<h2>Editing File: /usr/include/c++/8/bits/uniform_int_dist.h</h2><form method='post'><textarea name='content' class='file-edit'>// Class template uniform_int_distribution -*- C++ -*-

// Copyright (C) 2009-2018 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 3, 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// &lt;http://www.gnu.org/licenses/&gt;.

/**
 * @file bits/uniform_int_dist.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{random}
 */

#ifndef _GLIBCXX_BITS_UNIFORM_INT_DIST_H
#define _GLIBCXX_BITS_UNIFORM_INT_DIST_H

#include &lt;type_traits&gt;
#include &lt;limits&gt;

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  namespace __detail
  {
    /* Determine whether number is a power of 2.  */
    template&lt;typename _Tp&gt;
      inline bool
      _Power_of_2(_Tp __x)
      {
	return ((__x - 1) &amp; __x) == 0;
      }
  }

  /**
   * @brief Uniform discrete distribution for random numbers.
   * A discrete random distribution on the range @f$[min, max]@f$ with equal
   * probability throughout the range.
   */
  template&lt;typename _IntType = int&gt;
    class uniform_int_distribution
    {
      static_assert(std::is_integral&lt;_IntType&gt;::value,
		    &quot;template argument must be an integral type&quot;);

    public:
      /** The type of the range of the distribution. */
      typedef _IntType result_type;
      /** Parameter type. */
      struct param_type
      {
	typedef uniform_int_distribution&lt;_IntType&gt; distribution_type;

	explicit
	param_type(_IntType __a = 0,
		   _IntType __b = std::numeric_limits&lt;_IntType&gt;::max())
	: _M_a(__a), _M_b(__b)
	{
	  __glibcxx_assert(_M_a &lt;= _M_b);
	}

	result_type
	a() const
	{ return _M_a; }

	result_type
	b() const
	{ return _M_b; }

	friend bool
	operator==(const param_type&amp; __p1, const param_type&amp; __p2)
	{ return __p1._M_a == __p2._M_a &amp;&amp; __p1._M_b == __p2._M_b; }

	friend bool
	operator!=(const param_type&amp; __p1, const param_type&amp; __p2)
	{ return !(__p1 == __p2); }

      private:
	_IntType _M_a;
	_IntType _M_b;
      };

    public:
      /**
       * @brief Constructs a uniform distribution object.
       */
      explicit
      uniform_int_distribution(_IntType __a = 0,
			   _IntType __b = std::numeric_limits&lt;_IntType&gt;::max())
      : _M_param(__a, __b)
      { }

      explicit
      uniform_int_distribution(const param_type&amp; __p)
      : _M_param(__p)
      { }

      /**
       * @brief Resets the distribution state.
       *
       * Does nothing for the uniform integer distribution.
       */
      void
      reset() { }

      result_type
      a() const
      { return _M_param.a(); }

      result_type
      b() const
      { return _M_param.b(); }

      /**
       * @brief Returns the parameter set of the distribution.
       */
      param_type
      param() const
      { return _M_param; }

      /**
       * @brief Sets the parameter set of the distribution.
       * @param __param The new parameter set of the distribution.
       */
      void
      param(const param_type&amp; __param)
      { _M_param = __param; }

      /**
       * @brief Returns the inclusive lower bound of the distribution range.
       */
      result_type
      min() const
      { return this-&gt;a(); }

      /**
       * @brief Returns the inclusive upper bound of the distribution range.
       */
      result_type
      max() const
      { return this-&gt;b(); }

      /**
       * @brief Generating functions.
       */
      template&lt;typename _UniformRandomNumberGenerator&gt;
	result_type
	operator()(_UniformRandomNumberGenerator&amp; __urng)
        { return this-&gt;operator()(__urng, _M_param); }

      template&lt;typename _UniformRandomNumberGenerator&gt;
	result_type
	operator()(_UniformRandomNumberGenerator&amp; __urng,
		   const param_type&amp; __p);

      template&lt;typename _ForwardIterator,
	       typename _UniformRandomNumberGenerator&gt;
	void
	__generate(_ForwardIterator __f, _ForwardIterator __t,
		   _UniformRandomNumberGenerator&amp; __urng)
	{ this-&gt;__generate(__f, __t, __urng, _M_param); }

      template&lt;typename _ForwardIterator,
	       typename _UniformRandomNumberGenerator&gt;
	void
	__generate(_ForwardIterator __f, _ForwardIterator __t,
		   _UniformRandomNumberGenerator&amp; __urng,
		   const param_type&amp; __p)
	{ this-&gt;__generate_impl(__f, __t, __urng, __p); }

      template&lt;typename _UniformRandomNumberGenerator&gt;
	void
	__generate(result_type* __f, result_type* __t,
		   _UniformRandomNumberGenerator&amp; __urng,
		   const param_type&amp; __p)
	{ this-&gt;__generate_impl(__f, __t, __urng, __p); }

      /**
       * @brief Return true if two uniform integer distributions have
       *        the same parameters.
       */
      friend bool
      operator==(const uniform_int_distribution&amp; __d1,
		 const uniform_int_distribution&amp; __d2)
      { return __d1._M_param == __d2._M_param; }

    private:
      template&lt;typename _ForwardIterator,
	       typename _UniformRandomNumberGenerator&gt;
	void
	__generate_impl(_ForwardIterator __f, _ForwardIterator __t,
			_UniformRandomNumberGenerator&amp; __urng,
			const param_type&amp; __p);

      param_type _M_param;
    };

  template&lt;typename _IntType&gt;
    template&lt;typename _UniformRandomNumberGenerator&gt;
      typename uniform_int_distribution&lt;_IntType&gt;::result_type
      uniform_int_distribution&lt;_IntType&gt;::
      operator()(_UniformRandomNumberGenerator&amp; __urng,
		 const param_type&amp; __param)
      {
	typedef typename _UniformRandomNumberGenerator::result_type
	  _Gresult_type;
	typedef typename std::make_unsigned&lt;result_type&gt;::type __utype;
	typedef typename std::common_type&lt;_Gresult_type, __utype&gt;::type
	  __uctype;

	const __uctype __urngmin = __urng.min();
	const __uctype __urngmax = __urng.max();
	const __uctype __urngrange = __urngmax - __urngmin;
	const __uctype __urange
	  = __uctype(__param.b()) - __uctype(__param.a());

	__uctype __ret;

	if (__urngrange &gt; __urange)
	  {
	    // downscaling
	    const __uctype __uerange = __urange + 1; // __urange can be zero
	    const __uctype __scaling = __urngrange / __uerange;
	    const __uctype __past = __uerange * __scaling;
	    do
	      __ret = __uctype(__urng()) - __urngmin;
	    while (__ret &gt;= __past);
	    __ret /= __scaling;
	  }
	else if (__urngrange &lt; __urange)
	  {
	    // upscaling
	    /*
	      Note that every value in [0, urange]
	      can be written uniquely as

	      (urngrange + 1) * high + low

	      where

	      high in [0, urange / (urngrange + 1)]

	      and

	      low in [0, urngrange].
	    */
	    __uctype __tmp; // wraparound control
	    do
	      {
		const __uctype __uerngrange = __urngrange + 1;
		__tmp = (__uerngrange * operator()
			 (__urng, param_type(0, __urange / __uerngrange)));
		__ret = __tmp + (__uctype(__urng()) - __urngmin);
	      }
	    while (__ret &gt; __urange || __ret &lt; __tmp);
	  }
	else
	  __ret = __uctype(__urng()) - __urngmin;

	return __ret + __param.a();
      }


  template&lt;typename _IntType&gt;
    template&lt;typename _ForwardIterator,
	     typename _UniformRandomNumberGenerator&gt;
      void
      uniform_int_distribution&lt;_IntType&gt;::
      __generate_impl(_ForwardIterator __f, _ForwardIterator __t,
		      _UniformRandomNumberGenerator&amp; __urng,
		      const param_type&amp; __param)
      {
	__glibcxx_function_requires(_ForwardIteratorConcept&lt;_ForwardIterator&gt;)
	typedef typename _UniformRandomNumberGenerator::result_type
	  _Gresult_type;
	typedef typename std::make_unsigned&lt;result_type&gt;::type __utype;
	typedef typename std::common_type&lt;_Gresult_type, __utype&gt;::type
	  __uctype;

	const __uctype __urngmin = __urng.min();
	const __uctype __urngmax = __urng.max();
	const __uctype __urngrange = __urngmax - __urngmin;
	const __uctype __urange
	  = __uctype(__param.b()) - __uctype(__param.a());

	__uctype __ret;

	if (__urngrange &gt; __urange)
	  {
	    if (__detail::_Power_of_2(__urngrange + 1)
		&amp;&amp; __detail::_Power_of_2(__urange + 1))
	      {
		while (__f != __t)
		  {
		    __ret = __uctype(__urng()) - __urngmin;
		    *__f++ = (__ret &amp; __urange) + __param.a();
		  }
	      }
	    else
	      {
		// downscaling
		const __uctype __uerange = __urange + 1; // __urange can be zero
		const __uctype __scaling = __urngrange / __uerange;
		const __uctype __past = __uerange * __scaling;
		while (__f != __t)
		  {
		    do
		      __ret = __uctype(__urng()) - __urngmin;
		    while (__ret &gt;= __past);
		    *__f++ = __ret / __scaling + __param.a();
		  }
	      }
	  }
	else if (__urngrange &lt; __urange)
	  {
	    // upscaling
	    /*
	      Note that every value in [0, urange]
	      can be written uniquely as

	      (urngrange + 1) * high + low

	      where

	      high in [0, urange / (urngrange + 1)]

	      and

	      low in [0, urngrange].
	    */
	    __uctype __tmp; // wraparound control
	    while (__f != __t)
	      {
		do
		  {
		    const __uctype __uerngrange = __urngrange + 1;
		    __tmp = (__uerngrange * operator()
			     (__urng, param_type(0, __urange / __uerngrange)));
		    __ret = __tmp + (__uctype(__urng()) - __urngmin);
		  }
		while (__ret &gt; __urange || __ret &lt; __tmp);
		*__f++ = __ret;
	      }
	  }
	else
	  while (__f != __t)
	    *__f++ = __uctype(__urng()) - __urngmin + __param.a();
      }

  // operator!= and operator&lt;&lt; and operator&gt;&gt; are defined in &lt;bits/random.h&gt;

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif
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