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 * accompanied this code).

 *

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#ifndef SHARE_VM_UTILITIES_SIZES_HPP

#define SHARE_VM_UTILITIES_SIZES_HPP

#include "utilities/globalDefinitions.hpp"

// The following two classes are used to represent 'sizes' and 'offsets' in the VM;

// they serve as 'unit' types. ByteSize is used for sizes measured in bytes, while

// WordSize is used for sizes measured in machine words (i.e., 32bit or 64bit words

// depending on platform).

//

// The classes are defined with friend functions operating on them instead of member

// functions so that they (the classes) can be re-#define'd to int types in optimized

// mode. This allows full type checking and maximum safety in debug mode, and full

// optimizations (constant folding) and zero overhead (time and space wise) in the

// optimized build (some compilers do not optimize one-element value classes but

// instead create an object in memory - thus the overhead may be significant).

//

// Note: 1) DO NOT add new overloaded friend functions that do not have a unique function

//          function name but require signature types for resolution. This will not work

//          in optimized mode as both, ByteSize and WordSize are mapped to the same type

//          and thus the distinction would not be possible anymore (=> compiler errors).

//

//       2) DO NOT add non-static member functions as they cannot be mapped so something

//          compilable in the optimized build. Static member functions could be added

//          but require a corresponding class definition in the optimized build.

//

// These classes should help doing a transition from (currently) word-size based offsets

// to byte-size based offsets in the VM (this will be important if we desire to pack

// objects more densely in the VM for 64bit machines). Such a transition should proceed

// in two steps to minimize the risk of introducing hard-to-find bugs:

//

// a) first transition the whole VM into a form where all sizes are strongly typed

// b) change all WordSize's to ByteSize's where desired and fix the compilation errors

#ifdef ASSERT

class ByteSize {

 private:

  int _size;

  // Note: This constructor must be private to avoid implicit conversions!

  ByteSize(int size)                                  { _size = size; }

 public:

  // constructors

  inline friend ByteSize in_ByteSize(int size);

  // accessors

  inline friend int in_bytes(ByteSize x);

  // operators

  friend ByteSize operator + (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) + in_bytes(y)); }

  friend ByteSize operator - (ByteSize x, ByteSize y) { return ByteSize(in_bytes(x) - in_bytes(y)); }

  friend ByteSize operator * (ByteSize x, int      y) { return ByteSize(in_bytes(x) * y          ); }

  // comparison

  friend bool operator == (ByteSize x, ByteSize y)    { return in_bytes(x) == in_bytes(y); }

  friend bool operator != (ByteSize x, ByteSize y)    { return in_bytes(x) != in_bytes(y); }

  friend bool operator <  (ByteSize x, ByteSize y)    { return in_bytes(x) <  in_bytes(y); }

  friend bool operator <= (ByteSize x, ByteSize y)    { return in_bytes(x) <= in_bytes(y); }

  friend bool operator >  (ByteSize x, ByteSize y)    { return in_bytes(x) >  in_bytes(y); }

  friend bool operator >= (ByteSize x, ByteSize y)    { return in_bytes(x) >= in_bytes(y); }

};

inline ByteSize in_ByteSize(int size) { return ByteSize(size); }

inline int      in_bytes(ByteSize x)  { return x._size; }

class WordSize {

 private:

  int _size;

  // Note: This constructor must be private to avoid implicit conversions!

  WordSize(int size)                                  { _size = size; }

 public:

  // constructors

  inline friend WordSize in_WordSize(int size);

  // accessors

  inline friend int in_words(WordSize x);

  // operators

  friend WordSize operator + (WordSize x, WordSize y) { return WordSize(in_words(x) + in_words(y)); }

  friend WordSize operator - (WordSize x, WordSize y) { return WordSize(in_words(x) - in_words(y)); }

  friend WordSize operator * (WordSize x, int      y) { return WordSize(in_words(x) * y          ); }

  // comparison

  friend bool operator == (WordSize x, WordSize y)    { return in_words(x) == in_words(y); }

  friend bool operator != (WordSize x, WordSize y)    { return in_words(x) != in_words(y); }

  friend bool operator <  (WordSize x, WordSize y)    { return in_words(x) <  in_words(y); }

  friend bool operator <= (WordSize x, WordSize y)    { return in_words(x) <= in_words(y); }

  friend bool operator >  (WordSize x, WordSize y)    { return in_words(x) >  in_words(y); }

  friend bool operator >= (WordSize x, WordSize y)    { return in_words(x) >= in_words(y); }

};

inline WordSize in_WordSize(int size) { return WordSize(size); }

inline int      in_words(WordSize x)  { return x._size; }

#else // ASSERT

// The following definitions must match the corresponding friend declarations

// in the Byte/WordSize classes if they are typedef'ed to be int. This will

// be the case in optimized mode to ensure zero overhead for these types.

//

// Note: If a compiler does not inline these function calls away, one may

//       want to use #define's to make sure full optimization (constant

//       folding in particular) is possible.

typedef int ByteSize;

inline ByteSize in_ByteSize(int size)                 { return size; }

inline int      in_bytes   (ByteSize x)               { return x; }

typedef int WordSize;

inline WordSize in_WordSize(int size)                 { return size; }

inline int      in_words   (WordSize x)               { return x; }

#endif // ASSERT

// Use the following #define to get C++ field member offsets

#define byte_offset_of(klass,field)   in_ByteSize((int)offset_of(klass, field))

#endif // SHARE_VM_UTILITIES_SIZES_HPP