42 lines
1.1 KiB
C++
42 lines
1.1 KiB
C++
// Copyright Louis Dionne 2013-2017
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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#include <boost/hana/functional/fix.hpp>
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#include <boost/hana/assert.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/equal.hpp>
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#include <boost/hana/eval_if.hpp>
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#include <boost/hana/functional/always.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/minus.hpp>
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#include <boost/hana/mult.hpp>
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namespace hana = boost::hana;
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BOOST_HANA_CONSTEXPR_LAMBDA auto fact = hana::fix([](auto fact, auto n) {
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return hana::eval_if(hana::equal(n, hana::ullong_c<0>),
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hana::always(hana::ullong_c<1>),
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[=](auto _) { return hana::mult(n, fact(_(n) - hana::ullong_c<1>)); }
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);
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});
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constexpr unsigned long long reference(unsigned long long n)
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{ return n == 0 ? 1 : n * reference(n - 1); }
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template <int n>
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void test() {
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BOOST_HANA_CONSTANT_CHECK(hana::equal(
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fact(hana::ullong_c<n>),
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hana::ullong_c<reference(n)>
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));
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test<n - 1>();
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}
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template <> void test<-1>() { }
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int main() {
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test<15>();
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}
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