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New sign_cast implementation using SFINAE

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* Uses enable_if to guarantee same size types for argument/return
* Uses type_traits to check signedness for specialisation
This commit is contained in:
Danny Robson 2011-07-05 22:53:03 +10:00
parent d3c98d479e
commit 6910ef10b9
1 changed files with 29 additions and 17 deletions
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46
types.hpp
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@ -1,6 +1,8 @@
#ifndef __TYPES_HPP
#define __TYPES_HPP
#include "enable_if.hpp"
#include <cstdint>
#include <string>
#include <limits>
@ -106,28 +108,38 @@ template <> struct sign_types <uint64_t> {
};
/// Safely cast a numeric type to its signed comparison, aborting if the
/// result is not representable.
template <typename T>
typename sign_types<T>::with_sign
sign_cast (const typename sign_types<T>::without_sign v)
{
check_hard (v <= std::numeric_limits<typename sign_types<T>::without_sign>::max () >> 1);
return static_cast <typename sign_types<T>::with_sign> (v);
}
/// Safely cast a numeric type to its unsigned comparison, aborting if the
/// result is not representable.
template <typename T>
typename sign_types<T>::without_sign
sign_cast (const typename sign_types<T>::with_sign v)
namespace detail {
template <typename T, typename V>
T
_sign_cast (typename enable_if<sizeof(T) == sizeof(V) &&
std::is_unsigned<T>::value &&
std::is_signed<V>::value, V>::type v)
{
check_hard (v >= 0);
return static_cast <typename sign_types<T>::without_sign> (v);
return static_cast<T> (v);
}
template <typename T, typename V>
T
_sign_cast (typename enable_if<sizeof(T) == sizeof(V) &&
std::is_signed<T>::value &&
std::is_unsigned<V>::value, V>::type v)
{
check_hard (v < std::numeric_limits<V>::max () / 2);
return static_cast<T> (v);
}
}
/// 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.
template <typename T, typename V>
T
sign_cast (V v)
{ return detail::_sign_cast<T,V>(v); }
/// Returns the number of elements of a statically allocated array
template <typename T, size_t N>
size_t elems(T (&)[N])