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narrow: Check for changed sign only if types have different signess.

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This commit is contained in:
Paweł Bylica 2016-02-16 14:29:55 +01:00
parent 6a4f2512b7
commit 092a8e53e4
1 changed files with 16 additions and 1 deletions
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17
include/gsl_util.h
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@ -22,6 +22,7 @@
#include "gsl_assert.h" // Ensures/Expects
#include <array>
#include <utility>
#include <type_traits>
#include <exception>
#ifdef _MSC_VER
@ -90,10 +91,24 @@ inline constexpr T narrow_cast(U u) noexcept
struct narrowing_error : public std::exception {};
template<class T, class U>
struct is_same_signess
{
static const bool value =
std::is_signed<T>::value == std::is_signed<U>::value;
};
// narrow() : a checked version of narrow_cast() that throws if the cast changed the value
template<class T, class U>
inline T narrow(U u)
{ T t = narrow_cast<T>(u); if (static_cast<U>(t) != u || (t < T{}) != (u < U{})) throw narrowing_error(); return t; }
{
T t = narrow_cast<T>(u);
if (static_cast<U>(t) != u)
throw narrowing_error();
if (!is_same_signess<T, U>::value && ((t < T{}) != (u < U{})))
throw narrowing_error();
return t;
}
//
// at() - Bounds-checked way of accessing static arrays, std::array, std::vector