186 lines
9.4 KiB
C++
186 lines
9.4 KiB
C++
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// Boost.Units - A C++ library for zero-overhead dimensional analysis and
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// unit/quantity manipulation and conversion
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//
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// Copyright (C) 2003-2008 Matthias Christian Schabel
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// Copyright (C) 2007-2008 Steven Watanabe
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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_UNITS_CONVERSION_HPP
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#define BOOST_UNITS_CONVERSION_HPP
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/// \file
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/// \brief Template for defining conversions between quantities.
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#include <boost/units/detail/conversion_impl.hpp>
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namespace boost {
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namespace units {
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template<class From, class To>
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struct conversion_helper;
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#ifdef BOOST_UNITS_DOXYGEN
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/// Template for defining conversions between
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/// quantities. This template should be specialized
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/// for every quantity that allows conversions.
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/// For example, if you have a two units
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/// called pair and dozen you would write
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/// @code
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/// namespace boost {
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/// namespace units {
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/// template<class T0, class T1>
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/// struct conversion_helper<quantity<dozen, T0>, quantity<pair, T1> >
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/// {
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/// static quantity<pair, T1> convert(const quantity<dozen, T0>& source)
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/// {
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/// return(quantity<pair, T1>::from_value(6 * source.value()));
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/// }
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/// };
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/// }
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/// }
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/// @endcode
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///
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/// In most cases, the predefined specializations for @c unit
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/// and @c absolute should be sufficient, so users should rarely
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/// need to use this.
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template<class From, class To>
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struct conversion_helper
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{
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static To convert(const From&);
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};
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#endif
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/// Defines the conversion factor from a base unit to any unit
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/// or to another base unit with the correct dimensions. Uses
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/// of this macro must appear at global scope.
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/// If the destination unit is a base unit or a unit that contains
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/// only one base unit which is raised to the first power (e.g. feet->meters)
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/// the reverse (meters->feet in this example) need not be defined explicitly.
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#define BOOST_UNITS_DEFINE_CONVERSION_FACTOR(Source, Destination, type_, value_) \
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namespace boost { \
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namespace units { \
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template<> \
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struct select_base_unit_converter< \
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unscale<Source>::type, \
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unscale<reduce_unit<Destination::unit_type>::type>::type \
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> \
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{ \
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typedef Source source_type; \
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typedef reduce_unit<Destination::unit_type>::type destination_type; \
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}; \
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template<> \
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struct base_unit_converter<Source, reduce_unit<Destination::unit_type>::type> \
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{ \
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static const bool is_defined = true; \
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typedef type_ type; \
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static type value() { return(value_); } \
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}; \
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} \
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} \
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void boost_units_require_semicolon()
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/// Defines the conversion factor from a base unit to any other base
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/// unit with the same dimensions. Params should be a Boost.Preprocessor
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/// Seq of template parameters, such as (class T1)(class T2)
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/// All uses of must appear at global scope. The reverse conversion will
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/// be defined automatically. This macro is a little dangerous, because,
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/// unlike the non-template form, it will silently fail if either base
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/// unit is scaled. This is probably not an issue if both the source
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/// and destination types depend on the template parameters, but be aware
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/// that a generic conversion to kilograms is not going to work.
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#define BOOST_UNITS_DEFINE_CONVERSION_FACTOR_TEMPLATE(Params, Source, Destination, type_, value_) \
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namespace boost { \
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namespace units { \
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template<BOOST_PP_SEQ_ENUM(Params)> \
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struct base_unit_converter< \
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Source, \
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BOOST_UNITS_MAKE_HETEROGENEOUS_UNIT(Destination, typename Source::dimension_type)\
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> \
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{ \
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static const bool is_defined = true; \
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typedef type_ type; \
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static type value() { return(value_); } \
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}; \
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} \
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} \
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void boost_units_require_semicolon()
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/// Specifies the default conversion to be applied when
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/// no direct conversion is available.
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/// Source is a base unit. Dest is any unit with the
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/// same dimensions.
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#define BOOST_UNITS_DEFAULT_CONVERSION(Source, Dest) \
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namespace boost { \
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namespace units { \
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template<> \
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struct unscaled_get_default_conversion<unscale<Source>::type> \
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{ \
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static const bool is_defined = true; \
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typedef Dest::unit_type type; \
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}; \
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} \
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} \
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void boost_units_require_semicolon()
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/// Specifies the default conversion to be applied when
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/// no direct conversion is available.
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/// Params is a PP Sequence of template arguments.
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/// Source is a base unit. Dest is any unit with the
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/// same dimensions. The source must not be a scaled
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/// base unit.
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#define BOOST_UNITS_DEFAULT_CONVERSION_TEMPLATE(Params, Source, Dest) \
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namespace boost { \
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namespace units { \
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template<BOOST_PP_SEQ_ENUM(Params)> \
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struct unscaled_get_default_conversion<Source> \
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{ \
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static const bool is_defined = true; \
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typedef typename Dest::unit_type type; \
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}; \
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} \
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} \
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void boost_units_require_semicolon()
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/// INTERNAL ONLY
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/// Users should not create their units in namespace boost::units.
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/// If we want to make this public it needs to allow better control over
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/// the namespaces. --SJW.
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/// template that defines a base_unit and conversion to another dimensionally-consistent unit
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#define BOOST_UNITS_DEFINE_BASE_UNIT_WITH_CONVERSIONS(namespace_, name_, name_string_, symbol_string_, factor, unit, id)\
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namespace boost { \
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namespace units { \
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namespace namespace_ { \
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struct name_ ## _base_unit \
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: base_unit<name_ ## _base_unit, unit::dimension_type, id> { \
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static const char* name() { return(name_string_); } \
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static const char* symbol() { return(symbol_string_); } \
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}; \
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} \
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} \
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} \
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BOOST_UNITS_DEFINE_CONVERSION_FACTOR(namespace_::name_ ## _base_unit, unit, double, factor); \
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BOOST_UNITS_DEFAULT_CONVERSION(namespace_::name_ ## _base_unit, unit)
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/// Find the conversion factor between two units.
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template<class FromUnit,class ToUnit>
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inline
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typename one_to_double_type<
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typename detail::conversion_factor_helper<FromUnit, ToUnit>::type
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>::type
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conversion_factor(const FromUnit&,const ToUnit&)
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{
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return(one_to_double(detail::conversion_factor_helper<FromUnit, ToUnit>::value()));
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}
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} // namespace units
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} // namespace boost
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#endif // BOOST_UNITS_CONVERSION_HPP
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