ext/functional

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// Functional extensions -*- C++ -*-

// Copyright (C) 2002 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) 1994
 * Hewlett-Packard Company
 *
 * 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.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996
 * 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 ext/functional
 *  This file is a GNU extension to the Standard C++ Library (possibly
 *  containing extensions from the HP/SGI STL subset).  You should only
 *  include this header if you are using GCC 3 or later.
 */

#ifndef _EXT_FUNCTIONAL
#define _EXT_FUNCTIONAL 1

#pragma GCC system_header

#include <functional>

namespace __gnu_cxx
{
using std::unary_function;
using std::binary_function;
using std::mem_fun1_t;
using std::const_mem_fun1_t;
using std::mem_fun1_ref_t;
using std::const_mem_fun1_ref_t;

/** The @c identity_element functions are not part of the C++ standard; SGI
 *  provided them as an extension.  Its argument is an operation, and its
 *  return value is the identity element for that operation.  It is overloaded
 *  for addition and multiplication, and you can overload it for your own
 *  nefarious operations.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Tp> inline _Tp identity_element(std::plus<_Tp>) {
  return _Tp(0);
}
/// An \link SGIextensions SGI extension \endlink.
template <class _Tp> inline _Tp identity_element(std::multiplies<_Tp>) {
  return _Tp(1);
}
/** @}  */

/** As an extension to the binders, SGI provided composition functors and
 *  wrapper functions to aid in their creation.  The @c unary_compose
 *  functor is constructed from two functions/functors, @c f and @c g.
 *  Calling @c operator() with a single argument @c x returns @c f(g(x)).
 *  The function @c compose1 takes the two functions and constructs a
 *  @c unary_compose variable for you.
 *
 *  @c binary_compose is constructed from three functors, @c f, @c g1,
 *  and @c g2.  Its @c operator() returns @c f(g1(x),g2(x)).  The function
 *  @compose2 takes f, g1, and g2, and constructs the @c binary_compose
 *  instance for you.  For example, if @c f returns an int, then
 *  \code
 *  int answer = (compose2(f,g1,g2))(x);
 *  \endcode
 *  is equivalent to
 *  \code
 *  int temp1 = g1(x);
 *  int temp2 = g2(x);
 *  int answer = f(temp1,temp2);
 *  \endcode
 *  But the first form is more compact, and can be passed around as a
 *  functor to other algorithms.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2>
class unary_compose
  : public unary_function<typename _Operation2::argument_type,
               typename _Operation1::result_type>
{
protected:
  _Operation1 _M_fn1;
  _Operation2 _M_fn2;
public:
  unary_compose(const _Operation1& __x, const _Operation2& __y)
    : _M_fn1(__x), _M_fn2(__y) {}
  typename _Operation1::result_type
  operator()(const typename _Operation2::argument_type& __x) const {
    return _M_fn1(_M_fn2(__x));
  }
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2>
inline unary_compose<_Operation1,_Operation2>
compose1(const _Operation1& __fn1, const _Operation2& __fn2)
{
  return unary_compose<_Operation1,_Operation2>(__fn1, __fn2);
}

/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2, class _Operation3>
class binary_compose
  : public unary_function<typename _Operation2::argument_type,
                          typename _Operation1::result_type> {
protected:
  _Operation1 _M_fn1;
  _Operation2 _M_fn2;
  _Operation3 _M_fn3;
public:
  binary_compose(const _Operation1& __x, const _Operation2& __y,
                 const _Operation3& __z)
    : _M_fn1(__x), _M_fn2(__y), _M_fn3(__z) { }
  typename _Operation1::result_type
  operator()(const typename _Operation2::argument_type& __x) const {
    return _M_fn1(_M_fn2(__x), _M_fn3(__x));
  }
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Operation1, class _Operation2, class _Operation3>
inline binary_compose<_Operation1, _Operation2, _Operation3>
compose2(const _Operation1& __fn1, const _Operation2& __fn2,
         const _Operation3& __fn3)
{
  return binary_compose<_Operation1,_Operation2,_Operation3>
    (__fn1, __fn2, __fn3);
}
/** @}  */

/** As an extension, SGI provided a functor called @c identity.  When a
 *  functor is required but no operations are desired, this can be used as a
 *  pass-through.  Its @c operator() returns its argument unchanged.
 *
 *  @addtogroup SGIextensions
*/
template <class _Tp> struct identity : public std::_Identity<_Tp> {};

/** @c select1st and @c select2nd are extensions provided by SGI.  Their
 *  @c operator()s
 *  take a @c std::pair as an argument, and return either the first member
 *  or the second member, respectively.  They can be used (especially with
 *  the composition functors) to "strip" data from a sequence before
 *  performing the remainder of an algorithm.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Pair> struct select1st : public std::_Select1st<_Pair> {};
/// An \link SGIextensions SGI extension \endlink.
template <class _Pair> struct select2nd : public std::_Select2nd<_Pair> {};
/** @}  */

// extension documented next
template <class _Arg1, class _Arg2>
struct _Project1st : public binary_function<_Arg1, _Arg2, _Arg1> {
  _Arg1 operator()(const _Arg1& __x, const _Arg2&) const { return __x; }
};

template <class _Arg1, class _Arg2>
struct _Project2nd : public binary_function<_Arg1, _Arg2, _Arg2> {
  _Arg2 operator()(const _Arg1&, const _Arg2& __y) const { return __y; }
};

/** The @c operator() of the @c project1st functor takes two arbitrary
 *  arguments and returns the first one, while @c project2nd returns the
 *  second one.  They are extensions provided by SGI.
 *
 *  @addtogroup SGIextensions
 *  @{
*/

/// An \link SGIextensions SGI extension \endlink.
template <class _Arg1, class _Arg2>
struct project1st : public _Project1st<_Arg1, _Arg2> {};

/// An \link SGIextensions SGI extension \endlink.
template <class _Arg1, class _Arg2>
struct project2nd : public _Project2nd<_Arg1, _Arg2> {};
/** @}  */

// extension documented next
template <class _Result>
struct _Constant_void_fun {
  typedef _Result result_type;
  result_type _M_val;

  _Constant_void_fun(const result_type& __v) : _M_val(__v) {}
  const result_type& operator()() const { return _M_val; }
};

template <class _Result, class _Argument>
struct _Constant_unary_fun {
  typedef _Argument argument_type;
  typedef  _Result  result_type;
  result_type _M_val;

  _Constant_unary_fun(const result_type& __v) : _M_val(__v) {}
  const result_type& operator()(const _Argument&) const { return _M_val; }
};

template <class _Result, class _Arg1, class _Arg2>
struct _Constant_binary_fun {
  typedef  _Arg1   first_argument_type;
  typedef  _Arg2   second_argument_type;
  typedef  _Result result_type;
  _Result _M_val;

  _Constant_binary_fun(const _Result& __v) : _M_val(__v) {}
  const result_type& operator()(const _Arg1&, const _Arg2&) const {
    return _M_val;
  }
};

/** These three functors are each constructed from a single arbitrary
 *  variable/value.  Later, their @c operator()s completely ignore any
 *  arguments passed, and return the stored value.
 *  - @c constant_void_fun's @c operator() takes no arguments
 *  - @c constant_unary_fun's @c operator() takes one argument (ignored)
 *  - @c constant_binary_fun's @c operator() takes two arguments (ignored)
 *
 *  The helper creator functions @c constant0, @c constant1, and
 *  @c constant2 each take a "result" argument and construct variables of
 *  the appropriate functor type.
 *
 *  @addtogroup SGIextensions
 *  @{
*/
/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
struct constant_void_fun : public _Constant_void_fun<_Result> {
  constant_void_fun(const _Result& __v) : _Constant_void_fun<_Result>(__v) {}
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Result,
          class _Argument = _Result>
struct constant_unary_fun : public _Constant_unary_fun<_Result, _Argument>
{
  constant_unary_fun(const _Result& __v)
    : _Constant_unary_fun<_Result, _Argument>(__v) {}
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Result,
          class _Arg1 = _Result,
          class _Arg2 = _Arg1>
struct constant_binary_fun
  : public _Constant_binary_fun<_Result, _Arg1, _Arg2>
{
  constant_binary_fun(const _Result& __v)
    : _Constant_binary_fun<_Result, _Arg1, _Arg2>(__v) {}
};

/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
inline constant_void_fun<_Result> constant0(const _Result& __val)
{
  return constant_void_fun<_Result>(__val);
}

/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
inline constant_unary_fun<_Result,_Result> constant1(const _Result& __val)
{
  return constant_unary_fun<_Result,_Result>(__val);
}

/// An \link SGIextensions SGI extension \endlink.
template <class _Result>
inline constant_binary_fun<_Result,_Result,_Result>
constant2(const _Result& __val)
{
  return constant_binary_fun<_Result,_Result,_Result>(__val);
}
/** @}  */

/** The @c subtractive_rng class is documented on
 *  <a href="http://www.sgi.com/tech/stl/">SGI's site</a>.
 *  Note that this code assumes that @c int is 32 bits.
 *
 *  @ingroup SGIextensions
*/
class subtractive_rng : public unary_function<unsigned int, unsigned int> {
private:
  unsigned int _M_table[55];
  size_t _M_index1;
  size_t _M_index2;
public:
  /// Returns a number less than the argument.
  unsigned int operator()(unsigned int __limit) {
    _M_index1 = (_M_index1 + 1) % 55;
    _M_index2 = (_M_index2 + 1) % 55;
    _M_table[_M_index1] = _M_table[_M_index1] - _M_table[_M_index2];
    return _M_table[_M_index1] % __limit;
  }

  void _M_initialize(unsigned int __seed)
  {
    unsigned int __k = 1;
    _M_table[54] = __seed;
    size_t __i;
    for (__i = 0; __i < 54; __i++) {
        size_t __ii = (21 * (__i + 1) % 55) - 1;
        _M_table[__ii] = __k;
        __k = __seed - __k;
        __seed = _M_table[__ii];
    }
    for (int __loop = 0; __loop < 4; __loop++) {
        for (__i = 0; __i < 55; __i++)
            _M_table[__i] = _M_table[__i] - _M_table[(1 + __i + 30) % 55];
    }
    _M_index1 = 0;
    _M_index2 = 31;
  }

  /// Ctor allowing you to initialize the seed.
  subtractive_rng(unsigned int __seed) { _M_initialize(__seed); }
  /// Default ctor; initializes its state with some number you don't see.
  subtractive_rng() { _M_initialize(161803398u); }
};

// Mem_fun adaptor helper functions mem_fun1 and mem_fun1_ref,
// provided for backward compatibility, they are no longer part of
// the C++ standard.

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_t<_Ret,_Tp,_Arg> mem_fun1(_Ret (_Tp::*__f)(_Arg))
  { return mem_fun1_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_t<_Ret,_Tp,_Arg> mem_fun1(_Ret (_Tp::*__f)(_Arg) const)
  { return const_mem_fun1_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_ref_t<_Ret,_Tp,_Arg> mem_fun1_ref(_Ret (_Tp::*__f)(_Arg))
  { return mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f); }

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_ref_t<_Ret,_Tp,_Arg>
mem_fun1_ref(_Ret (_Tp::*__f)(_Arg) const)
  { return const_mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f); }
} // namespace __gnu_cxx

#endif

---