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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> | |
b32b8144 FG |
27 | |
28 | namespace boost { | |
29 | namespace random { | |
30 | namespace detail { | |
31 | ||
32 | template<class Engine> | |
33 | inline typename boost::make_unsigned<typename Engine::result_type>::type | |
34 | generate_one_digit(Engine& eng, std::size_t bits) | |
35 | { | |
36 | typedef typename Engine::result_type base_result; | |
37 | typedef typename boost::make_unsigned<base_result>::type base_unsigned; | |
38 | ||
39 | base_unsigned range = | |
40 | detail::subtract<base_result>()((eng.max)(), (eng.min)()); | |
41 | base_unsigned y0_mask = (base_unsigned(2) << (bits - 1)) - 1; | |
42 | base_unsigned y0 = (range + 1) & ~y0_mask; | |
43 | base_unsigned u; | |
44 | do { | |
45 | u = detail::subtract<base_result>()(eng(), (eng.min)()); | |
46 | } while(y0 != 0 && u > base_unsigned(y0 - 1)); | |
47 | return u & y0_mask; | |
48 | } | |
49 | ||
50 | template<class RealType, std::size_t w, class Engine> | |
20effc67 | 51 | std::pair<RealType, int> generate_int_float_pair(Engine& eng, boost::true_type) |
b32b8144 FG |
52 | { |
53 | typedef typename Engine::result_type base_result; | |
54 | typedef typename boost::make_unsigned<base_result>::type base_unsigned; | |
55 | ||
56 | base_unsigned range = | |
57 | detail::subtract<base_result>()((eng.max)(), (eng.min)()); | |
58 | ||
59 | std::size_t m = | |
60 | (range == (std::numeric_limits<base_unsigned>::max)()) ? | |
61 | std::numeric_limits<base_unsigned>::digits : | |
62 | detail::integer_log2(range + 1); | |
63 | ||
64 | int bucket = 0; | |
65 | // process as many full digits as possible into the int part | |
66 | for(std::size_t i = 0; i < w/m; ++i) { | |
67 | base_unsigned u = generate_one_digit(eng, m); | |
68 | bucket = (bucket << m) | u; | |
69 | } | |
70 | RealType r; | |
71 | ||
72 | const std::size_t digits = std::numeric_limits<RealType>::digits; | |
73 | { | |
74 | base_unsigned u = generate_one_digit(eng, m); | |
75 | base_unsigned mask = (base_unsigned(1) << (w%m)) - 1; | |
76 | bucket = (bucket << (w%m)) | (mask & u); | |
77 | const RealType mult = RealType(1)/RealType(base_unsigned(1) << (m - w%m)); | |
78 | // zero out unused bits | |
79 | if (m - w%m > digits) { | |
80 | u &= ~(base_unsigned(1) << (m - digits)); | |
81 | } | |
82 | r = RealType(u >> (w%m)) * mult; | |
83 | } | |
20effc67 | 84 | for(std::size_t i = m - w%m; i + m < digits; i += m) { |
b32b8144 FG |
85 | base_unsigned u = generate_one_digit(eng, m); |
86 | r += u; | |
87 | r *= RealType(0.5)/RealType(base_unsigned(1) << (m - 1)); | |
88 | } | |
89 | if (m - w%m < digits) | |
90 | { | |
91 | const std::size_t remaining = (digits - m + w%m) % m; | |
92 | base_unsigned u = generate_one_digit(eng, m); | |
93 | r += u & ((base_unsigned(2) << (remaining - 1)) - 1); | |
94 | const RealType mult = RealType(0.5)/RealType(base_unsigned(1) << (remaining - 1)); | |
95 | r *= mult; | |
96 | } | |
97 | return std::make_pair(r, bucket); | |
98 | } | |
99 | ||
100 | template<class RealType, std::size_t w, class Engine> | |
20effc67 | 101 | inline std::pair<RealType, int> generate_int_float_pair(Engine& eng, boost::false_type) |
b32b8144 FG |
102 | { |
103 | int bucket = uniform_int_distribution<>(0, (1 << w) - 1)(eng); | |
104 | RealType r = uniform_01<RealType>()(eng); | |
105 | return std::make_pair(r, bucket); | |
106 | } | |
107 | ||
108 | template<class RealType, std::size_t w, class Engine> | |
109 | inline std::pair<RealType, int> generate_int_float_pair(Engine& eng) | |
110 | { | |
111 | typedef typename Engine::result_type base_result; | |
112 | return generate_int_float_pair<RealType, w>(eng, | |
113 | boost::is_integral<base_result>()); | |
114 | } | |
115 | ||
116 | } // namespace detail | |
117 | } // namespace random | |
118 | } // namespace boost | |
119 | ||
120 | #endif // BOOST_RANDOM_DETAIL_INT_FLOAT_PAIR_HPP |