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ircd::util: Add constexpr kronecker delta.

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This commit is contained in:
Jason Volk 2017-08-23 14:58:21 -06:00
parent 3d536d26b6
commit 7197491364
1 changed files with 54 additions and 0 deletions
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54
include/ircd/util.h
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@ -377,6 +377,60 @@ runtil(std::tuple<args...> &t,
return runtil<size>(t, std::forward<func>(f));
}
//
// Kronecker delta
//
template<size_t j,
size_t i,
class func,
class... args>
constexpr
typename std::enable_if<i == j, void>::type
kronecker_delta(const std::tuple<args...> &t,
func&& f)
{
using value_type = typename std::tuple_element<i, std::tuple<args...>>::type;
f(static_cast<const value_type &>(std::get<i>(t)));
}
template<size_t i,
size_t j,
class func,
class... args>
constexpr
typename std::enable_if<i == j, void>::type
kronecker_delta(std::tuple<args...> &t,
func&& f)
{
using value_type = typename std::tuple_element<i, std::tuple<args...>>::type;
f(static_cast<value_type &>(std::get<i>(t)));
}
template<size_t j,
size_t i = 0,
class func,
class... args>
constexpr
typename std::enable_if<(i < j), void>::type
kronecker_delta(const std::tuple<args...> &t,
func&& f)
{
kronecker_delta<j, i + 1>(t, std::forward<func>(f));
}
template<size_t j,
size_t i = 0,
class func,
class... args>
constexpr
typename std::enable_if<(i < j), void>::type
kronecker_delta(std::tuple<args...> &t,
func&& f)
{
kronecker_delta<j, i + 1>(t, std::forward<func>(f));
}
// For conforming enums include a _NUM_ as the last element,
// then num_of<my_enum>() works