bitset

// <bitset> -*- C++ -*-

// Copyright (C) 2001, 2002, 2003, 2004 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, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// 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.

/*
 * Copyright (c) 1998
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file bitset
 *  This is a Standard C++ Library header.  You should @c #include this header
 *  in your programs, rather than any of the "st[dl]_*.h" implementation files.
 */

#ifndef _GLIBCXX_BITSET
#define _GLIBCXX_BITSET 1

#pragma GCC system_header

#include <cstddef>     // For size_t
#include <cstring>     // For memset
#include <limits>      // For numeric_limits
#include <string>
#include <bits/functexcept.h>   // For invalid_argument, out_of_range,
                                // overflow_error
#include <ostream>     // For ostream (operator<<)
#include <istream>     // For istream (operator>>)

#define _GLIBCXX_BITSET_BITS_PER_WORD  numeric_limits<unsigned long>::digits
#define _GLIBCXX_BITSET_WORDS(__n) \
 ((__n) < 1 ? 0 : ((__n) + _GLIBCXX_BITSET_BITS_PER_WORD - 1)/_GLIBCXX_BITSET_BITS_PER_WORD)

namespace _GLIBCXX_STD
{
  /**
   *  @if maint
   *  Base class, general case.  It is a class inveriant that _Nw will be
   *  nonnegative.
   *
   *  See documentation for bitset.
   *  @endif
  */
  template<size_t _Nw>
    struct _Base_bitset
    {
      typedef unsigned long _WordT;

      /// 0 is the least significant word.
      _WordT        _M_w[_Nw];

      _Base_bitset() { _M_do_reset(); }
      _Base_bitset(unsigned long __val)
      {
    _M_do_reset();
    _M_w[0] = __val;
      }

      static size_t
      _S_whichword(size_t __pos )
      { return __pos / _GLIBCXX_BITSET_BITS_PER_WORD; }

      static size_t
      _S_whichbyte(size_t __pos )
      { return (__pos % _GLIBCXX_BITSET_BITS_PER_WORD) / __CHAR_BIT__; }

      static size_t
      _S_whichbit(size_t __pos )
      { return __pos % _GLIBCXX_BITSET_BITS_PER_WORD; }

      static _WordT
      _S_maskbit(size_t __pos )
      { return (static_cast<_WordT>(1)) << _S_whichbit(__pos); }

      _WordT&
      _M_getword(size_t __pos)
      { return _M_w[_S_whichword(__pos)]; }

      _WordT
      _M_getword(size_t __pos) const
      { return _M_w[_S_whichword(__pos)]; }

      _WordT&
      _M_hiword() { return _M_w[_Nw - 1]; }

      _WordT
      _M_hiword() const { return _M_w[_Nw - 1]; }

      void
      _M_do_and(const _Base_bitset<_Nw>& __x)
      {
    for (size_t __i = 0; __i < _Nw; __i++)
      _M_w[__i] &= __x._M_w[__i];
      }

      void
      _M_do_or(const _Base_bitset<_Nw>& __x)
      {
    for (size_t __i = 0; __i < _Nw; __i++)
      _M_w[__i] |= __x._M_w[__i];
      }

      void
      _M_do_xor(const _Base_bitset<_Nw>& __x)
      {
    for (size_t __i = 0; __i < _Nw; __i++)
      _M_w[__i] ^= __x._M_w[__i];
      }

      void
      _M_do_left_shift(size_t __shift);

      void
      _M_do_right_shift(size_t __shift);

      void
      _M_do_flip()
      {
    for (size_t __i = 0; __i < _Nw; __i++)
      _M_w[__i] = ~_M_w[__i];
      }

      void
      _M_do_set()
      {
    for (size_t __i = 0; __i < _Nw; __i++)
      _M_w[__i] = ~static_cast<_WordT>(0);
      }

      void
      _M_do_reset() { memset(_M_w, 0, _Nw * sizeof(_WordT)); }

      bool
      _M_is_equal(const _Base_bitset<_Nw>& __x) const
      {
    for (size_t __i = 0; __i < _Nw; ++__i)
      {
        if (_M_w[__i] != __x._M_w[__i])
          return false;
      }
    return true;
      }

      bool
      _M_is_any() const
      {
    for (size_t __i = 0; __i < _Nw; __i++)
      {
        if (_M_w[__i] != static_cast<_WordT>(0))
          return true;
      }
    return false;
      }

      size_t
      _M_do_count() const
      {
    size_t __result = 0;
    for (size_t __i = 0; __i < _Nw; __i++)
      __result += __builtin_popcountl(_M_w[__i]);
    return __result;
      }

      unsigned long
      _M_do_to_ulong() const;

      // find first "on" bit
      size_t
      _M_do_find_first(size_t __not_found) const;

      // find the next "on" bit that follows "prev"
      size_t
      _M_do_find_next(size_t __prev, size_t __not_found) const;
    };

  // Definitions of non-inline functions from _Base_bitset.
  template<size_t _Nw>
    void
    _Base_bitset<_Nw>::_M_do_left_shift(size_t __shift)
    {
      if (__builtin_expect(__shift != 0, 1))
    {
      const size_t __wshift = __shift / _GLIBCXX_BITSET_BITS_PER_WORD;
      const size_t __offset = __shift % _GLIBCXX_BITSET_BITS_PER_WORD;

      if (__offset == 0)
        for (size_t __n = _Nw - 1; __n >= __wshift; --__n)
          _M_w[__n] = _M_w[__n - __wshift];
      else
        {
          const size_t __sub_offset = _GLIBCXX_BITSET_BITS_PER_WORD - __offset;
          for (size_t __n = _Nw - 1; __n > __wshift; --__n)
        _M_w[__n] = (_M_w[__n - __wshift] << __offset) |
          (_M_w[__n - __wshift - 1] >> __sub_offset);
          _M_w[__wshift] = _M_w[0] << __offset;
        }

      std::fill(_M_w + 0, _M_w + __wshift, static_cast<_WordT>(0));
    }
    }

  template<size_t _Nw>
    void
    _Base_bitset<_Nw>::_M_do_right_shift(size_t __shift)
    {
      if (__builtin_expect(__shift != 0, 1))
    {
      const size_t __wshift = __shift / _GLIBCXX_BITSET_BITS_PER_WORD;
      const size_t __offset = __shift % _GLIBCXX_BITSET_BITS_PER_WORD;
      const size_t __limit = _Nw - __wshift - 1;

      if (__offset == 0)
        for (size_t __n = 0; __n <= __limit; ++__n)
          _M_w[__n] = _M_w[__n + __wshift];
      else
        {
          const size_t __sub_offset = _GLIBCXX_BITSET_BITS_PER_WORD - __offset;
          for (size_t __n = 0; __n < __limit; ++__n)
        _M_w[__n] = (_M_w[__n + __wshift] >> __offset) |
          (_M_w[__n + __wshift + 1] << __sub_offset);
          _M_w[__limit] = _M_w[_Nw-1] >> __offset;
        }
      
      std::fill(_M_w + __limit + 1, _M_w + _Nw, static_cast<_WordT>(0));
    }
    }

  template<size_t _Nw>
    unsigned long
    _Base_bitset<_Nw>::_M_do_to_ulong() const
    {
      for (size_t __i = 1; __i < _Nw; ++__i)
    if (_M_w[__i])
      __throw_overflow_error(__N("_Base_bitset::_M_do_to_ulong"));
      return _M_w[0];
    }

  template<size_t _Nw>
    size_t
    _Base_bitset<_Nw>::_M_do_find_first(size_t __not_found) const
    {
      for (size_t __i = 0; __i < _Nw; __i++)
    {
      _WordT __thisword = _M_w[__i];
      if (__thisword != static_cast<_WordT>(0))
        return __i * _GLIBCXX_BITSET_BITS_PER_WORD
          + __builtin_ctzl(__thisword);
    }
      // not found, so return an indication of failure.
      return __not_found;
    }

  template<size_t _Nw>
    size_t
    _Base_bitset<_Nw>::_M_do_find_next(size_t __prev, size_t __not_found) const
    {
      // make bound inclusive
      ++__prev;

      // check out of bounds
      if (__prev >= _Nw * _GLIBCXX_BITSET_BITS_PER_WORD)
    return __not_found;

      // search first word
      size_t __i = _S_whichword(__prev);
      _WordT __thisword = _M_w[__i];

      // mask off bits below bound
      __thisword &= (~static_cast<_WordT>(0)) << _S_whichbit(__prev);

      if (__thisword != static_cast<_WordT>(0))
    return __i * _GLIBCXX_BITSET_BITS_PER_WORD
      + __builtin_ctzl(__thisword);

      // check subsequent words
      __i++;
      for ( ; __i < _Nw; __i++ )
    {
      __thisword = _M_w[__i];
      if (__thisword != static_cast<_WordT>(0))
        return __i * _GLIBCXX_BITSET_BITS_PER_WORD
          + __builtin_ctzl(__thisword);
    }
      // not found, so return an indication of failure.
      return __not_found;
    } // end _M_do_find_next


  /**
   *  @if maint
   *  Base class, specialization for a single word.
   *
   *  See documentation for bitset.
   *  @endif
  */
  template<>
    struct _Base_bitset<1>
    {
      typedef unsigned long _WordT;
      _WordT _M_w;

      _Base_bitset( void ) : _M_w(0) {}
      _Base_bitset(unsigned long __val) : _M_w(__val) {}

      static size_t
      _S_whichword(size_t __pos )
      { return __pos / _GLIBCXX_BITSET_BITS_PER_WORD; }

      static size_t
      _S_whichbyte(size_t __pos )
      { return (__pos % _GLIBCXX_BITSET_BITS_PER_WORD) / __CHAR_BIT__; }

      static size_t
      _S_whichbit(size_t __pos )
      {  return __pos % _GLIBCXX_BITSET_BITS_PER_WORD; }

      static _WordT
      _S_maskbit(size_t __pos )
      { return (static_cast<_WordT>(1)) << _S_whichbit(__pos); }

      _WordT&
      _M_getword(size_t) { return _M_w; }

      _WordT
      _M_getword(size_t) const { return _M_w; }

      _WordT&
      _M_hiword() { return _M_w; }

      _WordT
      _M_hiword() const { return _M_w; }

      void
      _M_do_and(const _Base_bitset<1>& __x) { _M_w &= __x._M_w; }

      void
      _M_do_or(const _Base_bitset<1>& __x)  { _M_w |= __x._M_w; }

      void
      _M_do_xor(const _Base_bitset<1>& __x) { _M_w ^= __x._M_w; }

      void
      _M_do_left_shift(size_t __shift) { _M_w <<= __shift; }

      void
      _M_do_right_shift(size_t __shift) { _M_w >>= __shift; }

      void
      _M_do_flip() { _M_w = ~_M_w; }

      void
      _M_do_set() { _M_w = ~static_cast<_WordT>(0); }

      void
      _M_do_reset() { _M_w = 0; }

      bool
      _M_is_equal(const _Base_bitset<1>& __x) const
      { return _M_w == __x._M_w; }

      bool
      _M_is_any() const { return _M_w != 0; }

      size_t
      _M_do_count() const { return __builtin_popcountl(_M_w); }

      unsigned long
      _M_do_to_ulong() const { return _M_w; }

      size_t
      _M_do_find_first(size_t __not_found) const
      {
        if (_M_w != 0)
          return __builtin_ctzl(_M_w);
        else
          return __not_found;
      }

      // find the next "on" bit that follows "prev"
      size_t
      _M_do_find_next(size_t __prev, size_t __not_found) const
      {
    ++__prev;
    if (__prev >= ((size_t) _GLIBCXX_BITSET_BITS_PER_WORD))
      return __not_found;

    _WordT __x = _M_w >> __prev;
    if (__x != 0)
      return __builtin_ctzl(__x) + __prev;
    else
      return __not_found;
      }
    };


  /**
   *  @if maint
   *  Base class, specialization for no storage (zero-length %bitset).
   *
   *  See documentation for bitset.
   *  @endif
  */
  template<>
    struct _Base_bitset<0>
    {
      typedef unsigned long _WordT;

      _Base_bitset() {}
      _Base_bitset(unsigned long) {}

      static size_t
      _S_whichword(size_t __pos )
      { return __pos / _GLIBCXX_BITSET_BITS_PER_WORD; }

      static size_t
      _S_whichbyte(size_t __pos )
      { return (__pos % _GLIBCXX_BITSET_BITS_PER_WORD) / __CHAR_BIT__; }

      static size_t
      _S_whichbit(size_t __pos )
      {  return __pos % _GLIBCXX_BITSET_BITS_PER_WORD; }

      static _WordT
      _S_maskbit(size_t __pos )
      { return (static_cast<_WordT>(1)) << _S_whichbit(__pos); }

      // This would normally give access to the data.  The bounds-checking
      // in the bitset class will prevent the user from getting this far,
      // but (1) it must still return an lvalue to compile, and (2) the
      // user might call _Unchecked_set directly, in which case this /needs/
      // to fail.  Let's not penalize zero-length users unless they actually
      // make an unchecked call; all the memory ugliness is therefore
      // localized to this single should-never-get-this-far function.
      _WordT&
      _M_getword(size_t) const
      { 
    __throw_out_of_range(__N("_Base_bitset::_M_getword")); 
    return *new _WordT; 
      }

      _WordT
      _M_hiword() const { return 0; }

      void
      _M_do_and(const _Base_bitset<0>&) { }

      void
      _M_do_or(const _Base_bitset<0>&)  { }

      void
      _M_do_xor(const _Base_bitset<0>&) { }

      void
      _M_do_left_shift(size_t) { }

      void
      _M_do_right_shift(size_t) { }

      void
      _M_do_flip() { }

      void
      _M_do_set() { }

      void
      _M_do_reset() { }

      // Are all empty bitsets equal to each other?  Are they equal to
      // themselves?  How to compare a thing which has no state?  What is
      // the sound of one zero-length bitset clapping?
      bool
      _M_is_equal(const _Base_bitset<0>&) const { return true; }

      bool
      _M_is_any() const { return false; }

      size_t
      _M_do_count() const { return 0; }

      unsigned long
      _M_do_to_ulong() const { return 0; }

      // Normally "not found" is the size, but that could also be
      // misinterpreted as an index in this corner case.  Oh well.
      size_t
      _M_do_find_first(size_t) const { return 0; }

      size_t
      _M_do_find_next(size_t, size_t) const { return 0; }
    };


  // Helper class to zero out the unused high-order bits in the highest word.
  template<size_t _Extrabits>
    struct _Sanitize
    {
      static void _S_do_sanitize(unsigned long& __val)
      { __val &= ~((~static_cast<unsigned long>(0)) << _Extrabits); }
    };

  template<>
    struct _Sanitize<0>
    { static void _S_do_sanitize(unsigned long) { } };


  /**
   *  @brief  The %bitset class represents a @e fixed-size sequence of bits.
   *
   *  @ingroup Containers
   *
   *  (Note that %bitset does @e not meet the formal requirements of a
   *  <a href="tables.html#65">container</a>.  Mainly, it lacks iterators.)
   *
   *  The template argument, @a Nb, may be any non-negative number,
   *  specifying the number of bits (e.g., "0", "12", "1024*1024").
   *
   *  In the general unoptimized case, storage is allocated in word-sized
   *  blocks.  Let B be the number of bits in a word, then (Nb+(B-1))/B
   *  words will be used for storage.  B - Nb%B bits are unused.  (They are
   *  the high-order bits in the highest word.)  It is a class invariant
   *  that those unused bits are always zero.
   *
   *  If you think of %bitset as "a simple array of bits," be aware that
   *  your mental picture is reversed:  a %bitset behaves the same way as
   *  bits in integers do, with the bit at index 0 in the "least significant
   *  / right-hand" position, and the bit at index Nb-1 in the "most
   *  significant / left-hand" position.  Thus, unlike other containers, a
   *  %bitset's index "counts from right to left," to put it very loosely.
   *
   *  This behavior is preserved when translating to and from strings.  For
   *  example, the first line of the following program probably prints
   *  "b('a') is 0001100001" on a modern ASCII system.
   *
   *  @code
   *     #include <bitset>
   *     #include <iostream>
   *     #include <sstream>
   *
   *     using namespace std;
   *
   *     int main()
   *     {
   *         long         a = 'a';
   *         bitset<10>   b(a);
   *
   *         cout << "b('a') is " << b << endl;
   *
   *         ostringstream s;
   *         s << b;
   *         string  str = s.str();
   *         cout << "index 3 in the string is " << str[3] << " but\n"
   *              << "index 3 in the bitset is " << b[3] << endl;
   *     }
   *  @endcode
   *
   *  Also see http://gcc.gnu.org/onlinedocs/libstdc++/ext/sgiexts.html#ch23
   *  for a description of extensions.
   *
   *  @if maint
   *  Most of the actual code isn't contained in %bitset<> itself, but in the
   *  base class _Base_bitset.  The base class works with whole words, not with
   *  individual bits.  This allows us to specialize _Base_bitset for the
   *  important special case where the %bitset is only a single word.
   *
   *  Extra confusion can result due to the fact that the storage for
   *  _Base_bitset @e is a regular array, and is indexed as such.  This is
   *  carefully encapsulated.
   *  @endif
  */
  template<size_t _Nb>
    class bitset : private _Base_bitset<_GLIBCXX_BITSET_WORDS(_Nb)>
  {
  private:
    typedef _Base_bitset<_GLIBCXX_BITSET_WORDS(_Nb)> _Base;
    typedef unsigned long _WordT;

    void
    _M_do_sanitize()
    {
      _Sanitize<_Nb%_GLIBCXX_BITSET_BITS_PER_WORD>::
          _S_do_sanitize(this->_M_hiword());
    }

  public:
    /**
     *  This encapsulates the concept of a single bit.  An instance of this
     *  class is a proxy for an actual bit; this way the individual bit
     *  operations are done as faster word-size bitwise instructions.
     *
     *  Most users will never need to use this class directly; conversions
     *  to and from bool are automatic and should be transparent.  Overloaded
     *  operators help to preserve the illusion.
     *
     *  (On a typical system, this "bit %reference" is 64 times the size of
     *  an actual bit.  Ha.)
    */
    class reference
    {
      friend class bitset;

      _WordT *_M_wp;
      size_t _M_bpos;

      // left undefined
      reference();

    public:
      reference(bitset& __b, size_t __pos)
      {
    _M_wp = &__b._M_getword(__pos);
    _M_bpos = _Base::_S_whichbit(__pos);
      }

      ~reference() { }

      // For b[i] = __x;
      reference&
      operator=(bool __x)
      {
    if ( __x )
      *_M_wp |= _Base::_S_maskbit(_M_bpos);
    else
      *_M_wp &= ~_Base::_S_maskbit(_M_bpos);
    return *this;
      }

      // For b[i] = b[__j];
      reference&
      operator=(const reference& __j)
      {
    if ( (*(__j._M_wp) & _Base::_S_maskbit(__j._M_bpos)) )
      *_M_wp |= _Base::_S_maskbit(_M_bpos);
    else
      *_M_wp &= ~_Base::_S_maskbit(_M_bpos);
    return *this;
      }

      // Flips the bit
      bool
      operator~() const
      { return (*(_M_wp) & _Base::_S_maskbit(_M_bpos)) == 0; }

      // For __x = b[i];
      operator bool() const
      { return (*(_M_wp) & _Base::_S_maskbit(_M_bpos)) != 0; }

      // For b[i].flip();
      reference&
      flip()
      {
    *_M_wp ^= _Base::_S_maskbit(_M_bpos);
    return *this;
      }
    };
    friend class reference;

    // 23.3.5.1 constructors:
    /// All bits set to zero.
    bitset() { }

    /// Initial bits bitwise-copied from a single word (others set to zero).
    bitset(unsigned long __val) : _Base(__val)
    { _M_do_sanitize(); }

    /**
     *  @brief  Use a subset of a string.
     *  @param  s  A string of '0' and '1' characters.
     *  @param  position  Index of the first character in @a s to use; defaults
     *               to zero.
     *  @throw  std::out_of_range  If @a pos is bigger the size of @a s.
     *  @throw  std::invalid_argument  If a character appears in the string
     *                                 which is neither '0' nor '1'.
    */
    template<class _CharT, class _Traits, class _Alloc>
      explicit bitset(const basic_string<_CharT, _Traits, _Alloc>& __s,
              size_t __position = 0) : _Base()
      {
    if (__position > __s.size())
      __throw_out_of_range(__N("bitset::bitset initial position "
                   "not valid"));
    _M_copy_from_string(__s, __position,
                basic_string<_CharT, _Traits, _Alloc>::npos);
      }

    /**
     *  @brief  Use a subset of a string.
     *  @param  s  A string of '0' and '1' characters.
     *  @param  position  Index of the first character in @a s to use.
     *  @param  n    The number of characters to copy.
     *  @throw  std::out_of_range  If @a pos is bigger the size of @a s.
     *  @throw  std::invalid_argument  If a character appears in the string
     *                                 which is neither '0' nor '1'.
    */
    template<class _CharT, class _Traits, class _Alloc>
      bitset(const basic_string<_CharT, _Traits, _Alloc>& __s,
         size_t __position, size_t __n) : _Base()
      {
    if (__position > __s.size())
     __throw_out_of_range(__N("bitset::bitset initial position "
                  "not valid"));
    _M_copy_from_string(__s, __position, __n);
      }

    // 23.3.5.2 bitset operations:
    //@{
    /**
     *  @brief  Operations on bitsets.
     *  @param  rhs  A same-sized bitset.
     *
     *  These should be self-explanatory.
    */
    bitset<_Nb>&
    operator&=(const bitset<_Nb>& __rhs)
    {
      this->_M_do_and(__rhs);
      return *this;
    }

    bitset<_Nb>&
    operator|=(const bitset<_Nb>& __rhs)
    {
      this->_M_do_or(__rhs);
      return *this;
    }

    bitset<_Nb>&
    operator^=(const bitset<_Nb>& __rhs)
    {
      this->_M_do_xor(__rhs);
      return *this;
    }
    //@}

    //@{
    /**
     *  @brief  Operations on bitsets.
     *  @param  position  The number of places to shift.
     *
     *  These should be self-explanatory.
    */
    bitset<_Nb>&
    operator<<=(size_t __position)
    {
      if (__builtin_expect(__position < _Nb, 1))
        {
          this->_M_do_left_shift(__position);
          this->_M_do_sanitize();
        }
      else
    this->_M_do_reset();
      return *this;
    }

    bitset<_Nb>&
    operator>>=(size_t __position)
    {
      if (__builtin_expect(__position < _Nb, 1))
        {
          this->_M_do_right_shift(__position);
          this->_M_do_sanitize();
        }
      else
    this->_M_do_reset();
      return *this;
    }
    //@}

    //@{
    /**
     *  These versions of single-bit set, reset, flip, and test are
     *  extensions from the SGI version.  They do no range checking.
     *  @ingroup SGIextensions
    */
    bitset<_Nb>&
    _Unchecked_set(size_t __pos)
    {
      this->_M_getword(__pos) |= _Base::_S_maskbit(__pos);
      return *this;
    }

    bitset<_Nb>&
    _Unchecked_set(size_t __pos, int __val)
    {
      if (__val)
    this->_M_getword(__pos) |= _Base::_S_maskbit(__pos);
      else
    this->_M_getword(__pos) &= ~_Base::_S_maskbit(__pos);
      return *this;
    }

    bitset<_Nb>&
    _Unchecked_reset(size_t __pos)
    {
      this->_M_getword(__pos) &= ~_Base::_S_maskbit(__pos);
      return *this;
    }

    bitset<_Nb>&
    _Unchecked_flip(size_t __pos)
    {
      this->_M_getword(__pos) ^= _Base::_S_maskbit(__pos);
      return *this;
    }

    bool
    _Unchecked_test(size_t __pos) const
    {
      return (this->_M_getword(__pos) & _Base::_S_maskbit(__pos))
    != static_cast<_WordT>(0);
    }
    //@}

    // Set, reset, and flip.
    /**
     *  @brief Sets every bit to true.
    */
    bitset<_Nb>&
    set()
    {
      this->_M_do_set();
      this->_M_do_sanitize();
      return *this;
    }

    /**
     *  @brief Sets a given bit to a particular value.
     *  @param  position  The index of the bit.
     *  @param  val  Either true or false, defaults to true.
     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
    */
    bitset<_Nb>&
    set(size_t __position, bool __val = true)
    {
      if (__position >= _Nb)
    __throw_out_of_range(__N("bitset::set"));
      return _Unchecked_set(__position, __val);
    }

    /**
     *  @brief Sets every bit to false.
    */
    bitset<_Nb>&
    reset()
    {
      this->_M_do_reset();
      return *this;
    }

    /**
     *  @brief Sets a given bit to false.
     *  @param  position  The index of the bit.
     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
     *
     *  Same as writing @c set(pos,false).
    */
    bitset<_Nb>&
    reset(size_t __position)
    {
      if (__position >= _Nb)
    __throw_out_of_range(__N("bitset::reset"));
      return _Unchecked_reset(__position);
    }

    /**
     *  @brief Toggles every bit to its opposite value.
    */
    bitset<_Nb>&
    flip()
    {
      this->_M_do_flip();
      this->_M_do_sanitize();
      return *this;
    }

    /**
     *  @brief Toggles a given bit to its opposite value.
     *  @param  position  The index of the bit.
     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
    */
    bitset<_Nb>&
    flip(size_t __position)
    {
      if (__position >= _Nb)
    __throw_out_of_range(__N("bitset::flip"));
      return _Unchecked_flip(__position);
    }

    /// See the no-argument flip().
    bitset<_Nb>
    operator~() const { return bitset<_Nb>(*this).flip(); }

    //@{
    /**
     *  @brief  Array-indexing support.
     *  @param  position  Index into the %bitset.
     *  @return  A bool for a 'const %bitset'.  For non-const bitsets, an
     *           instance of the reference proxy class.
     *  @note  These operators do no range checking and throw no exceptions,
     *         as required by DR 11 to the standard.
     *
     *  @if maint
     *  _GLIBCXX_RESOLVE_LIB_DEFECTS Note that this implementation already
     *  resolves DR 11 (items 1 and 2), but does not do the range-checking
     *  required by that DR's resolution.  -pme
     *  The DR has since been changed:  range-checking is a precondition
     *  (users' responsibility), and these functions must not throw.  -pme
     *  @endif
    */
    reference
    operator[](size_t __position) { return reference(*this,__position); }

    bool
    operator[](size_t __position) const { return _Unchecked_test(__position); }
    //@}

    /**
     *  @brief Retuns a numerical interpretation of the %bitset.
     *  @return  The integral equivalent of the bits.
     *  @throw  std::overflow_error  If there are too many bits to be
     *                               represented in an @c unsigned @c long.
    */
    unsigned long
    to_ulong() const { return this->_M_do_to_ulong(); }

    /**
     *  @brief Retuns a character interpretation of the %bitset.
     *  @return  The string equivalent of the bits.
     *
     *  Note the ordering of the bits:  decreasing character positions
     *  correspond to increasing bit positions (see the main class notes for
     *  an example).
     *
     *  Also note that you must specify the string's template parameters
     *  explicitly.  Given a bitset @c bs and a string @s:
     *  @code
     *     s = bs.to_string<char,char_traits<char>,allocator<char> >();
     *  @endcode
    */
    template<class _CharT, class _Traits, class _Alloc>
      basic_string<_CharT, _Traits, _Alloc>
      to_string() const
      {
    basic_string<_CharT, _Traits, _Alloc> __result;
    _M_copy_to_string(__result);
    return __result;
      }

    // Helper functions for string operations.
    template<class _CharT, class _Traits, class _Alloc>
      void
      _M_copy_from_string(const basic_string<_CharT,_Traits,_Alloc>& __s,
                          size_t, size_t);

    template<class _CharT, class _Traits, class _Alloc>
      void
      _M_copy_to_string(basic_string<_CharT,_Traits,_Alloc>&) const;

    /// Returns the number of bits which are set.
    size_t
    count() const { return this->_M_do_count(); }

    /// Returns the total number of bits.
    size_t
    size() const { return _Nb; }

    //@{
    /// These comparisons for equality/inequality are, well, @e bitwise.
    bool
    operator==(const bitset<_Nb>& __rhs) const
    { return this->_M_is_equal(__rhs); }

    bool
    operator!=(const bitset<_Nb>& __rhs) const
    { return !this->_M_is_equal(__rhs); }
    //@}

    /**
     *  @brief Tests the value of a bit.
     *  @param  position  The index of a bit.
     *  @return  The value at @a pos.
     *  @throw  std::out_of_range  If @a pos is bigger the size of the %set.
    */
    bool
    test(size_t __position) const
    {
      if (__position >= _Nb)
    __throw_out_of_range(__N("bitset::test"));
      return _Unchecked_test(__position);
    }

    /**
     *  @brief Tests whether any of the bits are on.
     *  @return  True if at least one bit is set.
    */
    bool
    any() const { return this->_M_is_any(); }

    /**
     *  @brief Tests whether any of the bits are on.
     *  @return  True if none of the bits are set.
    */
    bool
    none() const { return !this->_M_is_any(); }

    //@{
    /// Self-explanatory.
    bitset<_Nb>
    operator<<(size_t __position) const
    { return bitset<_Nb>(*this) <<= __position; }

    bitset<_Nb>
    operator>>(size_t __position) const
    { return bitset<_Nb>(*this) >>= __position; }
    //@}

    /**
     *  @brief  Finds the index of the first "on" bit.
     *  @return  The index of the first bit set, or size() if not found.
     *  @ingroup SGIextensions
     *  @sa  _Find_next
    */
    size_t
    _Find_first() const
    { return this->_M_do_find_first(_Nb); }

    /**
     *  @brief  Finds the index of the next "on" bit after prev.
     *  @return  The index of the next bit set, or size() if not found.
     *  @param  prev  Where to start searching.
     *  @ingroup SGIextensions
     *  @sa  _Find_first
    */
    size_t
    _Find_next(size_t __prev ) const
    { return this->_M_do_find_next(__prev, _Nb); }
  };

  // Definitions of non-inline member functions.
  template<size_t _Nb>
    template<class _CharT, class _Traits, class _Alloc>
    void
    bitset<_Nb>::_M_copy_from_string(const basic_string<_CharT, _Traits,
                     _Alloc>& __s, size_t __pos, size_t __n)
    {
      reset();
      const size_t __nbits = std::min(_Nb, std::min(__n, __s.size() - __pos));
      for (size_t __i = 0; __i < __nbits; ++__i)
    {
      switch(__s[__pos + __nbits - __i - 1])
        {
        case '0':
          break;
        case '1':
          set(__i);
          break;
        default:
          __throw_invalid_argument(__N("bitset::_M_copy_from_string"));
        }
    }
    }

  template<size_t _Nb>
    template<class _CharT, class _Traits, class _Alloc>
    void
    bitset<_Nb>::_M_copy_to_string(basic_string<_CharT, _Traits,
                   _Alloc>& __s) const
    {
      __s.assign(_Nb, '0');
      for (size_t __i = 0; __i < _Nb; ++__i)
    if (_Unchecked_test(__i))
      __s[_Nb - 1 - __i] = '1';
    }

  // 23.3.5.3 bitset operations:
  //@{
  /**
   *  @brief  Global bitwise operations on bitsets.
   *  @param  x  A bitset.
   *  @param  y  A bitset of the same size as @a x.
   *  @return  A new bitset.
   *
   *  These should be self-explanatory.
  */
  template<size_t _Nb>
    inline bitset<_Nb>
    operator&(const bitset<_Nb>& __x, const bitset<_Nb>& __y)
    {
      bitset<_Nb> __result(__x);
      __result &= __y;
      return __result;
    }

  template<size_t _Nb>
    inline bitset<_Nb>
    operator|(const bitset<_Nb>& __x, const bitset<_Nb>& __y)
    {
      bitset<_Nb> __result(__x);
      __result |= __y;
      return __result;
    }

  template <size_t _Nb>
    inline bitset<_Nb>
    operator^(const bitset<_Nb>& __x, const bitset<_Nb>& __y)
    {
      bitset<_Nb> __result(__x);
      __result ^= __y;
      return __result;
    }
  //@}

  //@{
  /**
   *  @brief Global I/O operators for bitsets.
   *
   *  Direct I/O between streams and bitsets is supported.  Output is
   *  straightforward.  Input will skip whitespace, only accept '0' and '1'
   *  characters, and will only extract as many digits as the %bitset will
   *  hold.
  */
  template<class _CharT, class _Traits, size_t _Nb>
    basic_istream<_CharT, _Traits>&
    operator>>(basic_istream<_CharT, _Traits>& __is, bitset<_Nb>& __x)
    {
      typedef typename _Traits::char_type char_type;
      basic_string<_CharT, _Traits> __tmp;
      __tmp.reserve(_Nb);

      ios_base::iostate __state = ios_base::goodbit;
      typename basic_istream<_CharT, _Traits>::sentry __sentry(__is);
      if (__sentry)
    {
      try
        {
          basic_streambuf<_CharT, _Traits>* __buf = __is.rdbuf();
          // _GLIBCXX_RESOLVE_LIB_DEFECTS
          // 303. Bitset input operator underspecified
          const char_type __zero = __is.widen('0');
          const char_type __one = __is.widen('1');
          for (size_t __i = 0; __i < _Nb; ++__i)
        {
          static typename _Traits::int_type __eof = _Traits::eof();
          
          typename _Traits::int_type __c1 = __buf->sbumpc();
          if (_Traits::eq_int_type(__c1, __eof))
            {
              __state |= ios_base::eofbit;
              break;
            }
          else
            {
              char_type __c2 = _Traits::to_char_type(__c1);
              if (__c2 == __zero)
            __tmp.push_back('0');
              else if (__c2 == __one)
            __tmp.push_back('1');
              else if (_Traits::eq_int_type(__buf->sputbackc(__c2),
                            __eof))
            {
              __state |= ios_base::failbit;
              break;
            }
            }
        }
        }
      catch(...)
        { __is._M_setstate(ios_base::badbit); }
    }

      if (__tmp.empty() && _Nb)
    __state |= ios_base::failbit;
      else
    __x._M_copy_from_string(__tmp, static_cast<size_t>(0), _Nb);
      if (__state)
    __is.setstate(__state);
      return __is;
    }

  template <class _CharT, class _Traits, size_t _Nb>
    basic_ostream<_CharT, _Traits>&
    operator<<(basic_ostream<_CharT, _Traits>& __os, const bitset<_Nb>& __x)
    {
      basic_string<_CharT, _Traits> __tmp;
      __x._M_copy_to_string(__tmp);
      return __os << __tmp;
    }
  //@}
} // namespace std

#undef _GLIBCXX_BITSET_WORDS
#undef _GLIBCXX_BITSET_BITS_PER_WORD

#ifdef _GLIBCXX_DEBUG
# include <debug/bitset>
#endif

#endif /* _GLIBCXX_BITSET */

---