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include/tl/narrow_cast.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include "tl/detail/prologue.h"
+#include "tl/plain_crash.h"
+#include "tl/type_traits.h"
+
+namespace tl
+{
+
+namespace detail
+{
+
+template <class T, class U>
+struct is_same_signedness : integral_constant<bool, is_signed<T>::value == is_signed<U>::value>
+{
+};
+
+}
+
+template <class T, class U>
+T narrow(U u) noexcept
+{
+    T t = static_cast<T>(u);
+    if (static_cast<U>(t) != u)
+        TL_PLAIN_CRASH("Narrowing error");
+    if (!detail::is_same_signedness<T, U>::value && ((t < T{}) != (u < U{})))
+        TL_PLAIN_CRASH("Narrowing error");
+    return t;
+}
+
+}