| 1 | // ----------------------------------------------------------- |
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| 2 | // lowest_bit.hpp |
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| 3 | // |
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| 4 | // Position of the lowest bit 'on' |
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| 5 | // |
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| 6 | // Copyright (c) 2003-2004, 2008 Gennaro Prota |
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| 7 | // |
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| 8 | // Distributed under the Boost Software License, Version 1.0. |
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| 9 | // (See accompanying file LICENSE_1_0.txt or copy at |
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| 10 | // http://www.boost.org/LICENSE_1_0.txt) |
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| 11 | // |
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| 12 | // ----------------------------------------------------------- |
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| 13 | |
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| 14 | #ifndef BOOST_LOWEST_BIT_HPP_GP_20030301 |
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| 15 | #define BOOST_LOWEST_BIT_HPP_GP_20030301 |
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| 16 | |
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| 17 | #include "boost/integer/integer_log2.hpp" |
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| 18 | #include "boost/assert.hpp" |
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| 19 | |
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| 20 | namespace boost { |
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| 21 | namespace detail { |
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| 22 | |
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| 23 | template <typename T> |
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| 24 | int lowest_bit(T x) { |
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| 25 | |
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| 26 | BOOST_ASSERT(x >= 1); // PRE |
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| 27 | |
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| 28 | // clear all bits on except the rightmost one, |
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| 29 | // then calculate the logarithm base 2 |
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| 30 | // |
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| 31 | return boost::integer_log2<T>( x - ( x & (x-1) ) ); |
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| 32 | |
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| 33 | } |
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| 34 | |
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| 35 | } |
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| 36 | } |
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| 37 | |
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| 38 | |
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| 39 | #endif // include guard |
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| 40 | |
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