1 // Copyright (C) 2016-2018 T. Zachary Laine
2 //
3 // Distributed under the Boost Software License, Version 1.0. (See
4 // accompanying file LICENSE_1_0.txt or copy at
5 // http://www.boost.org/LICENSE_1_0.txt)
6 #include <boost/yap/expression.hpp>
7
8
9 template<typename T>
10 using term = boost::yap::terminal<boost::yap::expression, T>;
11
12 namespace yap = boost::yap;
13 namespace bh = boost::hana;
14
15
16 namespace user {
17
18 struct number
19 {
20 double value;
21
operator +(number lhs,number rhs)22 friend number operator+(number lhs, number rhs)
23 {
24 return number{lhs.value + rhs.value};
25 }
26
operator *(number lhs,number rhs)27 friend number operator*(number lhs, number rhs)
28 {
29 return number{lhs.value * rhs.value};
30 }
31 };
32
33 // A more efficient fused multiply-add operation would normally go here.
naxpy(number a,number x,number y)34 number naxpy(number a, number x, number y)
35 {
36 return number{a.value * x.value + y.value};
37 }
38
39 // Transforms expressions of the form "a * x + y" to "naxpy(a, x, y)" via
40 // the implicit transform customiztion point.
41 template<typename Expr1, typename Expr2, typename Expr3>
transform_expression(yap::expression<yap::expr_kind::plus,bh::tuple<yap::expression<yap::expr_kind::multiplies,bh::tuple<Expr1,Expr2>>,Expr3>> const & expr)42 decltype(auto) transform_expression(yap::expression<
43 yap::expr_kind::plus,
44 bh::tuple<
45 yap::expression<
46 yap::expr_kind::multiplies,
47 bh::tuple<Expr1, Expr2>>,
48 Expr3>> const & expr)
49 {
50 return naxpy(
51 evaluate(expr.left().left()),
52 evaluate(expr.left().right()),
53 evaluate(expr.right()));
54 }
55 }
56
57 term<user::number> a{{1.0}};
58 term<user::number> x{{42.0}};
59 term<user::number> y{{3.0}};
60
61 user::number
62 eval_as_yap_expr(decltype((a * x + y) * (a * x + y) + (a * x + y)) & expr)
63 {
64 return yap::evaluate(expr);
65 }
66
67 user::number eval_as_yap_expr_4x(decltype(
68 (a * x + y) * (a * x + y) + (a * x + y) + (a * x + y) * (a * x + y) +
69 (a * x + y) + (a * x + y) * (a * x + y) + (a * x + y) +
70 (a * x + y) * (a * x + y) + (a * x + y)) & expr)
71 {
72 return yap::evaluate(expr);
73 }
74
eval_as_cpp_expr(user::number a,user::number x,user::number y)75 user::number eval_as_cpp_expr(user::number a, user::number x, user::number y)
76 {
77 return (a * x + y) * (a * x + y) + (a * x + y);
78 }
79
eval_as_cpp_expr_4x(user::number a,user::number x,user::number y)80 user::number eval_as_cpp_expr_4x(user::number a, user::number x, user::number y)
81 {
82 return (a * x + y) * (a * x + y) + (a * x + y) + (a * x + y) * (a * x + y) +
83 (a * x + y) + (a * x + y) * (a * x + y) + (a * x + y) +
84 (a * x + y) * (a * x + y) + (a * x + y);
85 }
86
87
main()88 int main()
89 {
90 auto expr = (a * x + y) * (a * x + y) + (a * x + y);
91 user::number result_1 = eval_as_yap_expr(expr);
92 user::number result_2 =
93 eval_as_cpp_expr(yap::value(a), yap::value(x), yap::value(y));
94
95 (void)result_1;
96 (void)result_2;
97
98 return 0;
99 }
100