65 lines
1.2 KiB
C++
65 lines
1.2 KiB
C++
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// boost heap: integer log2
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//
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// Copyright (C) 2010 Tim Blechmann
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_HEAP_DETAIL_ILOG2_HPP
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#define BOOST_HEAP_DETAIL_ILOG2_HPP
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#include <string> // std::size_t
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namespace boost {
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namespace heap {
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namespace detail {
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template <typename IntType>
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struct log2
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{
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IntType operator()(IntType value)
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{
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IntType l = 0;
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while( (value >> l) > 1 )
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++l;
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return l;
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}
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};
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#ifdef __GNUC__
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template<>
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struct log2<unsigned int>
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{
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unsigned int operator()(unsigned int value)
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{
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return sizeof(unsigned int)*8 - __builtin_clz(value - 1);
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}
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};
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template<>
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struct log2<unsigned long>
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{
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unsigned long operator()(unsigned long value)
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{
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return sizeof(unsigned long)*8 - __builtin_clzl(value - 1);
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}
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};
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#endif
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} /* namespace detail */
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template <typename IntType>
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IntType log2(IntType value)
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{
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detail::log2<IntType> fn;
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return fn(value);
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}
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} /* namespace heap */
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} /* namespace boost */
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#endif /* BOOST_HEAP_DETAIL_ILOG2_HPP */
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