44// in optimized mode as both, ByteSize and WordSize are mapped to the same type
45// and thus the distinction would not be possible anymore (=> compiler errors).
46//
47// 2) DO NOT add non-static member functions as they cannot be mapped so something
48// compilable in the optimized build. Static member functions could be added
49// but require a corresponding class definition in the optimized build.
50//
51// These classes should help doing a transition from (currently) word-size based offsets
52// to byte-size based offsets in the VM (this will be important if we desire to pack
53// objects more densely in the VM for 64bit machines). Such a transition should proceed
54// in two steps to minimize the risk of introducing hard-to-find bugs:
55//
56// a) first transition the whole VM into a form where all sizes are strongly typed
57// b) change all WordSize's to ByteSize's where desired and fix the compilation errors
58
59
60#ifdef ASSERT
61
62class ByteSize {
63 private:
64 int _size;
65
66 // Note: This constructor must be private to avoid implicit conversions!
67 ByteSize(int size) { _size = size; }
68
69 public:
70 // constructors
71 inline friend ByteSize in_ByteSize(int size);
72
73 // accessors
74 inline friend int in_bytes(ByteSize x);
75
76 // operators
77 friend ByteSize operator + (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) + in_bytes(y)); }
78 friend ByteSize operator - (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) - in_bytes(y)); }
79 friend ByteSize operator * (ByteSize x, int y) { return ByteSize(in_bytes(x) * y ); }
80
81 // comparison
82 friend bool operator == (ByteSize x, ByteSize y) { return in_bytes(x) == in_bytes(y); }
83 friend bool operator != (ByteSize x, ByteSize y) { return in_bytes(x) != in_bytes(y); }
84 friend bool operator < (ByteSize x, ByteSize y) { return in_bytes(x) < in_bytes(y); }
85 friend bool operator <= (ByteSize x, ByteSize y) { return in_bytes(x) <= in_bytes(y); }
86 friend bool operator > (ByteSize x, ByteSize y) { return in_bytes(x) > in_bytes(y); }
87 friend bool operator >= (ByteSize x, ByteSize y) { return in_bytes(x) >= in_bytes(y); }
88};
89
90inline ByteSize in_ByteSize(int size) { return ByteSize(size); }
91inline int in_bytes(ByteSize x) { return x._size; }
92
93
94class WordSize {
95 private:
96 int _size;
97
98 // Note: This constructor must be private to avoid implicit conversions!
99 WordSize(int size) { _size = size; }
100
101 public:
102 // constructors
103 inline friend WordSize in_WordSize(int size);
104
105 // accessors
106 inline friend int in_words(WordSize x);
107
108 // operators
109 friend WordSize operator + (WordSize x, WordSize y) { return WordSize(in_words(x) + in_words(y)); }
110 friend WordSize operator - (WordSize x, WordSize y) { return WordSize(in_words(x) - in_words(y)); }
111 friend WordSize operator * (WordSize x, int y) { return WordSize(in_words(x) * y ); }
112
113 // comparison
114 friend bool operator == (WordSize x, WordSize y) { return in_words(x) == in_words(y); }
115 friend bool operator != (WordSize x, WordSize y) { return in_words(x) != in_words(y); }
116 friend bool operator < (WordSize x, WordSize y) { return in_words(x) < in_words(y); }
117 friend bool operator <= (WordSize x, WordSize y) { return in_words(x) <= in_words(y); }
118 friend bool operator > (WordSize x, WordSize y) { return in_words(x) > in_words(y); }
119 friend bool operator >= (WordSize x, WordSize y) { return in_words(x) >= in_words(y); }
120};
121
122inline WordSize in_WordSize(int size) { return WordSize(size); }
123inline int in_words(WordSize x) { return x._size; }
124
125
126#else // ASSERT
127
128// The following definitions must match the corresponding friend declarations
129// in the Byte/WordSize classes if they are typedef'ed to be int. This will
130// be the case in optimized mode to ensure zero overhead for these types.
131//
132// Note: If a compiler does not inline these function calls away, one may
133// want to use #define's to make sure full optimization (constant
134// folding in particular) is possible.
135
136typedef int ByteSize;
137inline ByteSize in_ByteSize(int size) { return size; }
138inline int in_bytes (ByteSize x) { return x; }
139
140typedef int WordSize;
141inline WordSize in_WordSize(int size) { return size; }
142inline int in_words (WordSize x) { return x; }
143
144#endif // ASSERT
145
146
147// Use the following #define to get C++ field member offsets
148
149#define byte_offset_of(klass,field) in_ByteSize((int)offset_of(klass, field))
150
151#endif // SHARE_UTILITIES_SIZES_HPP
152