[thirdparty/gcc.git] / libstdc++-v3 / include / bits / uniform_int_dist.h

// Class template uniform_int_distribution -*- C++ -*-

// Copyright (C) 2009-2023 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
// <http://www.gnu.org/licenses/>.

/**
 * @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 <type_traits>
#include <ext/numeric_traits.h>
#if __cplusplus > 201703L
# include <concepts>
#endif
#include <bits/concept_check.h> // __glibcxx_function_requires

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#ifdef __cpp_lib_concepts
  /// Requirements for a uniform random bit generator.
  template<typename _Gen>
    concept uniform_random_bit_generator
      = invocable<_Gen&> && unsigned_integral<invoke_result_t<_Gen&>>
      && requires
      {
	{ _Gen::min() } -> same_as<invoke_result_t<_Gen&>>;
	{ _Gen::max() } -> same_as<invoke_result_t<_Gen&>>;
	requires bool_constant<(_Gen::min() < _Gen::max())>::value;
      };
#endif

  namespace __detail
  {
    // Determine whether number is a power of two.
    // This is true for zero, which is OK because we want _Power_of_2(n+1)
    // to be true if n==numeric_limits<_Tp>::max() and so n+1 wraps around.
    template<typename _Tp>
      constexpr bool
      _Power_of_2(_Tp __x)
      {
	return ((__x - 1) & __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<typename _IntType = int>
    class uniform_int_distribution
    {
      static_assert(std::is_integral<_IntType>::value,
		    "template argument must be an integral type");

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

	param_type() : param_type(0) { }

	explicit
	param_type(_IntType __a,
		   _IntType __b = __gnu_cxx::__int_traits<_IntType>::__max)
	: _M_a(__a), _M_b(__b)
	{
	  __glibcxx_assert(_M_a <= _M_b);
	}

	result_type
	a() const
	{ return _M_a; }

	result_type
	b() const
	{ return _M_b; }

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

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

      private:
	_IntType _M_a;
	_IntType _M_b;
      };

    public:
      /**
       * @brief Constructs a uniform distribution object.
       */
      uniform_int_distribution() : uniform_int_distribution(0) { }

      /**
       * @brief Constructs a uniform distribution object.
       */
      explicit
      uniform_int_distribution(_IntType __a,
			       _IntType __b
				 = __gnu_cxx::__int_traits<_IntType>::__max)
      : _M_param(__a, __b)
      { }

      explicit
      uniform_int_distribution(const param_type& __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& __param)
      { _M_param = __param; }

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

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

      /**
       * @brief Generating functions.
       */
      template<typename _UniformRandomBitGenerator>
	result_type
	operator()(_UniformRandomBitGenerator& __urng)
        { return this->operator()(__urng, _M_param); }

      template<typename _UniformRandomBitGenerator>
	result_type
	operator()(_UniformRandomBitGenerator& __urng,
		   const param_type& __p);

      template<typename _ForwardIterator,
	       typename _UniformRandomBitGenerator>
	void
	__generate(_ForwardIterator __f, _ForwardIterator __t,
		   _UniformRandomBitGenerator& __urng)
	{ this->__generate(__f, __t, __urng, _M_param); }

      template<typename _ForwardIterator,
	       typename _UniformRandomBitGenerator>
	void
	__generate(_ForwardIterator __f, _ForwardIterator __t,
		   _UniformRandomBitGenerator& __urng,
		   const param_type& __p)
	{ this->__generate_impl(__f, __t, __urng, __p); }

      template<typename _UniformRandomBitGenerator>
	void
	__generate(result_type* __f, result_type* __t,
		   _UniformRandomBitGenerator& __urng,
		   const param_type& __p)
	{ this->__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& __d1,
		 const uniform_int_distribution& __d2)
      { return __d1._M_param == __d2._M_param; }

    private:
      template<typename _ForwardIterator,
	       typename _UniformRandomBitGenerator>
	void
	__generate_impl(_ForwardIterator __f, _ForwardIterator __t,
			_UniformRandomBitGenerator& __urng,
			const param_type& __p);

      param_type _M_param;

      // Lemire's nearly divisionless algorithm.
      // Returns an unbiased random number from __g downscaled to [0,__range)
      // using an unsigned type _Wp twice as wide as unsigned type _Up.
      template<typename _Wp, typename _Urbg, typename _Up>
	static _Up
	_S_nd(_Urbg& __g, _Up __range)
	{
	  using _Up_traits = __gnu_cxx::__int_traits<_Up>;
	  using _Wp_traits = __gnu_cxx::__int_traits<_Wp>;
	  static_assert(!_Up_traits::__is_signed, "U must be unsigned");
	  static_assert(!_Wp_traits::__is_signed, "W must be unsigned");
	  static_assert(_Wp_traits::__digits == (2 * _Up_traits::__digits),
			"W must be twice as wide as U");

	  // reference: Fast Random Integer Generation in an Interval
	  // ACM Transactions on Modeling and Computer Simulation 29 (1), 2019
	  // https://arxiv.org/abs/1805.10941
	  _Wp __product = _Wp(__g()) * _Wp(__range);
	  _Up __low = _Up(__product);
	  if (__low < __range)
	    {
	      _Up __threshold = -__range % __range;
	      while (__low < __threshold)
		{
		  __product = _Wp(__g()) * _Wp(__range);
		  __low = _Up(__product);
		}
	    }
	  return __product >> _Up_traits::__digits;
	}
    };

  template<typename _IntType>
    template<typename _UniformRandomBitGenerator>
      typename uniform_int_distribution<_IntType>::result_type
      uniform_int_distribution<_IntType>::
      operator()(_UniformRandomBitGenerator& __urng,
		 const param_type& __param)
      {
	typedef typename _UniformRandomBitGenerator::result_type _Gresult_type;
	typedef typename make_unsigned<result_type>::type __utype;
	typedef typename common_type<_Gresult_type, __utype>::type __uctype;

	constexpr __uctype __urngmin = _UniformRandomBitGenerator::min();
	constexpr __uctype __urngmax = _UniformRandomBitGenerator::max();
	static_assert( __urngmin < __urngmax,
	    "Uniform random bit generator must define min() < max()");
	constexpr __uctype __urngrange = __urngmax - __urngmin;

	const __uctype __urange
	  = __uctype(__param.b()) - __uctype(__param.a());

	__uctype __ret;
	if (__urngrange > __urange)
	  {
	    // downscaling

	    const __uctype __uerange = __urange + 1; // __urange can be zero

#if defined __UINT64_TYPE__ && defined __UINT32_TYPE__
#if __SIZEOF_INT128__
	    if _GLIBCXX17_CONSTEXPR (__urngrange == __UINT64_MAX__)
	      {
		// __urng produces values that use exactly 64-bits,
		// so use 128-bit integers to downscale to desired range.
		__UINT64_TYPE__ __u64erange = __uerange;
		__ret = __extension__ _S_nd<unsigned __int128>(__urng,
							       __u64erange);
	      }
	    else
#endif
	    if _GLIBCXX17_CONSTEXPR (__urngrange == __UINT32_MAX__)
	      {
		// __urng produces values that use exactly 32-bits,
		// so use 64-bit integers to downscale to desired range.
		__UINT32_TYPE__ __u32erange = __uerange;
		__ret = _S_nd<__UINT64_TYPE__>(__urng, __u32erange);
	      }
	    else
#endif
	      {
		// fallback case (2 divisions)
		const __uctype __scaling = __urngrange / __uerange;
		const __uctype __past = __uerange * __scaling;
		do
		  __ret = __uctype(__urng()) - __urngmin;
		while (__ret >= __past);
		__ret /= __scaling;
	      }
	  }
	else if (__urngrange < __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 > __urange || __ret < __tmp);
	  }
	else
	  __ret = __uctype(__urng()) - __urngmin;

	return __ret + __param.a();
      }


  template<typename _IntType>
    template<typename _ForwardIterator,
	     typename _UniformRandomBitGenerator>
      void
      uniform_int_distribution<_IntType>::
      __generate_impl(_ForwardIterator __f, _ForwardIterator __t,
		      _UniformRandomBitGenerator& __urng,
		      const param_type& __param)
      {
	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
	typedef typename _UniformRandomBitGenerator::result_type _Gresult_type;
	typedef typename make_unsigned<result_type>::type __utype;
	typedef typename common_type<_Gresult_type, __utype>::type __uctype;

	static_assert( __urng.min() < __urng.max(),
	    "Uniform random bit generator must define min() < max()");

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

	__uctype __ret;

	if (__urngrange > __urange)
	  {
	    if (__detail::_Power_of_2(__urngrange + 1)
		&& __detail::_Power_of_2(__urange + 1))
	      {
		while (__f != __t)
		  {
		    __ret = __uctype(__urng()) - __urngmin;
		    *__f++ = (__ret & __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 >= __past);
		    *__f++ = __ret / __scaling + __param.a();
		  }
	      }
	  }
	else if (__urngrange < __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
		  {
		    constexpr __uctype __uerngrange = __urngrange + 1;
		    __tmp = (__uerngrange * operator()
			     (__urng, param_type(0, __urange / __uerngrange)));
		    __ret = __tmp + (__uctype(__urng()) - __urngmin);
		  }
		while (__ret > __urange || __ret < __tmp);
		*__f++ = __ret;
	      }
	  }
	else
	  while (__f != __t)
	    *__f++ = __uctype(__urng()) - __urngmin + __param.a();
      }

  // operator!= and operator<< and operator>> are defined in <bits/random.h>

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif
Commit	Line	Data
2944621e JW	1	// Class template uniform_int_distribution -- C++ --
2944621e JW	2
83ffe9cd	3	// Copyright (C) 2009-2023 Free Software Foundation, Inc.
2944621e JW	4	//
	5	// This file is part of the GNU ISO C++ Library. This library is free
	6	// software; you can redistribute it and/or modify it under the
	7	// terms of the GNU General Public License as published by the
	8	// Free Software Foundation; either version 3, or (at your option)
	9	// any later version.
	10
	11	// This library is distributed in the hope that it will be useful,
	12	// but WITHOUT ANY WARRANTY; without even the implied warranty of
	13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	14	// GNU General Public License for more details.
	15
	16	// Under Section 7 of GPL version 3, you are granted additional
	17	// permissions described in the GCC Runtime Library Exception, version
	18	// 3.1, as published by the Free Software Foundation.
	19
	20	// You should have received a copy of the GNU General Public License and
	21	// a copy of the GCC Runtime Library Exception along with this program;
	22	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
	23	// <http://www.gnu.org/licenses/>.
	24
	25	/**
	26	* @file bits/uniform_int_dist.h
	27	* This is an internal header file, included by other library headers.
	28	* Do not attempt to use it directly. @headername{random}
	29	*/
	30
	31	#ifndef _GLIBCXX_BITS_UNIFORM_INT_DIST_H
	32	#define _GLIBCXX_BITS_UNIFORM_INT_DIST_H
	33
	34	#include <type_traits>
9af65c2b	35	#include <ext/numeric_traits.h>
9cd4eeef JW	36	#if __cplusplus > 201703L
	37	# include <concepts>
	38	#endif
47cca028	39	#include <bits/concept_check.h> // __glibcxx_function_requires
2944621e JW	40
	41	namespace std _GLIBCXX_VISIBILITY(default)
	42	{
4a15d842	43	_GLIBCXX_BEGIN_NAMESPACE_VERSION
2944621e	44
9cd4eeef JW	45	#ifdef __cpp_lib_concepts
	46	/// Requirements for a uniform random bit generator.
	47	template<typename _Gen>
	48	concept uniform_random_bit_generator
	49	= invocable<_Gen&> && unsigned_integral<invoke_result_t<_Gen&>>
	50	&& requires
	51	{
	52	{ _Gen::min() } -> same_as<invoke_result_t<_Gen&>>;
	53	{ _Gen::max() } -> same_as<invoke_result_t<_Gen&>>;
	54	requires bool_constant<(_Gen::min() < _Gen::max())>::value;
	55	};
	56	#endif
	57
2944621e JW	58	namespace __detail
2944621e JW	59	{
b2b85163 JW	60	// Determine whether number is a power of two.
	61	// This is true for zero, which is OK because we want _Power_of_2(n+1)
	62	// to be true if n==numeric_limits<_Tp>::max() and so n+1 wraps around.
2944621e	63	template<typename _Tp>
822c1d21	64	constexpr bool
2944621e JW	65	_Power_of_2(_Tp __x)
	66	{
	67	return ((__x - 1) & __x) == 0;
071f228f	68	}
2944621e JW	69	}
	70
	71	/**
	72	* @brief Uniform discrete distribution for random numbers.
	73	* A discrete random distribution on the range @f$[min, max]@f$ with equal
	74	* probability throughout the range.
	75	*/
	76	template<typename _IntType = int>
	77	class uniform_int_distribution
	78	{
	79	static_assert(std::is_integral<_IntType>::value,
0cded43d	80	"template argument must be an integral type");
2944621e JW	81
	82	public:
	83	/** The type of the range of the distribution. */
	84	typedef _IntType result_type;
	85	/** Parameter type. */
	86	struct param_type
	87	{
	88	typedef uniform_int_distribution<_IntType> distribution_type;
	89
977ac63e JW	90	param_type() : param_type(0) { }
977ac63e JW	91
2944621e	92	explicit
977ac63e	93	param_type(_IntType __a,
9af65c2b	94	_IntType __b = __gnu_cxx::__int_traits<_IntType>::__max)
2944621e JW	95	: _M_a(__a), _M_b(__b)
	96	{
	97	__glibcxx_assert(_M_a <= _M_b);
	98	}
	99
	100	result_type
	101	a() const
	102	{ return _M_a; }
	103
	104	result_type
	105	b() const
	106	{ return _M_b; }
	107
	108	friend bool
	109	operator==(const param_type& __p1, const param_type& __p2)
	110	{ return __p1._M_a == __p2._M_a && __p1._M_b == __p2._M_b; }
	111
12905f10 JW	112	friend bool
	113	operator!=(const param_type& __p1, const param_type& __p2)
	114	{ return !(__p1 == __p2); }
	115
2944621e JW	116	private:
	117	_IntType _M_a;
	118	_IntType _M_b;
	119	};
	120
	121	public:
dd9db6f8 JW	122	/**
	123	* @brief Constructs a uniform distribution object.
	124	*/
	125	uniform_int_distribution() : uniform_int_distribution(0) { }
	126
2944621e JW	127	/**
	128	* @brief Constructs a uniform distribution object.
	129	*/
	130	explicit
dd9db6f8	131	uniform_int_distribution(_IntType __a,
9af65c2b JW	132	_IntType __b
9af65c2b JW	133	= __gnu_cxx::__int_traits<_IntType>::__max)
2944621e JW	134	: _M_param(__a, __b)
	135	{ }
	136
	137	explicit
	138	uniform_int_distribution(const param_type& __p)
	139	: _M_param(__p)
	140	{ }
	141
	142	/**
	143	* @brief Resets the distribution state.
	144	*
	145	* Does nothing for the uniform integer distribution.
	146	*/
	147	void
	148	reset() { }
	149
	150	result_type
	151	a() const
	152	{ return _M_param.a(); }
	153
	154	result_type
	155	b() const
	156	{ return _M_param.b(); }
	157
	158	/**
	159	* @brief Returns the parameter set of the distribution.
	160	*/
	161	param_type
	162	param() const
	163	{ return _M_param; }
	164
	165	/**
	166	* @brief Sets the parameter set of the distribution.
	167	* @param __param The new parameter set of the distribution.
	168	*/
	169	void
	170	param(const param_type& __param)
	171	{ _M_param = __param; }
	172
	173	/**
	174	* @brief Returns the inclusive lower bound of the distribution range.
	175	*/
	176	result_type
	177	min() const
	178	{ return this->a(); }
	179
	180	/**
	181	* @brief Returns the inclusive upper bound of the distribution range.
	182	*/
	183	result_type
	184	max() const
	185	{ return this->b(); }
	186
	187	/**
	188	* @brief Generating functions.
	189	*/
68990ed1	190	template<typename _UniformRandomBitGenerator>
2944621e	191	result_type
68990ed1	192	operator()(_UniformRandomBitGenerator& __urng)
2944621e JW	193	{ return this->operator()(__urng, _M_param); }
2944621e JW	194
68990ed1	195	template<typename _UniformRandomBitGenerator>
2944621e	196	result_type
68990ed1	197	operator()(_UniformRandomBitGenerator& __urng,
2944621e JW	198	const param_type& __p);
	199
	200	template<typename _ForwardIterator,
68990ed1	201	typename _UniformRandomBitGenerator>
2944621e JW	202	void
2944621e JW	203	__generate(_ForwardIterator __f, _ForwardIterator __t,
68990ed1	204	_UniformRandomBitGenerator& __urng)
2944621e JW	205	{ this->__generate(__f, __t, __urng, _M_param); }
	206
	207	template<typename _ForwardIterator,
68990ed1	208	typename _UniformRandomBitGenerator>
2944621e JW	209	void
2944621e JW	210	__generate(_ForwardIterator __f, _ForwardIterator __t,
68990ed1	211	_UniformRandomBitGenerator& __urng,
2944621e JW	212	const param_type& __p)
	213	{ this->__generate_impl(__f, __t, __urng, __p); }
	214
68990ed1	215	template<typename _UniformRandomBitGenerator>
2944621e JW	216	void
2944621e JW	217	__generate(result_type* __f, result_type* __t,
68990ed1	218	_UniformRandomBitGenerator& __urng,
2944621e JW	219	const param_type& __p)
	220	{ this->__generate_impl(__f, __t, __urng, __p); }
	221
	222	/**
	223	* @brief Return true if two uniform integer distributions have
	224	* the same parameters.
	225	*/
	226	friend bool
	227	operator==(const uniform_int_distribution& __d1,
	228	const uniform_int_distribution& __d2)
	229	{ return __d1._M_param == __d2._M_param; }
	230
	231	private:
	232	template<typename _ForwardIterator,
68990ed1	233	typename _UniformRandomBitGenerator>
2944621e JW	234	void
2944621e JW	235	__generate_impl(_ForwardIterator __f, _ForwardIterator __t,
68990ed1	236	_UniformRandomBitGenerator& __urng,
2944621e JW	237	const param_type& __p);
	238
	239	param_type _M_param;
98c37d3b DL	240
	241	// Lemire's nearly divisionless algorithm.
	242	// Returns an unbiased random number from __g downscaled to [0,__range)
	243	// using an unsigned type _Wp twice as wide as unsigned type _Up.
	244	template<typename _Wp, typename _Urbg, typename _Up>
	245	static _Up
	246	_S_nd(_Urbg& __g, _Up __range)
	247	{
822c1d21 JW	248	using _Up_traits = __gnu_cxx::__int_traits<_Up>;
	249	using _Wp_traits = __gnu_cxx::__int_traits<_Wp>;
	250	static_assert(!_Up_traits::__is_signed, "U must be unsigned");
	251	static_assert(!_Wp_traits::__is_signed, "W must be unsigned");
	252	static_assert(_Wp_traits::__digits == (2 * _Up_traits::__digits),
	253	"W must be twice as wide as U");
98c37d3b DL	254
	255	// reference: Fast Random Integer Generation in an Interval
	256	// ACM Transactions on Modeling and Computer Simulation 29 (1), 2019
	257	// https://arxiv.org/abs/1805.10941
	258	_Wp __product = _Wp(__g()) * _Wp(__range);
	259	_Up __low = _Up(__product);
	260	if (__low < __range)
	261	{
	262	_Up __threshold = -__range % __range;
	263	while (__low < __threshold)
	264	{
	265	__product = _Wp(__g()) * _Wp(__range);
	266	__low = _Up(__product);
	267	}
	268	}
822c1d21	269	return __product >> _Up_traits::__digits;
98c37d3b	270	}
2944621e JW	271	};
	272
	273	template<typename _IntType>
68990ed1	274	template<typename _UniformRandomBitGenerator>
2944621e JW	275	typename uniform_int_distribution<_IntType>::result_type
2944621e JW	276	uniform_int_distribution<_IntType>::
68990ed1	277	operator()(_UniformRandomBitGenerator& __urng,
2944621e JW	278	const param_type& __param)
2944621e JW	279	{
68990ed1 JW	280	typedef typename _UniformRandomBitGenerator::result_type _Gresult_type;
	281	typedef typename make_unsigned<result_type>::type __utype;
	282	typedef typename common_type<_Gresult_type, __utype>::type __uctype;
2944621e	283
24366207 JW	284	constexpr __uctype __urngmin = _UniformRandomBitGenerator::min();
	285	constexpr __uctype __urngmax = _UniformRandomBitGenerator::max();
	286	static_assert( __urngmin < __urngmax,
822c1d21	287	"Uniform random bit generator must define min() < max()");
822c1d21	288	constexpr __uctype __urngrange = __urngmax - __urngmin;
24366207	289
2944621e JW	290	const __uctype __urange
	291	= __uctype(__param.b()) - __uctype(__param.a());
	292
	293	__uctype __ret;
2944621e JW	294	if (__urngrange > __urange)
	295	{
	296	// downscaling
98c37d3b	297
2944621e	298	const __uctype __uerange = __urange + 1; // __urange can be zero
98c37d3b	299
822c1d21	300	#if defined __UINT64_TYPE__ && defined __UINT32_TYPE__
98c37d3b	301	#if __SIZEOF_INT128__
822c1d21	302	if _GLIBCXX17_CONSTEXPR (__urngrange == __UINT64_MAX__)
98c37d3b	303	{
822c1d21 JW	304	// __urng produces values that use exactly 64-bits,
	305	// so use 128-bit integers to downscale to desired range.
	306	__UINT64_TYPE__ __u64erange = __uerange;
42167831 JW	307	__ret = __extension__ _S_nd<unsigned __int128>(__urng,
42167831 JW	308	__u64erange);
98c37d3b DL	309	}
	310	else
	311	#endif
822c1d21	312	if _GLIBCXX17_CONSTEXPR (__urngrange == __UINT32_MAX__)
98c37d3b	313	{
822c1d21 JW	314	// __urng produces values that use exactly 32-bits,
	315	// so use 64-bit integers to downscale to desired range.
	316	__UINT32_TYPE__ __u32erange = __uerange;
	317	__ret = _S_nd<__UINT64_TYPE__>(__urng, __u32erange);
98c37d3b DL	318	}
98c37d3b DL	319	else
822c1d21	320	#endif
98c37d3b DL	321	{
	322	// fallback case (2 divisions)
	323	const __uctype __scaling = __urngrange / __uerange;
	324	const __uctype __past = __uerange * __scaling;
	325	do
	326	__ret = __uctype(__urng()) - __urngmin;
	327	while (__ret >= __past);
	328	__ret /= __scaling;
	329	}
2944621e JW	330	}
	331	else if (__urngrange < __urange)
	332	{
	333	// upscaling
	334	/*
	335	Note that every value in [0, urange]
	336	can be written uniquely as
	337
	338	(urngrange + 1) * high + low
	339
	340	where
	341
	342	high in [0, urange / (urngrange + 1)]
	343
	344	and
	345
	346	low in [0, urngrange].
	347	*/
	348	__uctype __tmp; // wraparound control
	349	do
	350	{
	351	const __uctype __uerngrange = __urngrange + 1;
	352	__tmp = (__uerngrange * operator()
	353	(__urng, param_type(0, __urange / __uerngrange)));
	354	__ret = __tmp + (__uctype(__urng()) - __urngmin);
	355	}
	356	while (__ret > __urange \|\| __ret < __tmp);
	357	}
	358	else
	359	__ret = __uctype(__urng()) - __urngmin;
	360
	361	return __ret + __param.a();
	362	}
	363
	364
	365	template<typename _IntType>
	366	template<typename _ForwardIterator,
68990ed1	367	typename _UniformRandomBitGenerator>
2944621e JW	368	void
	369	uniform_int_distribution<_IntType>::
	370	__generate_impl(_ForwardIterator __f, _ForwardIterator __t,
68990ed1	371	_UniformRandomBitGenerator& __urng,
2944621e JW	372	const param_type& __param)
	373	{
	374	__glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
68990ed1 JW	375	typedef typename _UniformRandomBitGenerator::result_type _Gresult_type;
	376	typedef typename make_unsigned<result_type>::type __utype;
	377	typedef typename common_type<_Gresult_type, __utype>::type __uctype;
2944621e	378
822c1d21 JW	379	static_assert( __urng.min() < __urng.max(),
	380	"Uniform random bit generator must define min() < max()");
	381
	382	constexpr __uctype __urngmin = __urng.min();
	383	constexpr __uctype __urngmax = __urng.max();
	384	constexpr __uctype __urngrange = __urngmax - __urngmin;
2944621e JW	385	const __uctype __urange
	386	= __uctype(__param.b()) - __uctype(__param.a());
	387
	388	__uctype __ret;
	389
	390	if (__urngrange > __urange)
	391	{
	392	if (__detail::_Power_of_2(__urngrange + 1)
	393	&& __detail::_Power_of_2(__urange + 1))
	394	{
	395	while (__f != __t)
	396	{
	397	__ret = __uctype(__urng()) - __urngmin;
	398	*__f++ = (__ret & __urange) + __param.a();
	399	}
	400	}
	401	else
	402	{
	403	// downscaling
	404	const __uctype __uerange = __urange + 1; // __urange can be zero
	405	const __uctype __scaling = __urngrange / __uerange;
	406	const __uctype __past = __uerange * __scaling;
	407	while (__f != __t)
	408	{
	409	do
	410	__ret = __uctype(__urng()) - __urngmin;
	411	while (__ret >= __past);
	412	*__f++ = __ret / __scaling + __param.a();
	413	}
	414	}
	415	}
	416	else if (__urngrange < __urange)
	417	{
	418	// upscaling
	419	/*
	420	Note that every value in [0, urange]
	421	can be written uniquely as
	422
	423	(urngrange + 1) * high + low
	424
	425	where
	426
	427	high in [0, urange / (urngrange + 1)]
	428
	429	and
	430
	431	low in [0, urngrange].
	432	*/
	433	__uctype __tmp; // wraparound control
	434	while (__f != __t)
	435	{
	436	do
	437	{
822c1d21	438	constexpr __uctype __uerngrange = __urngrange + 1;
2944621e JW	439	__tmp = (__uerngrange * operator()
	440	(__urng, param_type(0, __urange / __uerngrange)));
	441	__ret = __tmp + (__uctype(__urng()) - __urngmin);
	442	}
	443	while (__ret > __urange \|\| __ret < __tmp);
	444	*__f++ = __ret;
	445	}
	446	}
	447	else
	448	while (__f != __t)
	449	*__f++ = __uctype(__urng()) - __urngmin + __param.a();
	450	}
	451
12905f10 JW	452	// operator!= and operator<< and operator>> are defined in <bits/random.h>
12905f10 JW	453
2944621e JW	454	_GLIBCXX_END_NAMESPACE_VERSION
	455	} // namespace std
	456
	457	#endif