libcruft-util/cast.hpp

147 lines
4.1 KiB
C++

/*
* 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
*
* 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>
*/
#ifndef __UTIL_CAST_HPP
#define __UTIL_CAST_HPP
#include "debug.hpp"
#include <type_traits>
#include <limits>
namespace util::cast {
///////////////////////////////////////////////////////////////////////////
/// 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 (const U u)
{
CHECK_GE (u, 0);
return static_cast<T> (u);
}
//-------------------------------------------------------------------------
template <
typename T,
typename U
>
std::enable_if_t<
sizeof(T) == sizeof (U) &&
std::is_signed<T>::value &&
std::is_unsigned<U>::value,
T
>
sign (const U u)
{
CHECK_LT (u, std::numeric_limits<U>::max () / 2);
return static_cast<T> (u);
}
///////////////////////////////////////////////////////////////////////////
// cast to a smaller type and check that both values are still equal.
//
// checks will be compiled out if NDEBUG is defined.
template <typename NarrowT, typename WideT>
constexpr NarrowT
narrow (const WideT &val)
{
static_assert (sizeof (NarrowT) <= sizeof (WideT));
static_assert (std::is_signed_v<NarrowT> == std::is_signed_v<WideT>);
#ifndef NDEBUG
auto narrow = static_cast<NarrowT> (val);
CHECK_EQ (narrow, val);
return narrow;
#else
return static_cast<NarrowT> (val);
#endif
}
///////////////////////////////////////////////////////////////////////////
// cast between types checking that equality holds with the result
//
// checks will be compiled out if NDEBUG is defined.
template <typename DstT, typename SrcT>
constexpr DstT
lossless (const SrcT &src)
{
#ifndef NDEBUG
auto dst = static_cast<DstT> (src);
if constexpr (std::is_floating_point_v<SrcT>) {
if (util::is_nan (src)) {
// NaNs must remaing as NaN's. They're important.
CHECK (std::is_floating_point_v<DstT>);
CHECK (std::isnan (dst));
}
}
// Cast dst back to src to check round-trip conversion
// is lossless.
CHECK_EQ (static_cast<SrcT> (dst), src);
return dst;
#else
return static_cast<DstT> (src);
#endif
}
///////////////////////////////////////////////////////////////////////////
/// 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.
template <typename T, typename V>
T*
known (V *v)
{
CHECK (dynamic_cast<T*> (v));
return static_cast<T*> (v);
}
//-------------------------------------------------------------------------
template <typename T, typename V>
T&
known (V &v)
{
CHECK_NOTHROW (dynamic_cast<T> (v));
return static_cast<T> (v);
}
};
#endif