85 lines
2.2 KiB
C++
85 lines
2.2 KiB
C++
/* boost random/detail/integer_log2.hpp header file
|
|
*
|
|
* Copyright Steven Watanabe 2011
|
|
* Distributed under the Boost Software License, Version 1.0. (See
|
|
* accompanying file LICENSE_1_0.txt or copy at
|
|
* http://www.boost.org/LICENSE_1_0.txt)
|
|
*
|
|
* See http://www.boost.org for most recent version including documentation.
|
|
*
|
|
* $Id$
|
|
*
|
|
*/
|
|
|
|
#ifndef BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
|
|
#define BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
|
|
|
|
#include <boost/config.hpp>
|
|
#include <boost/limits.hpp>
|
|
#include <boost/pending/integer_log2.hpp>
|
|
|
|
namespace boost {
|
|
namespace random {
|
|
namespace detail {
|
|
|
|
#if !defined(BOOST_NO_CXX11_CONSTEXPR)
|
|
#define BOOST_RANDOM_DETAIL_CONSTEXPR constexpr
|
|
#elif defined(BOOST_MSVC)
|
|
#define BOOST_RANDOM_DETAIL_CONSTEXPR __forceinline
|
|
#elif defined(__GNUC__) && __GNUC__ >= 4
|
|
#define BOOST_RANDOM_DETAIL_CONSTEXPR inline __attribute__((__const__)) __attribute__((__always_inline__))
|
|
#else
|
|
#define BOOST_RANDOM_DETAIL_CONSTEXPR inline
|
|
#endif
|
|
|
|
template<int Shift>
|
|
struct integer_log2_impl
|
|
{
|
|
#if defined(BOOST_NO_CXX11_CONSTEXPR)
|
|
template<class T>
|
|
BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
|
|
{
|
|
int update = ((t >> Shift) != 0) * Shift;
|
|
return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update);
|
|
}
|
|
#else
|
|
template<class T>
|
|
BOOST_RANDOM_DETAIL_CONSTEXPR static int apply2(T t, int accum, int update)
|
|
{
|
|
return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update);
|
|
}
|
|
|
|
template<class T>
|
|
BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
|
|
{
|
|
return apply2(t, accum, ((t >> Shift) != 0) * Shift);
|
|
}
|
|
#endif
|
|
};
|
|
|
|
template<>
|
|
struct integer_log2_impl<1>
|
|
{
|
|
template<class T>
|
|
BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
|
|
{
|
|
return int(t >> 1) + accum;
|
|
}
|
|
};
|
|
|
|
template<class T>
|
|
BOOST_RANDOM_DETAIL_CONSTEXPR int integer_log2(T t)
|
|
{
|
|
return integer_log2_impl<
|
|
::boost::detail::max_pow2_less<
|
|
::std::numeric_limits<T>::digits, 4
|
|
>::value
|
|
>::apply(t, 0);
|
|
}
|
|
|
|
} // namespace detail
|
|
} // namespace random
|
|
} // namespace boost
|
|
|
|
#endif // BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
|