rc_string_base.h

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      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 83.  String::npos vs. string::max_size()
      if (__capacity > size_type(_S_max_size))
	std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));

      // The standard places no restriction on allocating more memory
      // than is strictly needed within this layer at the moment or as
      // requested by an explicit application call to reserve().

      // Many malloc implementations perform quite poorly when an
      // application attempts to allocate memory in a stepwise fashion
      // growing each allocation size by only 1 char.  Additionally,
      // it makes little sense to allocate less linear memory than the
      // natural blocking size of the malloc implementation.
      // Unfortunately, we would need a somewhat low-level calculation
      // with tuned parameters to get this perfect for any particular
      // malloc implementation.  Fortunately, generalizations about
      // common features seen among implementations seems to suffice.

      // __pagesize need not match the actual VM page size for good
      // results in practice, thus we pick a common value on the low
      // side.  __malloc_header_size is an estimate of the amount of
      // overhead per memory allocation (in practice seen N * sizeof
      // (void*) where N is 0, 2 or 4).  According to folklore,
      // picking this value on the high side is better than
      // low-balling it (especially when this algorithm is used with
      // malloc implementations that allocate memory blocks rounded up
      // to a size which is a power of 2).
      const size_type __pagesize = 4096;
      const size_type __malloc_header_size = 4 * sizeof(void*);

      // The below implements an exponential growth policy, necessary to
      // meet amortized linear time requirements of the library: see
      // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
      if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
	__capacity = 2 * __old_capacity;

      // NB: Need an array of char_type[__capacity], plus a terminating
      // null char_type() element, plus enough for the _Rep data structure,
      // plus sizeof(_Rep) - 1 to upper round to a size multiple of
      // sizeof(_Rep).
      // Whew. Seemingly so needy, yet so elemental.
      size_type __size = ((__capacity + 1) * sizeof(_CharT)
			  + 2 * sizeof(_Rep) - 1);

      const size_type __adj_size = __size + __malloc_header_size;
      if (__adj_size > __pagesize && __capacity > __old_capacity)
	{
	  const size_type __extra = __pagesize - __adj_size % __pagesize;
	  __capacity += __extra / sizeof(_CharT);
	  // Never allocate a string bigger than _S_max_size.
	  if (__capacity > size_type(_S_max_size))
	    __capacity = size_type(_S_max_size);
	  __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
	}

      // NB: Might throw, but no worries about a leak, mate: _Rep()
      // does not throw.
      _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
      _Rep* __p = new (__place) _Rep;
      __p->_M_info._M_capacity = __capacity;
      return __p;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    void
    __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    _M_destroy(const _Alloc& __a) throw ()
    {
      const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
				+ 2 * sizeof(_Rep) - 1);
      _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _CharT*
    __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    _M_clone(const _Alloc& __alloc, size_type __res)
    {
      // Requested capacity of the clone.
      const size_type __requested_cap = _M_info._M_length + __res;
      _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
				  __alloc);

      if (_M_info._M_length)
	_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);

      __r->_M_set_length(_M_info._M_length);
      return __r->_M_refdata();
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    __rc_string_base<_CharT, _Traits, _Alloc>::
    __rc_string_base(const _Alloc& __a)
    : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }

  template<typename _CharT, typename _Traits, typename _Alloc>
    __rc_string_base<_CharT, _Traits, _Alloc>::
    __rc_string_base(const __rc_string_base& __rcs)
    : _M_dataplus(__rcs._M_get_allocator(),
		  __rcs._M_grab(__rcs._M_get_allocator())) { }

  template<typename _CharT, typename _Traits, typename _Alloc>
    __rc_string_base<_CharT, _Traits, _Alloc>::
    __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
    : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }

  template<typename _CharT, typename _Traits, typename _Alloc>
    template<typename _InputIterator>
    __rc_string_base<_CharT, _Traits, _Alloc>::
    __rc_string_base(_InputIterator __beg, _InputIterator __end,
		     const _Alloc& __a)
    : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }

  template<typename _CharT, typename _Traits, typename _Alloc>
    void
    __rc_string_base<_CharT, _Traits, _Alloc>::
    _M_leak_hard()
    {
      if (_M_is_shared())
	_M_erase(0, 0);
      _M_set_leaked();
    }

  // NB: This is the special case for Input Iterators, used in
  // istreambuf_iterators, etc.
  // Input Iterators have a cost structure very different from
  // pointers, calling for a different coding style.
  template<typename _CharT, typename _Traits, typename _Alloc>
    template<typename _InIterator>
      _CharT*
      __rc_string_base<_CharT, _Traits, _Alloc>::
      _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
		   std::input_iterator_tag)
      {
	if (__beg == __end && __a == _Alloc())
	  return _S_empty_rep._M_refcopy();

	// Avoid reallocation for common case.
	_CharT __buf[128];
	size_type __len = 0;
	while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
	  {
	    __buf[__len++] = *__beg;
	    ++__beg;
	  }
	_Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
	_S_copy(__r->_M_refdata(), __buf, __len);
	try
	  {
	    while (__beg != __end)
	      {
		if (__len == __r->_M_info._M_capacity)
		  {
		    // Allocate more space.
		    _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
		    _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
		    __r->_M_destroy(__a);
		    __r = __another;
		  }
		__r->_M_refdata()[__len++] = *__beg;
		++__beg;
	      }
	  }
	catch(...)
	  {
	    __r->_M_destroy(__a);
	    __throw_exception_again;
	  }
	__r->_M_set_length(__len);
	return __r->_M_refdata();
      }

  template<typename _CharT, typename _Traits, typename _Alloc>
    template<typename _InIterator>
      _CharT*
      __rc_string_base<_CharT, _Traits, _Alloc>::
      _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
		   std::forward_iterator_tag)
      {
	if (__beg == __end && __a == _Alloc())
	  return _S_empty_rep._M_refcopy();

	// NB: Not required, but considered best practice.
	if (__builtin_expect(_S_is_null_pointer(__beg) && __beg != __end, 0))
	  std::__throw_logic_error(__N("__rc_string_base::"
				       "_S_construct NULL not valid"));

	const size_type __dnew = static_cast<size_type>(std::distance(__beg,
								      __end));
	// Check for out_of_range and length_error exceptions.
	_Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
	try
	  { _S_copy_chars(__r->_M_refdata(), __beg, __end); }
	catch(...)
	  {
	    __r->_M_destroy(__a);
	    __throw_exception_again;
	  }
	__r->_M_set_length(__dnew);
	return __r->_M_refdata();
      }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _CharT*
    __rc_string_base<_CharT, _Traits, _Alloc>::
    _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
    {
      if (__n == 0 && __a == _Alloc())
	return _S_empty_rep._M_refcopy();

      // Check for out_of_range and length_error exceptions.
      _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
      if (__n)
	_S_assign(__r->_M_refdata(), __n, __c);

      __r->_M_set_length(__n);
      return __r->_M_refdata();
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    void
    __rc_string_base<_CharT, _Traits, _Alloc>::
    _M_swap(__rc_string_base& __rcs)
    {
      if (_M_is_leaked())
	_M_set_sharable();
      if (__rcs._M_is_leaked())
	__rcs._M_set_sharable();
      
      _CharT* __tmp = _M_data();
      _M_data(__rcs._M_data());
      __rcs._M_data(__tmp);
      
      // NB: Implement Option 3 of DR 431 (see N1599).
      std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
						  __rcs._M_get_allocator());
    } 

  template<typename _CharT, typename _Traits, typename _Alloc>
    void
    __rc_string_base<_CharT, _Traits, _Alloc>::
    _M_assign(const __rc_string_base& __rcs)
    {
      if (_M_rep() != __rcs._M_rep())
	{
	  _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
	  _M_dispose();
	  _M_data(__tmp);
	}
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    void
    __rc_string_base<_CharT, _Traits, _Alloc>::
    _M_reserve(size_type __res)
    {
      // Make sure we don't shrink below the current size.
      if (__res < _M_length())
	__res = _M_length();
      
      if (__res != _M_capacity() || _M_is_shared())
	{
	  _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
					     __res - _M_length());
	  _M_dispose();
	  _M_data(__tmp);
	}
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    void
    __rc_string_base<_CharT, _Traits, _Alloc>::
    _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
	      size_type __len2)
    {
      const size_type __how_much = _M_length() - __pos - __len1;
      
      _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
				  _M_capacity(), _M_get_allocator());
      
      if (__pos)
	_S_copy(__r->_M_refdata(), _M_data(), __pos);
      if (__s && __len2)
	_S_copy(__r->_M_refdata() + __pos, __s, __len2);
      if (__how_much)
	_S_copy(__r->_M_refdata() + __pos + __len2,
		_M_data() + __pos + __len1, __how_much);
      
      _M_dispose();
      _M_data(__r->_M_refdata());
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    void
    __rc_string_base<_CharT, _Traits, _Alloc>::
    _M_erase(size_type __pos, size_type __n)
    {
      const size_type __new_size = _M_length() - __n;
      const size_type __how_much = _M_length() - __pos - __n;
      
      if (_M_is_shared())
	{
	  // Must reallocate.
	  _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
				      _M_get_allocator());

	  if (__pos)
	    _S_copy(__r->_M_refdata(), _M_data(), __pos);
	  if (__how_much)
	    _S_copy(__r->_M_refdata() + __pos,
		    _M_data() + __pos + __n, __how_much);

	  _M_dispose();
	  _M_data(__r->_M_refdata());
	}
      else if (__how_much && __n)
	{
	  // Work in-place.
	  _S_move(_M_data() + __pos,
		  _M_data() + __pos + __n, __how_much);
	}

      _M_rep()->_M_set_length(__new_size);      
    }

  template<>
    inline bool
    __rc_string_base<char, std::char_traits<char>,
		     std::allocator<char> >::
    _M_compare(const __rc_string_base& __rcs) const
    {
      if (_M_rep() == __rcs._M_rep())
	return true;
      return false;
    }

  template<>
    inline bool
    __rc_string_base<wchar_t, std::char_traits<wchar_t>,
		     std::allocator<wchar_t> >::
    _M_compare(const __rc_string_base& __rcs) const
    {
      if (_M_rep() == __rcs._M_rep())
	return true;
      return false;
    }
} // namespace __gnu_cxx

#endif /* _RC_STRING_BASE_H */