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1 /*
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2 * Copyright 2000-2004 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 // The following two classes are used to represent 'sizes' and 'offsets' in the VM;
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26 // they serve as 'unit' types. ByteSize is used for sizes measured in bytes, while
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27 // WordSize is used for sizes measured in machine words (i.e., 32bit or 64bit words
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28 // depending on platform).
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29 //
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30 // The classes are defined with friend functions operating on them instead of member
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31 // functions so that they (the classes) can be re-#define'd to int types in optimized
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32 // mode. This allows full type checking and maximum safety in debug mode, and full
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33 // optimizations (constant folding) and zero overhead (time and space wise) in the
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34 // optimized build (some compilers do not optimize one-element value classes but
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35 // instead create an object in memory - thus the overhead may be significant).
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36 //
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37 // Note: 1) DO NOT add new overloaded friend functions that do not have a unique function
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38 // function name but require signature types for resolution. This will not work
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39 // in optimized mode as both, ByteSize and WordSize are mapped to the same type
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40 // and thus the distinction would not be possible anymore (=> compiler errors).
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41 //
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42 // 2) DO NOT add non-static member functions as they cannot be mapped so something
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43 // compilable in the optimized build. Static member functions could be added
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44 // but require a corresponding class definition in the optimized build.
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45 //
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46 // These classes should help doing a transition from (currently) word-size based offsets
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47 // to byte-size based offsets in the VM (this will be important if we desire to pack
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48 // objects more densely in the VM for 64bit machines). Such a transition should proceed
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49 // in two steps to minimize the risk of introducing hard-to-find bugs:
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50 //
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51 // a) first transition the whole VM into a form where all sizes are strongly typed
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52 // b) change all WordSize's to ByteSize's where desired and fix the compilation errors
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53
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54
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55 #ifdef ASSERT
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56
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57 class ByteSize VALUE_OBJ_CLASS_SPEC {
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58 private:
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59 int _size;
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60
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61 // Note: This constructor must be private to avoid implicit conversions!
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62 ByteSize(int size) { _size = size; }
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63
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64 public:
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65 // constructors
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66 inline friend ByteSize in_ByteSize(int size);
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67
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68 // accessors
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69 inline friend int in_bytes(ByteSize x);
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70
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71 // operators
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72 friend ByteSize operator + (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) + in_bytes(y)); }
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73 friend ByteSize operator - (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) - in_bytes(y)); }
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74 friend ByteSize operator * (ByteSize x, int y) { return ByteSize(in_bytes(x) * y ); }
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75
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76 // comparison
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77 friend bool operator == (ByteSize x, ByteSize y) { return in_bytes(x) == in_bytes(y); }
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78 friend bool operator != (ByteSize x, ByteSize y) { return in_bytes(x) != in_bytes(y); }
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79 friend bool operator < (ByteSize x, ByteSize y) { return in_bytes(x) < in_bytes(y); }
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80 friend bool operator <= (ByteSize x, ByteSize y) { return in_bytes(x) <= in_bytes(y); }
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81 friend bool operator > (ByteSize x, ByteSize y) { return in_bytes(x) > in_bytes(y); }
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82 friend bool operator >= (ByteSize x, ByteSize y) { return in_bytes(x) >= in_bytes(y); }
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83 };
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84
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85 inline ByteSize in_ByteSize(int size) { return ByteSize(size); }
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86 inline int in_bytes(ByteSize x) { return x._size; }
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87
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88
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89 class WordSize VALUE_OBJ_CLASS_SPEC {
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90 private:
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91 int _size;
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92
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93 // Note: This constructor must be private to avoid implicit conversions!
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94 WordSize(int size) { _size = size; }
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95
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96 public:
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97 // constructors
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98 inline friend WordSize in_WordSize(int size);
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99
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100 // accessors
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101 inline friend int in_words(WordSize x);
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102
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103 // operators
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104 friend WordSize operator + (WordSize x, WordSize y) { return WordSize(in_words(x) + in_words(y)); }
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105 friend WordSize operator - (WordSize x, WordSize y) { return WordSize(in_words(x) - in_words(y)); }
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106 friend WordSize operator * (WordSize x, int y) { return WordSize(in_words(x) * y ); }
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107
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108 // comparison
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109 friend bool operator == (WordSize x, WordSize y) { return in_words(x) == in_words(y); }
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110 friend bool operator != (WordSize x, WordSize y) { return in_words(x) != in_words(y); }
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111 friend bool operator < (WordSize x, WordSize y) { return in_words(x) < in_words(y); }
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112 friend bool operator <= (WordSize x, WordSize y) { return in_words(x) <= in_words(y); }
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113 friend bool operator > (WordSize x, WordSize y) { return in_words(x) > in_words(y); }
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114 friend bool operator >= (WordSize x, WordSize y) { return in_words(x) >= in_words(y); }
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115 };
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116
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117 inline WordSize in_WordSize(int size) { return WordSize(size); }
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118 inline int in_words(WordSize x) { return x._size; }
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119
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120
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121 #else // ASSERT
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122
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123 // The following definitions must match the corresponding friend declarations
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124 // in the Byte/WordSize classes if they are typedef'ed to be int. This will
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125 // be the case in optimized mode to ensure zero overhead for these types.
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126 //
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127 // Note: If a compiler does not inline these function calls away, one may
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128 // want to use #define's to make sure full optimization (constant
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129 // folding in particular) is possible.
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130
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131 typedef int ByteSize;
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132 inline ByteSize in_ByteSize(int size) { return size; }
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133 inline int in_bytes (ByteSize x) { return x; }
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134
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135 typedef int WordSize;
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136 inline WordSize in_WordSize(int size) { return size; }
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137 inline int in_words (WordSize x) { return x; }
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138
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139 #endif // ASSERT
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140
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141
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142 // Use the following #define to get C++ field member offsets
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143
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144 #define byte_offset_of(klass,field) in_ByteSize((int)offset_of(klass, field))
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