ceph/src/boost/libs/hana/example/tutorial/integral.cpp

   1 // Copyright Louis Dionne 2013-2017
   2 // Distributed under the Boost Software License, Version 1.0.
   3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   4
   5 #include <boost/mpl/equal_to.hpp>
   6 #include <boost/mpl/int.hpp>
   7 #include <boost/mpl/integral_c.hpp>
   8 #include <boost/mpl/minus.hpp>
   9 #include <boost/mpl/multiplies.hpp>
  10 #include <boost/mpl/pair.hpp>
  11 #include <boost/mpl/plus.hpp>
  12
  13 #include <boost/hana/assert.hpp>
  14 #include <boost/hana/concept/constant.hpp>
  15 #include <boost/hana/equal.hpp>
  16 #include <boost/hana/integral_constant.hpp>
  17 #include <boost/hana/minus.hpp>
  18 #include <boost/hana/mult.hpp>
  19 #include <boost/hana/pair.hpp>
  20 #include <boost/hana/plus.hpp>
  21
  22 #include <type_traits>
  23 namespace hana = boost::hana;
  24
  25
  26 template <typename T, typename = std::enable_if_t<
  27   !hana::Constant<T>::value
  28 >>
  29 constexpr T sqrt(T x) {
  30   T inf = 0, sup = (x == 1 ? 1 : x/2);
  31   while (!((sup - inf) <= 1 || ((sup*sup <= x) && ((sup+1)*(sup+1) > x)))) {
  32     T mid = (inf + sup) / 2;
  33     bool take_inf = mid*mid > x ? 1 : 0;
  34     inf = take_inf ? inf : mid;
  35     sup = take_inf ? mid : sup;
  36   }
  37
  38   return sup*sup <= x ? sup : inf;
  39 }
  40
  41 template <typename T, typename = std::enable_if_t<
  42   hana::Constant<T>::value
  43 >>
  44 constexpr auto sqrt(T const&) {
  45   return hana::integral_c<typename T::value_type, sqrt(T::value)>;
  46 }
  47
  48
  49 namespace then {
  50 namespace mpl = boost::mpl;
  51
  52 template <typename N>
  53 struct sqrt
  54   : mpl::integral_c<typename N::value_type, ::sqrt(N::value)>
  55 { };
  56
  57 template <typename X, typename Y>
  58 struct point {
  59   using x = X;
  60   using y = Y;
  61 };
  62
  63 //! [distance-mpl]
  64 template <typename P1, typename P2>
  65 struct distance {
  66   using xs = typename mpl::minus<typename P1::x,
  67                                  typename P2::x>::type;
  68   using ys = typename mpl::minus<typename P1::y,
  69                                  typename P2::y>::type;
  70   using type = typename sqrt<
  71     typename mpl::plus<
  72       typename mpl::multiplies<xs, xs>::type,
  73       typename mpl::multiplies<ys, ys>::type
  74     >::type
  75   >::type;
  76 };
  77
  78 static_assert(mpl::equal_to<
  79   distance<point<mpl::int_<3>, mpl::int_<5>>,
  80            point<mpl::int_<7>, mpl::int_<2>>>::type,
  81   mpl::int_<5>
  82 >::value, "");
  83 //! [distance-mpl]
  84 }
  85
  86
  87 namespace now {
  88 namespace hana = boost::hana;
  89 using namespace hana::literals;
  90
  91 template <typename X, typename Y>
  92 struct _point {
  93   X x;
  94   Y y;
  95 };
  96 template <typename X, typename Y>
  97 constexpr _point<X, Y> point(X x, Y y) { return {x, y}; }
  98
  99 //! [distance-hana]
 100 template <typename P1, typename P2>
 101 constexpr auto distance(P1 p1, P2 p2) {
 102   auto xs = p1.x - p2.x;
 103   auto ys = p1.y - p2.y;
 104   return sqrt(xs*xs + ys*ys);
 105 }
 106
 107 BOOST_HANA_CONSTANT_CHECK(distance(point(3_c, 5_c), point(7_c, 2_c)) == 5_c);
 108 //! [distance-hana]
 109
 110 void test() {
 111
 112 //! [distance-dynamic]
 113 auto p1 = point(3, 5); // dynamic values now
 114 auto p2 = point(7, 2); //
 115 BOOST_HANA_RUNTIME_CHECK(distance(p1, p2) == 5); // same function works!
 116 //! [distance-dynamic]
 117
 118 }
 119 }
 120
 121
 122 int main() {
 123   now::test();
 124 }