139 lines
3.6 KiB
C++
139 lines
3.6 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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///////////////////////////////////////////////////////////////////////////////
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/// Safely cast a numeric type to its (un)signed counterpart, aborting if the
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/// dynamically checked result is not representable. May be optimised out if
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/// NDEBUG is defined.
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///
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/// The signed/unsigned and unsigned/signed cases are split so we can simplify
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/// 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_cast (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_cast (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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#if !defined(NDEBUG)
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/// assert if the value cannot be cast loslessly from U to T, else return the
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/// converted value.Note: this is only a debug-time check and is compiled out
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/// in optimised builds.
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///
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/// relies on equality operators being present and behaving sanely. attempts
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/// to preserve NaN values.
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///
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/// allows the identity cast (if only to make cross-platform porting easier)
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template <typename DstT, typename SrcT>
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constexpr
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std::enable_if_t<
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std::is_arithmetic<SrcT>::value &&
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std::is_arithmetic<DstT>::value,
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DstT
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>
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trunc_cast (const SrcT src)
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{
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auto dst = static_cast<DstT> (src);
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// check if we're testing a NaN by using self-equality. this will not hold
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// for NaN, but makes specialisation easier given we don't need to special
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// case for integers (which don't have std::isnan).
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if (src == src) {
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CHECK_EQ (static_cast<SrcT> (dst), src);
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} else {
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CHECK_NEQ (dst, dst);
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}
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return dst;
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}
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#else
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// in release mode we don't give a fuck what happens. cast away all safety.
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template <typename DstT, typename SrcT>
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DstT
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trunc_cast (const SrcT src)
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{
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return static_cast<DstT> (src);
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}
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#endif
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///////////////////////////////////////////////////////////////////////////////
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/// assert if the value is not a pointer to a subclass of T, else return the
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/// converted value. Note: this is only a debug-time check and is compiled out
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/// in optimised builds.
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template <typename T, typename V>
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T*
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known_cast (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_cast (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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#endif
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