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57 lines
2.0 KiB
Plaintext
57 lines
2.0 KiB
Plaintext
[/
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Copyright 2011 - 2020 John Maddock.
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Copyright 2013 - 2019 Paul A. Bristow.
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Copyright 2013 Christopher Kormanyos.
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Distributed under the Boost Software License, Version 1.0.
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(See 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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]
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[section:internals Internal Support Code]
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There are some traits classes which authors of new backends should be aware of:
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namespace boost{ namespace multiprecision{ namespace detail{
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template<typename From, typename To>
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struct is_explicitly_convertible;
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}}}
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Inherits from `std::integral_constant<bool,true>` if type `From` has an explicit conversion from `To`.
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template <class From, class To>
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struct is_lossy_conversion
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{
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static const bool value = see below;
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};
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Member `value` is true if the conversion from `From` to `To` would result in a loss of precision, and `false` otherwise.
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The default version of this trait simply checks whether the ['kind] of conversion (for example from a floating-point to an integer type)
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is inherently lossy. Note that if either of the types `From` and `To` is of an unknown number category (because `number_category` is not
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specialised for that type) then this trait will be `true`.
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template<typename From, typename To>
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struct is_restricted_conversion
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{
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static const bool value = see below;
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};
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Member `value` is `true` if `From` is only explicitly convertible to `To` and not implicitly convertible, or
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if `is_lossy_conversion<From, To>::value` is `true`. Otherwise `false`.
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Note that while this trait is the ultimate arbiter of which constructors are marked as `explicit` in class `number`,
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authors of backend types should generally specialise one of the traits above, rather than this one directly.
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template <class T>
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is_signed_number;
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template <class T>
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is_unsigned_number;
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These two traits inherit from either `std::integral_constant<bool, true>` or `std::integral_constant<bool, false>`, by default types are assumed to be signed unless
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`is_unsigned_number` is specialized for that type.
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[endsect]
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