1/* boost random/discard_block.hpp header file
2 *
3 * Copyright Jens Maurer 2002
4 * Copyright Steven Watanabe 2010
5 * Distributed under the Boost Software License, Version 1.0. (See
6 * accompanying file LICENSE_1_0.txt or copy at
7 * http://www.boost.org/LICENSE_1_0.txt)
8 *
9 * See http://www.boost.org for most recent version including documentation.
10 *
11 * $Id$
12 *
13 * Revision history
14 * 2001-03-02 created
15 */
16
17#ifndef BOOST_RANDOM_DISCARD_BLOCK_HPP
18#define BOOST_RANDOM_DISCARD_BLOCK_HPP
19
20#include <iostream>
21#include <boost/config.hpp>
22#include <boost/cstdint.hpp>
23#include <boost/limits.hpp>
24#include <boost/static_assert.hpp>
25#include <boost/random/detail/config.hpp>
26#include <boost/random/detail/seed.hpp>
27#include <boost/random/detail/seed_impl.hpp>
28
29
30namespace boost {
31namespace random {
32
33/**
34 * The class template \discard_block_engine is a model of
35 * \pseudo_random_number_generator. It modifies
36 * another generator by discarding parts of its output.
37 * Out of every block of @c p results, the first @c r
38 * will be returned and the rest discarded.
39 *
40 * Requires: 0 < p <= r
41 */
42template<class UniformRandomNumberGenerator, std::size_t p, std::size_t r>
43class discard_block_engine
44{
45 typedef typename detail::seed_type<
46 typename UniformRandomNumberGenerator::result_type>::type seed_type;
47public:
48 typedef UniformRandomNumberGenerator base_type;
49 typedef typename base_type::result_type result_type;
50
51 BOOST_STATIC_CONSTANT(std::size_t, block_size = p);
52 BOOST_STATIC_CONSTANT(std::size_t, used_block = r);
53
54 BOOST_STATIC_CONSTANT(bool, has_fixed_range = false);
55 BOOST_STATIC_CONSTANT(std::size_t, total_block = p);
56 BOOST_STATIC_CONSTANT(std::size_t, returned_block = r);
57
58 BOOST_STATIC_ASSERT(total_block >= returned_block);
59
60 /** Uses the default seed for the base generator. */
61 discard_block_engine() : _rng(), _n(0) { }
62 /** Constructs a new \discard_block_engine with a copy of rng. */
63 explicit discard_block_engine(const base_type & rng) : _rng(rng), _n(0) { }
64
65#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
66 /** Constructs a new \discard_block_engine with rng. */
67 explicit discard_block_engine(base_type && rng) : _rng(rng), _n(0) { }
68#endif
69
70 /**
71 * Creates a new \discard_block_engine and seeds the underlying
72 * generator with @c value
73 */
74 BOOST_RANDOM_DETAIL_ARITHMETIC_CONSTRUCTOR(discard_block_engine,
75 seed_type, value)
76 { _rng.seed(value); _n = 0; }
77
78 /**
79 * Creates a new \discard_block_engine and seeds the underlying
80 * generator with @c seq
81 */
82 BOOST_RANDOM_DETAIL_SEED_SEQ_CONSTRUCTOR(discard_block_engine, SeedSeq, seq)
83 { _rng.seed(seq); _n = 0; }
84
85 /**
86 * Creates a new \discard_block_engine and seeds the underlying
87 * generator with first and last.
88 */
89 template<class It> discard_block_engine(It& first, It last)
90 : _rng(first, last), _n(0) { }
91
92 /** default seeds the underlying generator. */
93 void seed() { _rng.seed(); _n = 0; }
94 /** Seeds the underlying generator with s. */
95 BOOST_RANDOM_DETAIL_ARITHMETIC_SEED(discard_block_engine, seed_type, s)
96 { _rng.seed(s); _n = 0; }
97 /** Seeds the underlying generator with seq. */
98 BOOST_RANDOM_DETAIL_SEED_SEQ_SEED(discard_block_engine, SeedSeq, seq)
99 { _rng.seed(seq); _n = 0; }
100 /** Seeds the underlying generator with first and last. */
101 template<class It> void seed(It& first, It last)
102 { _rng.seed(first, last); _n = 0; }
103
104 /** Returns the underlying engine. */
105 const base_type& base() const { return _rng; }
106
107 /** Returns the next value of the generator. */
108 result_type operator()()
109 {
110 if(_n >= returned_block) {
111 // discard values of random number generator
112 // Don't use discard, since we still need to
113 // be somewhat compatible with TR1.
114 // _rng.discard(total_block - _n);
115 for(std::size_t i = 0; i < total_block - _n; ++i) {
116 _rng();
117 }
118 _n = 0;
119 }
120 ++_n;
121 return _rng();
122 }
123
124 void discard(boost::uintmax_t z)
125 {
126 for(boost::uintmax_t j = 0; j < z; ++j) {
127 (*this)();
128 }
129 }
130
131 template<class It>
132 void generate(It first, It last)
133 { detail::generate(*this, first, last); }
134
135 /**
136 * Returns the smallest value that the generator can produce.
137 * This is the same as the minimum of the underlying generator.
138 */
139 static result_type min BOOST_PREVENT_MACRO_SUBSTITUTION ()
140 { return (base_type::min)(); }
141 /**
142 * Returns the largest value that the generator can produce.
143 * This is the same as the maximum of the underlying generator.
144 */
145 static result_type max BOOST_PREVENT_MACRO_SUBSTITUTION ()
146 { return (base_type::max)(); }
147
148#ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
149 /** Writes a \discard_block_engine to a @c std::ostream. */
150 template<class CharT, class Traits>
151 friend std::basic_ostream<CharT,Traits>&
152 operator<<(std::basic_ostream<CharT,Traits>& os,
153 const discard_block_engine& s)
154 {
155 os << s._rng << ' ' << s._n;
156 return os;
157 }
158
159 /** Reads a \discard_block_engine from a @c std::istream. */
160 template<class CharT, class Traits>
161 friend std::basic_istream<CharT,Traits>&
162 operator>>(std::basic_istream<CharT,Traits>& is, discard_block_engine& s)
163 {
164 is >> s._rng >> std::ws >> s._n;
165 return is;
166 }
167#endif
168
169 /** Returns true if the two generators will produce identical sequences. */
170 friend bool operator==(const discard_block_engine& x,
171 const discard_block_engine& y)
172 { return x._rng == y._rng && x._n == y._n; }
173 /** Returns true if the two generators will produce different sequences. */
174 friend bool operator!=(const discard_block_engine& x,
175 const discard_block_engine& y)
176 { return !(x == y); }
177
178private:
179 base_type _rng;
180 std::size_t _n;
181};
182
183#ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION
184// A definition is required even for integral static constants
185template<class URNG, std::size_t p, std::size_t r>
186const bool discard_block_engine<URNG, p, r>::has_fixed_range;
187template<class URNG, std::size_t p, std::size_t r>
188const std::size_t discard_block_engine<URNG, p, r>::total_block;
189template<class URNG, std::size_t p, std::size_t r>
190const std::size_t discard_block_engine<URNG, p, r>::returned_block;
191template<class URNG, std::size_t p, std::size_t r>
192const std::size_t discard_block_engine<URNG, p, r>::block_size;
193template<class URNG, std::size_t p, std::size_t r>
194const std::size_t discard_block_engine<URNG, p, r>::used_block;
195#endif
196
197/// \cond \show_deprecated
198
199template<class URNG, int p, int r>
200class discard_block : public discard_block_engine<URNG, p, r>
201{
202 typedef discard_block_engine<URNG, p, r> base_t;
203public:
204 typedef typename base_t::result_type result_type;
205 discard_block() {}
206 template<class T>
207 discard_block(T& arg) : base_t(arg) {}
208 template<class T>
209 discard_block(const T& arg) : base_t(arg) {}
210 template<class It>
211 discard_block(It& first, It last) : base_t(first, last) {}
212 result_type min BOOST_PREVENT_MACRO_SUBSTITUTION ()
213 { return (this->base().min)(); }
214 result_type max BOOST_PREVENT_MACRO_SUBSTITUTION ()
215 { return (this->base().max)(); }
216};
217
218/// \endcond
219
220namespace detail {
221
222 template<class Engine>
223 struct generator_bits;
224
225 template<class URNG, std::size_t p, std::size_t r>
226 struct generator_bits<discard_block_engine<URNG, p, r> > {
227 static std::size_t value() { return generator_bits<URNG>::value(); }
228 };
229
230 template<class URNG, int p, int r>
231 struct generator_bits<discard_block<URNG, p, r> > {
232 static std::size_t value() { return generator_bits<URNG>::value(); }
233 };
234
235}
236
237} // namespace random
238
239} // namespace boost
240
241#endif // BOOST_RANDOM_DISCARD_BLOCK_HPP
242