basic_string.h

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// Components for manipulating sequences of characters -*- C++ -*-

// Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
// Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

//
// ISO C++ 14882: 21 Strings library
//

/** @file basic_string.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef _BASIC_STRING_H
#define _BASIC_STRING_H 1

#pragma GCC system_header

#include <bits/atomicity.h>
#include <debug/debug.h>

namespace std
{
  /**
   *  @class basic_string basic_string.h <string>
   *  @brief  Managing sequences of characters and character-like objects.
   *
   *  @ingroup Containers
   *  @ingroup Sequences
   *
   *  Meets the requirements of a <a href="tables.html#65">container</a>, a
   *  <a href="tables.html#66">reversible container</a>, and a
   *  <a href="tables.html#67">sequence</a>.  Of the
   *  <a href="tables.html#68">optional sequence requirements</a>, only
   *  @c push_back, @c at, and array access are supported.
   *
   *  @doctodo
   *
   *
   *  @if maint
   *  Documentation?  What's that?
   *  Nathan Myers <[e-mail]>.
   *
   *  A string looks like this:
   *
   *  @code
   *                                        [_Rep]
   *                                        _M_length
   *   [basic_string<char_type>]            _M_capacity
   *   _M_dataplus                          _M_refcount
   *   _M_p ---------------->               unnamed array of char_type
   *  @endcode
   *
   *  Where the _M_p points to the first character in the string, and
   *  you cast it to a pointer-to-_Rep and subtract 1 to get a
   *  pointer to the header.
   *
   *  This approach has the enormous advantage that a string object
   *  requires only one allocation.  All the ugliness is confined
   *  within a single pair of inline functions, which each compile to
   *  a single "add" instruction: _Rep::_M_data(), and
   *  string::_M_rep(); and the allocation function which gets a
   *  block of raw bytes and with room enough and constructs a _Rep
   *  object at the front.
   *
   *  The reason you want _M_data pointing to the character array and
   *  not the _Rep is so that the debugger can see the string
   *  contents. (Probably we should add a non-inline member to get
   *  the _Rep for the debugger to use, so users can check the actual
   *  string length.)
   *
   *  Note that the _Rep object is a POD so that you can have a
   *  static "empty string" _Rep object already "constructed" before
   *  static constructors have run.  The reference-count encoding is
   *  chosen so that a 0 indicates one reference, so you never try to
   *  destroy the empty-string _Rep object.
   *
   *  All but the last paragraph is considered pretty conventional
   *  for a C++ string implementation.
   *  @endif
  */
  // 21.3  Template class basic_string
  template<typename _CharT, typename _Traits, typename _Alloc>
    class basic_string
    {
      typedef typename _Alloc::template rebind<_CharT>::other _CharT_alloc_type;

      // Types:
    public:
      typedef _Traits					    traits_type;
      typedef typename _Traits::char_type		    value_type;
      typedef _Alloc					    allocator_type;
      typedef typename _CharT_alloc_type::size_type	    size_type;
      typedef typename _CharT_alloc_type::difference_type   difference_type;
      typedef typename _CharT_alloc_type::reference	    reference;
      typedef typename _CharT_alloc_type::const_reference   const_reference;
      typedef typename _CharT_alloc_type::pointer	    pointer;
      typedef typename _CharT_alloc_type::const_pointer	    const_pointer;
      typedef __gnu_cxx::__normal_iterator<pointer, basic_string>  iterator;
      typedef __gnu_cxx::__normal_iterator<const_pointer, basic_string>
                                                            const_iterator;
      typedef std::reverse_iterator<const_iterator>	const_reverse_iterator;
      typedef std::reverse_iterator<iterator>		    reverse_iterator;

    private:
      // _Rep: string representation
      //   Invariants:
      //   1. String really contains _M_length + 1 characters: due to 21.3.4
      //      must be kept null-terminated.
      //   2. _M_capacity >= _M_length
      //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
      //   3. _M_refcount has three states:
      //      -1: leaked, one reference, no ref-copies allowed, non-const.
      //       0: one reference, non-const.
      //     n>0: n + 1 references, operations require a lock, const.
      //   4. All fields==0 is an empty string, given the extra storage
      //      beyond-the-end for a null terminator; thus, the shared
      //      empty string representation needs no constructor.

      struct _Rep_base
      {
	size_type		_M_length;
	size_type		_M_capacity;
	_Atomic_word		_M_refcount;
      };

      struct _Rep : _Rep_base
      {
	// Types:
	typedef typename _Alloc::template rebind<char>::other _Raw_bytes_alloc;

	// (Public) Data members:

	// The maximum number of individual char_type elements of an
	// individual string is determined by _S_max_size. This is the
	// value that will be returned by max_size().  (Whereas npos
	// is the maximum number of bytes the allocator can allocate.)
	// If one was to divvy up the theoretical largest size string,
	// with a terminating character and m _CharT elements, it'd
	// look like this:
	// npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
	// Solving for m:
	// m = ((npos - sizeof(_Rep))/sizeof(CharT)) - 1
	// In addition, this implementation quarters this amount.
	static const size_type	_S_max_size;
	static const _CharT	_S_terminal;

	// The following storage is init'd to 0 by the linker, resulting
        // (carefully) in an empty string with one reference.
        static size_type _S_empty_rep_storage[];

        static _Rep&
        _S_empty_rep()
        {
	  void* __p = reinterpret_cast<void*>(&_S_empty_rep_storage);
	  return *reinterpret_cast<_Rep*>(__p);
	}

        bool
	_M_is_leaked() const
        { return this->_M_refcount < 0; }

        bool
	_M_is_shared() const
        { return this->_M_refcount > 0; }

        void
	_M_set_leaked()
        { this->_M_refcount = -1; }

        void
	_M_set_sharable()
        { this->_M_refcount = 0; }

	void
	_M_set_length_and_sharable(size_type __n)
	{ 
	  this->_M_set_sharable();  // One reference.
	  this->_M_length = __n;
	  traits_type::assign(this->_M_refdata()[__n], _S_terminal);
	  // grrr. (per 21.3.4)
	  // You cannot leave those LWG people alone for a second.
	}

	_CharT*
	_M_refdata() throw()
	{ return reinterpret_cast<_CharT*>(this + 1); }

	_CharT*
	_M_grab(const _Alloc& __alloc1, const _Alloc& __alloc2)
	{
	  return (!_M_is_leaked() && __alloc1 == __alloc2)
	          ? _M_refcopy() : _M_clone(__alloc1);
	}

	// Create & Destroy
	static _Rep*
	_S_create(size_type, size_type, const _Alloc&);

	void
	_M_dispose(const _Alloc& __a)
	{
#ifndef _GLIBCXX_FULLY_DYNAMIC_STRING
	  if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
	    if (__gnu_cxx::__exchange_and_add(&this->_M_refcount, -1) <= 0)
	      _M_destroy(__a);
	}  // XXX MT

	void
	_M_destroy(const _Alloc&) throw();

	_CharT*
	_M_refcopy() throw()
	{
#ifndef _GLIBCXX_FULLY_DYNAMIC_STRING
	  if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
            __gnu_cxx::__atomic_add(&this->_M_refcount, 1);
	  return _M_refdata();
	}  // XXX MT

	_CharT*
	_M_clone(const _Alloc&, size_type __res = 0);
      };

      // Use empty-base optimization: http://www.cantrip.org/emptyopt.html
      struct _Alloc_hider : _Alloc
      {
	_Alloc_hider(_CharT* __dat, const _Alloc& __a)
	: _Alloc(__a), _M_p(__dat) { }

	_CharT* _M_p; // The actual data.
      };

    public:
      // Data Members (public):
      // NB: This is an unsigned type, and thus represents the maximum
      // size that the allocator can hold.
      ///  Value returned by various member functions when they fail.
      static const size_type	npos = static_cast<size_type>(-1);

    private:
      // Data Members (private):
      mutable _Alloc_hider	_M_dataplus;

      _CharT*
      _M_data() const
      { return  _M_dataplus._M_p; }

      _CharT*
      _M_data(_CharT* __p)
      { return (_M_dataplus._M_p = __p); }

      _Rep*
      _M_rep() const
      { return &((reinterpret_cast<_Rep*> (_M_data()))[-1]); }

      // For the internal use we have functions similar to `begin'/`end'
      // but they do not call _M_leak.
      iterator
      _M_ibegin() const
      { return iterator(_M_data()); }

      iterator
      _M_iend() const
      { return iterator(_M_data() + this->size()); }

      void
      _M_leak()    // for use in begin() & non-const op[]
      {
	if (!_M_rep()->_M_is_leaked())
	  _M_leak_hard();
      }

      size_type
      _M_check(size_type __pos, const char* __s) const
      {
	if (__pos > this->size())
	  __throw_out_of_range(__N(__s));
	return __pos;
      }

      void
      _M_check_length(size_type __n1, size_type __n2, const char* __s) const
      {
	if (this->max_size() - (this->size() - __n1) < __n2)
	  __throw_length_error(__N(__s));
      }

      // NB: _M_limit doesn't check for a bad __pos value.
      size_type
      _M_limit(size_type __pos, size_type __off) const
      {
	const bool __testoff =  __off < this->size() - __pos;
	return __testoff ? __off : this->size() - __pos;
      }

      // True if _Rep and source do not overlap.
      bool
      _M_disjunct(const _CharT* __s) const
      {
	return (less<const _CharT*>()(__s, _M_data())
		|| less<const _CharT*>()(_M_data() + this->size(), __s));
      }

      // When __n = 1 way faster than the general multichar
      // traits_type::copy/move/assign.
      static void
      _M_copy(_CharT* __d, const _CharT* __s, size_type __n)
      {
	if (__n == 1)
	  traits_type::assign(*__d, *__s);
	else
	  traits_type::copy(__d, __s, __n);
      }

      static void
      _M_move(_CharT* __d, const _CharT* __s, size_type __n)
      {
	if (__n == 1)
	  traits_type::assign(*__d, *__s);
	else
	  traits_type::move(__d, __s, __n);	  
      }

      static void
      _M_assign(_CharT* __d, size_type __n, _CharT __c)
      {
	if (__n == 1)
	  traits_type::assign(*__d, __c);