1 /*
   2  * Copyright (c) 2000, 2018, 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 
  25 #ifndef SHARE_VM_UTILITIES_SIZES_HPP
  26 #define SHARE_VM_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 
  62 class 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 
  90 inline ByteSize in_ByteSize(int size) { return ByteSize(size); }
  91 inline int      in_bytes(ByteSize x)  { return x._size; }
  92 
  93 
  94 class 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 
 122 inline WordSize in_WordSize(int size) { return WordSize(size); }
 123 inline 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 
 136 typedef int ByteSize;
 137 inline ByteSize in_ByteSize(int size)                 { return size; }
 138 inline int      in_bytes   (ByteSize x)               { return x; }
 139 
 140 typedef int WordSize;
 141 inline WordSize in_WordSize(int size)                 { return size; }
 142 inline 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_VM_UTILITIES_SIZES_HPP