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cast: allow trunc_cast to same type

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this makes templated code slightly easier to write
This commit is contained in:
Danny Robson 2016-10-25 17:48:55 +11:00
parent e5d44d0c6d
commit 6781f7a361
1 changed files with 29 additions and 24 deletions
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55
cast.hpp
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@ -68,6 +68,7 @@ sign_cast (const U u)
///---------------------------------------------------------------------------- ///----------------------------------------------------------------------------
#if !defined(NDEBUG)
/// assert if the value cannot be cast loslessly from U to T, else return the /// 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 /// converted value.Note: this is only a debug-time check and is compiled out
/// in optimised builds. /// in optimised builds.
@ -76,37 +77,41 @@ sign_cast (const U u)
/// to preserve NaN values. /// to preserve NaN values.
/// ///
/// allows the identity cast (if only to make cross-platform porting easier) /// allows the identity cast (if only to make cross-platform porting easier)
template < template <typename DstT, typename SrcT>
typename T, constexpr
typename U
>
std::enable_if_t< std::enable_if_t<
// only enabled for builtin types. there's no reason this couldn't be std::is_arithmetic<SrcT>::value &&
// extended, but we've only really tested on integers and floats. std::is_arithmetic<DstT>::value,
std::is_fundamental<T>::value && std::is_fundamental<U>::value && ( DstT
// either we're casting between real and integer
std::is_floating_point<T>::value != std::is_floating_point<U>::value
// or we're reducing the size of the type
|| sizeof (T) <= sizeof (U)
),
T
> >
trunc_cast (const U &u) trunc_cast (const SrcT src)
{ {
auto t = static_cast<T> (u); auto dst = static_cast<DstT> (src);
// if we're not a NaN then check equality by casting U-to-T-to-U. we can't // check if we're testing a NaN by using self-equality. this will not hold
// explicitly check isnan because that call isn't valid for arbitrary // for NaN, but makes specialisation easier given we don't need to special
// types and we'll cause a compile-time error. // case for integers (which don't have std::isnan).
if (u == u) if (src == src) {
CHECK_EQ (static_cast<U> (t), u); CHECK_EQ (static_cast<SrcT> (dst), src);
// we must be a NaN. test that t is a NaN too by self-equality. } else {
else CHECK_NEQ (dst, dst);
CHECK_NEQ (t, t);
return t;
} }
return dst;
}
#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
/////////////////////////////////////////////////////////////////////////////// ///////////////////////////////////////////////////////////////////////////////
/// assert if the value is not a pointer to a subclass of T, else return the /// assert if the value is not a pointer to a subclass of T, else return the