1 /* boost random/detail/int_float_pair.hpp header file
2 *
3 * Copyright Jens Maurer 2000-2001
4 * Copyright Steven Watanabe 2010-2011
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 */
14
15 #ifndef BOOST_RANDOM_DETAIL_INT_FLOAT_PAIR_HPP
16 #define BOOST_RANDOM_DETAIL_INT_FLOAT_PAIR_HPP
17
18 #include <utility>
19 #include <boost/integer.hpp>
20 #include <boost/integer/integer_mask.hpp>
21 #include <boost/type_traits/make_unsigned.hpp>
22 #include <boost/type_traits/is_integral.hpp>
23 #include <boost/random/uniform_01.hpp>
24 #include <boost/random/uniform_int_distribution.hpp>
25 #include <boost/random/detail/signed_unsigned_tools.hpp>
26 #include <boost/random/detail/integer_log2.hpp>
27 #include <boost/mpl/bool.hpp>
28
29 namespace boost {
30 namespace random {
31 namespace detail {
32
33 template<class Engine>
34 inline typename boost::make_unsigned<typename Engine::result_type>::type
generate_one_digit(Engine & eng,std::size_t bits)35 generate_one_digit(Engine& eng, std::size_t bits)
36 {
37 typedef typename Engine::result_type base_result;
38 typedef typename boost::make_unsigned<base_result>::type base_unsigned;
39
40 base_unsigned range =
41 detail::subtract<base_result>()((eng.max)(), (eng.min)());
42 base_unsigned y0_mask = (base_unsigned(2) << (bits - 1)) - 1;
43 base_unsigned y0 = (range + 1) & ~y0_mask;
44 base_unsigned u;
45 do {
46 u = detail::subtract<base_result>()(eng(), (eng.min)());
47 } while(y0 != 0 && u > base_unsigned(y0 - 1));
48 return u & y0_mask;
49 }
50
51 template<class RealType, std::size_t w, class Engine>
generate_int_float_pair(Engine & eng,boost::mpl::true_)52 std::pair<RealType, int> generate_int_float_pair(Engine& eng, boost::mpl::true_)
53 {
54 typedef typename Engine::result_type base_result;
55 typedef typename boost::make_unsigned<base_result>::type base_unsigned;
56
57 base_unsigned range =
58 detail::subtract<base_result>()((eng.max)(), (eng.min)());
59
60 std::size_t m =
61 (range == (std::numeric_limits<base_unsigned>::max)()) ?
62 std::numeric_limits<base_unsigned>::digits :
63 detail::integer_log2(range + 1);
64
65 int bucket = 0;
66 // process as many full digits as possible into the int part
67 for(std::size_t i = 0; i < w/m; ++i) {
68 base_unsigned u = generate_one_digit(eng, m);
69 bucket = (bucket << m) | u;
70 }
71 RealType r;
72
73 const std::size_t digits = std::numeric_limits<RealType>::digits;
74 {
75 base_unsigned u = generate_one_digit(eng, m);
76 base_unsigned mask = (base_unsigned(1) << (w%m)) - 1;
77 bucket = (bucket << (w%m)) | (mask & u);
78 const RealType mult = RealType(1)/RealType(base_unsigned(1) << (m - w%m));
79 // zero out unused bits
80 if (m - w%m > digits) {
81 u &= ~(base_unsigned(1) << (m - digits));
82 }
83 r = RealType(u >> (w%m)) * mult;
84 }
85 for(std::size_t i = m - w%m; i + m < digits; ++i) {
86 base_unsigned u = generate_one_digit(eng, m);
87 r += u;
88 r *= RealType(0.5)/RealType(base_unsigned(1) << (m - 1));
89 }
90 if (m - w%m < digits)
91 {
92 const std::size_t remaining = (digits - m + w%m) % m;
93 base_unsigned u = generate_one_digit(eng, m);
94 r += u & ((base_unsigned(2) << (remaining - 1)) - 1);
95 const RealType mult = RealType(0.5)/RealType(base_unsigned(1) << (remaining - 1));
96 r *= mult;
97 }
98 return std::make_pair(r, bucket);
99 }
100
101 template<class RealType, std::size_t w, class Engine>
generate_int_float_pair(Engine & eng,boost::mpl::false_)102 inline std::pair<RealType, int> generate_int_float_pair(Engine& eng, boost::mpl::false_)
103 {
104 int bucket = uniform_int_distribution<>(0, (1 << w) - 1)(eng);
105 RealType r = uniform_01<RealType>()(eng);
106 return std::make_pair(r, bucket);
107 }
108
109 template<class RealType, std::size_t w, class Engine>
generate_int_float_pair(Engine & eng)110 inline std::pair<RealType, int> generate_int_float_pair(Engine& eng)
111 {
112 typedef typename Engine::result_type base_result;
113 return generate_int_float_pair<RealType, w>(eng,
114 boost::is_integral<base_result>());
115 }
116
117 } // namespace detail
118 } // namespace random
119 } // namespace boost
120
121 #endif // BOOST_RANDOM_DETAIL_INT_FLOAT_PAIR_HPP
122