65 lines
1.2 KiB
C++
65 lines
1.2 KiB
C++
// boost heap: integer log2
|
|
//
|
|
// Copyright (C) 2010 Tim Blechmann
|
|
//
|
|
// 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)
|
|
|
|
#ifndef BOOST_HEAP_DETAIL_ILOG2_HPP
|
|
#define BOOST_HEAP_DETAIL_ILOG2_HPP
|
|
|
|
#include <string> // std::size_t
|
|
|
|
namespace boost {
|
|
namespace heap {
|
|
namespace detail {
|
|
|
|
template <typename IntType>
|
|
struct log2
|
|
{
|
|
IntType operator()(IntType value)
|
|
{
|
|
IntType l = 0;
|
|
while( (value >> l) > 1 )
|
|
++l;
|
|
return l;
|
|
}
|
|
};
|
|
|
|
#ifdef __GNUC__
|
|
template<>
|
|
struct log2<unsigned int>
|
|
{
|
|
unsigned int operator()(unsigned int value)
|
|
{
|
|
return sizeof(unsigned int)*8 - __builtin_clz(value - 1);
|
|
}
|
|
};
|
|
|
|
template<>
|
|
struct log2<unsigned long>
|
|
{
|
|
unsigned long operator()(unsigned long value)
|
|
{
|
|
return sizeof(unsigned long)*8 - __builtin_clzl(value - 1);
|
|
}
|
|
};
|
|
|
|
#endif
|
|
|
|
} /* namespace detail */
|
|
|
|
|
|
template <typename IntType>
|
|
IntType log2(IntType value)
|
|
{
|
|
detail::log2<IntType> fn;
|
|
return fn(value);
|
|
}
|
|
|
|
} /* namespace heap */
|
|
} /* namespace boost */
|
|
|
|
#endif /* BOOST_HEAP_DETAIL_ILOG2_HPP */
|