147 lines
4.1 KiB
C++
147 lines
4.1 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2011 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef __UTIL_CAST_HPP
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#define __UTIL_CAST_HPP
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#include "debug.hpp"
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#include <type_traits>
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#include <limits>
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namespace util::cast {
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///////////////////////////////////////////////////////////////////////////
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/// Safely cast a numeric type to its (un)signed counterpart, aborting if
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/// the dynamically checked result is not representable. May be optimised
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/// out if NDEBUG is defined.
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///
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/// The signed/unsigned and unsigned/signed cases are split so we can
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/// simplify the out of range tests.
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///
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/// The same-type case is not provided because we want to error out on
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/// unnecessary casts.
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template <
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typename T,
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typename U
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>
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std::enable_if_t<
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sizeof(T) == sizeof(U) &&
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std::is_unsigned<T>::value &&
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std::is_signed<U>::value,
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T
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>
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sign (const U u)
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{
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CHECK_GE (u, 0);
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return static_cast<T> (u);
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}
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//-------------------------------------------------------------------------
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template <
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typename T,
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typename U
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>
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std::enable_if_t<
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sizeof(T) == sizeof (U) &&
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std::is_signed<T>::value &&
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std::is_unsigned<U>::value,
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T
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>
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sign (const U u)
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{
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CHECK_LT (u, std::numeric_limits<U>::max () / 2);
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return static_cast<T> (u);
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}
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///////////////////////////////////////////////////////////////////////////
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// cast to a smaller type and check that both values are still equal.
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//
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// checks will be compiled out if NDEBUG is defined.
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template <typename NarrowT, typename WideT>
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constexpr NarrowT
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narrow (const WideT &val)
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{
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static_assert (sizeof (NarrowT) <= sizeof (WideT));
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static_assert (std::is_signed_v<NarrowT> == std::is_signed_v<WideT>);
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#ifndef NDEBUG
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auto narrow = static_cast<NarrowT> (val);
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CHECK_EQ (narrow, val);
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return narrow;
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#else
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return static_cast<NarrowT> (val);
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#endif
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}
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///////////////////////////////////////////////////////////////////////////
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// cast between types checking that equality holds with the result
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//
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// checks will be compiled out if NDEBUG is defined.
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template <typename DstT, typename SrcT>
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constexpr DstT
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lossless (const SrcT &src)
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{
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#ifndef NDEBUG
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auto dst = static_cast<DstT> (src);
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if constexpr (std::is_floating_point_v<SrcT>) {
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if (util::is_nan (src)) {
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// NaNs must remaing as NaN's. They're important.
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CHECK (std::is_floating_point_v<DstT>);
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CHECK (std::isnan (dst));
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}
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}
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// Cast dst back to src to check round-trip conversion
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// is lossless.
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CHECK_EQ (static_cast<SrcT> (dst), src);
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return dst;
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#else
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return static_cast<DstT> (src);
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#endif
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}
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///////////////////////////////////////////////////////////////////////////
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/// assert if the value is not a pointer to a subclass of T, else return
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/// the converted value. Note: this is only a debug-time check and is
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/// compiled out in optimised builds.
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template <typename T, typename V>
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T*
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known (V *v)
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{
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CHECK (dynamic_cast<T*> (v));
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return static_cast<T*> (v);
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}
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//-------------------------------------------------------------------------
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template <typename T, typename V>
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T&
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known (V &v)
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{
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CHECK_NOTHROW (dynamic_cast<T> (v));
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return static_cast<T> (v);
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}
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};
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#endif
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