63e88f80
 Hu Chunming
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// 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 */
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