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1 // Boost.Units - A C++ library for zero-overhead dimensional analysis and
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2 // unit/quantity manipulation and conversion
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3 //
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4 // Copyright (C) 2003-2008 Matthias Christian Schabel
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5 // Copyright (C) 2008 Steven Watanabe
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6 //
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7 // Distributed under the Boost Software License, Version 1.0. (See
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8 // accompanying file LICENSE_1_0.txt or copy at
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9 // http://www.boost.org/LICENSE_1_0.txt)
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10
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11 #ifndef BOOST_UNITS_DIM_IMPL_HPP
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12 #define BOOST_UNITS_DIM_IMPL_HPP
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13
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14 #include <boost/mpl/bool.hpp>
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15 #include <boost/mpl/less.hpp>
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16
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17 #include <boost/units/units_fwd.hpp>
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18
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19 /// \file
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20 /// \brief Class encapsulating a dimension tag/value pair
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21
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22 namespace boost {
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23
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24 namespace units {
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25
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26 namespace detail {
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27
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28 struct dim_tag;
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29
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30 }
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31
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32 }
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33
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34 namespace mpl {
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35
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36 /// Less than comparison for sorting @c dim.
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37 template<>
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38 struct less_impl<boost::units::detail::dim_tag, boost::units::detail::dim_tag>
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39 {
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40 template<class T0, class T1>
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41 struct apply : mpl::less<typename T0::tag_type, typename T1::tag_type> {};
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42 };
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43
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44 }
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45
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46 namespace units {
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47
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48 template<class Tag, class Exponent>
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49 struct dim;
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50
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51 template<long N, long D>
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52 class static_rational;
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53
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54 namespace detail {
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55
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56 /// Extract @c tag_type from a @c dim.
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57 template<typename T>
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58 struct get_tag
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59 {
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60 typedef typename T::tag_type type;
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61 };
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62
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63 /// Extract @c value_type from a @c dim.
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64 template<typename T>
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65 struct get_value
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66 {
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67 typedef typename T::value_type type;
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68 };
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69
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70 /// Determine if a @c dim is empty (has a zero exponent).
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71 template<class T>
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72 struct is_empty_dim;
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73
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74 template<typename T>
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75 struct is_empty_dim< dim<T, static_rational<0, 1> > > :
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76 mpl::true_
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77 { };
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78
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79 template<typename T, typename V>
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80 struct is_empty_dim< dim<T, V> > :
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81 mpl::false_
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82 { };
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83
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84 } // namespace detail
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85
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86 } // namespace units
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87
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88 } // namespace boost
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89
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90 #endif // BOOST_UNITS_DIM_IMPL_HPP
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