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#pragma once
#include <tuple>
namespace intgemm {
/*
* Sequence of unsigned integers
*
* Examples:
* sequence<1, 2, 3>()
* sequence_pushback<4, sequence<1, 2, 3>>() = sequence<1, 2, 3, 4>()
* sequence_popfront<sequence<1, 2, 3>>() = sequence<2, 3>()
* make_sequence<3>() = sequence<0, 1, 2>()
*/
template <unsigned... Indices>
struct sequence { using type = sequence; };
template <unsigned I, typename Sequence>
struct sequence_pushback;
template <unsigned I, unsigned... Indices>
struct sequence_pushback<I, sequence<Indices...>> : sequence<Indices..., I> {};
template <typename Sequence>
struct sequence_popfront;
template <unsigned FirstIndex, unsigned... RestIndices>
struct sequence_popfront<sequence<FirstIndex, RestIndices...>> : sequence<RestIndices...> {};
namespace { // anonymous namespace
template <unsigned N>
struct make_sequence_impl : sequence_pushback<N - 1, typename make_sequence_impl<N - 1>::type> {};
template <>
struct make_sequence_impl<0> : sequence<> {};
} // anonymous namespace
template <unsigned N>
using make_sequence = typename make_sequence_impl<N>::type;
/*
* Make a subtuple
*/
template <typename Tuple, unsigned... Indices>
using subtuple_t = typename std::tuple<typename std::tuple_element<Indices, Tuple>::type...>;
template <typename Tuple, unsigned... Indices>
constexpr subtuple_t<Tuple, Indices...> make_subtuple(const Tuple& tuple, sequence<Indices...>) {
return std::make_tuple(std::get<Indices>(tuple)...);
}
/*
* Factorial
*/
constexpr unsigned long long factorial(unsigned n) {
return n <= 1 ? 1 : n * factorial(n - 1);
}
/*
* e^n, where n is integer
*/
namespace { // anonymous namespace
constexpr double expi_nonnegative(unsigned n) {
return n == 0 ? 1.0 : (n == 1 ? 2.718281828459045 : expi_nonnegative(n / 2) * expi_nonnegative((n + 1) / 2));
}
} // anonymous namespace
constexpr double expi(int n) {
return (n >= 0 ? expi_nonnegative(n) : 1.0 / expi_nonnegative(-n));
}
}
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