libcruft-util/cast.hpp

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/*
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* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
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* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2011 Danny Robson <danny@nerdcruft.net>
*/
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#ifndef __UTIL_CAST_HPP
#define __UTIL_CAST_HPP
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#include "./debug.hpp"
#include <type_traits>
#include <limits>
///////////////////////////////////////////////////////////////////////////////
/// Safely cast a numeric type to its (un)signed counterpart, aborting if the
/// dynamically checked result is not representable. May be optimised out if
/// NDEBUG is defined.
///
/// The signed/unsigned and unsigned/signed cases are split so we can simplify
/// the out of range tests.
///
/// The same-type case is not provided because we want to error out on
/// unnecessary casts.
template <
typename T,
typename U
>
std::enable_if_t<
sizeof(T) == sizeof(U) &&
std::is_unsigned<T>::value &&
std::is_signed<U>::value,
T
>
sign_cast (const U u)
{
CHECK_GE (u, 0);
return static_cast<T> (u);
}
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//-----------------------------------------------------------------------------
template <
typename T,
typename U
>
std::enable_if_t<
sizeof(T) == sizeof (U) &&
std::is_signed<T>::value &&
std::is_unsigned<U>::value,
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T
>
sign_cast (const U u)
{
CHECK_LT (u, std::numeric_limits<U>::max () / 2);
return static_cast<T> (u);
}
///----------------------------------------------------------------------------
#if !defined(NDEBUG)
/// assert if the value cannot be cast loslessly from U to T, else return the
/// converted value.Note: this is only a debug-time check and is compiled out
/// in optimised builds.
///
/// relies on equality operators being present and behaving sanely. attempts
/// to preserve NaN values.
///
/// allows the identity cast (if only to make cross-platform porting easier)
template <typename DstT, typename SrcT>
constexpr
std::enable_if_t<
std::is_arithmetic<SrcT>::value &&
std::is_arithmetic<DstT>::value,
DstT
>
trunc_cast (const SrcT src)
{
auto dst = static_cast<DstT> (src);
// check if we're testing a NaN by using self-equality. this will not hold
// for NaN, but makes specialisation easier given we don't need to special
// case for integers (which don't have std::isnan).
if (src == src) {
CHECK_EQ (static_cast<SrcT> (dst), src);
} else {
CHECK_NEQ (dst, dst);
}
return dst;
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}
#else
// in release mode we don't give a fuck what happens. cast away all safety.
template <typename DstT, typename SrcT>
DstT
trunc_cast (const SrcT src)
{
return static_cast<DstT> (src);
}
#endif
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///////////////////////////////////////////////////////////////////////////////
/// assert if the value is not a pointer to a subclass of T, else return the
/// converted value. Note: this is only a debug-time check and is compiled out
/// in optimised builds.
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template <typename T, typename V>
T*
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known_cast (V *v)
{
CHECK (dynamic_cast<T*> (v));
return static_cast<T*> (v);
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}
//-----------------------------------------------------------------------------
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template <typename T, typename V>
T&
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known_cast (V &v)
{
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CHECK_NOTHROW (dynamic_cast<T> (v));
return static_cast<T> (v);
}
#endif