1 | /* boost random/detail/integer_log2.hpp header file |
2 | * |
3 | * Copyright Steven Watanabe 2011 |
4 | * Distributed under the Boost Software License, Version 1.0. (See |
5 | * accompanying file LICENSE_1_0.txt or copy at |
6 | * http://www.boost.org/LICENSE_1_0.txt) |
7 | * |
8 | * See http://www.boost.org for most recent version including documentation. |
9 | * |
10 | * $Id$ |
11 | * |
12 | */ |
13 | |
14 | #ifndef BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP |
15 | #define BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP |
16 | |
17 | #include <boost/config.hpp> |
18 | #include <boost/limits.hpp> |
19 | #include <boost/pending/integer_log2.hpp> |
20 | |
21 | namespace boost { |
22 | namespace random { |
23 | namespace detail { |
24 | |
25 | #if !defined(BOOST_NO_CXX11_CONSTEXPR) |
26 | #define BOOST_RANDOM_DETAIL_CONSTEXPR constexpr |
27 | #elif defined(BOOST_MSVC) |
28 | #define BOOST_RANDOM_DETAIL_CONSTEXPR __forceinline |
29 | #elif defined(__GNUC__) && __GNUC__ >= 4 |
30 | #define BOOST_RANDOM_DETAIL_CONSTEXPR inline __attribute__((__const__)) __attribute__((__always_inline__)) |
31 | #else |
32 | #define BOOST_RANDOM_DETAIL_CONSTEXPR inline |
33 | #endif |
34 | |
35 | template<int Shift> |
36 | struct integer_log2_impl |
37 | { |
38 | #if defined(BOOST_NO_CXX11_CONSTEXPR) |
39 | template<class T> |
40 | BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum) |
41 | { |
42 | int update = ((t >> Shift) != 0) * Shift; |
43 | return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update); |
44 | } |
45 | #else |
46 | template<class T> |
47 | BOOST_RANDOM_DETAIL_CONSTEXPR static int apply2(T t, int accum, int update) |
48 | { |
49 | return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update); |
50 | } |
51 | |
52 | template<class T> |
53 | BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum) |
54 | { |
55 | return apply2(t, accum, ((t >> Shift) != 0) * Shift); |
56 | } |
57 | #endif |
58 | }; |
59 | |
60 | template<> |
61 | struct integer_log2_impl<1> |
62 | { |
63 | template<class T> |
64 | BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum) |
65 | { |
66 | return int(t >> 1) + accum; |
67 | } |
68 | }; |
69 | |
70 | template<class T> |
71 | BOOST_RANDOM_DETAIL_CONSTEXPR int integer_log2(T t) |
72 | { |
73 | return integer_log2_impl< |
74 | ::boost::detail::max_pow2_less< |
75 | ::std::numeric_limits<T>::digits, 4 |
76 | >::value |
77 | >::apply(t, 0); |
78 | } |
79 | |
80 | } // namespace detail |
81 | } // namespace random |
82 | } // namespace boost |
83 | |
84 | #endif // BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP |
85 | |