108 lines
2.8 KiB
C++
108 lines
2.8 KiB
C++
// Copyright (C) 2016-2018 T. Zachary Laine
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#include <boost/yap/expression.hpp>
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template <typename T>
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using term = boost::yap::terminal<boost::yap::expression, T>;
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namespace yap = boost::yap;
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namespace bh = boost::hana;
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namespace user {
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struct number
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{
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double value;
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friend number operator+ (number lhs, number rhs)
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{ return number{lhs.value + rhs.value}; }
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friend number operator* (number lhs, number rhs)
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{ return number{lhs.value * rhs.value}; }
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};
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// A more efficient fused multiply-add operation would normally go here.
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number naxpy (number a, number x, number y)
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{ return number{a.value * x.value + y.value}; }
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// Transforms expressions of the form "a * x + y" to "naxpy(a, x, y)" via
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// the implicit transform customiztion point.
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template <typename Expr1, typename Expr2, typename Expr3>
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decltype(auto) transform_expression (
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yap::expression<
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yap::expr_kind::plus,
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bh::tuple<
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yap::expression<
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yap::expr_kind::multiplies,
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bh::tuple<
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Expr1,
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Expr2
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>
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>,
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Expr3
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>
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> const & expr
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) {
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return naxpy(
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evaluate(expr.left().left()),
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evaluate(expr.left().right()),
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evaluate(expr.right())
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);
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}
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}
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term<user::number> a{{1.0}};
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term<user::number> x{{42.0}};
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term<user::number> y{{3.0}};
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user::number eval_as_yap_expr (
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decltype((a * x + y) * (a * x + y) + (a * x + y)) & expr
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) {
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return yap::evaluate(expr);
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}
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user::number eval_as_yap_expr_4x (
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decltype(
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(a * x + y) * (a * x + y) + (a * x + y) +
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(a * x + y) * (a * x + y) + (a * x + y) +
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(a * x + y) * (a * x + y) + (a * x + y) +
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(a * x + y) * (a * x + y) + (a * x + y)
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) & expr
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) {
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return yap::evaluate(expr);
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}
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user::number eval_as_cpp_expr (user::number a, user::number x, user::number y)
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{
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return (a * x + y) * (a * x + y) + (a * x + y);
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}
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user::number eval_as_cpp_expr_4x (user::number a, user::number x, user::number y)
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{
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return
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(a * x + y) * (a * x + y) + (a * x + y) +
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(a * x + y) * (a * x + y) + (a * x + y) +
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(a * x + y) * (a * x + y) + (a * x + y) +
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(a * x + y) * (a * x + y) + (a * x + y);
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}
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int main ()
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{
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auto expr = (a * x + y) * (a * x + y) + (a * x + y);
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user::number result_1 = eval_as_yap_expr(expr);
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user::number result_2 =
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eval_as_cpp_expr(yap::value(a), yap::value(x), yap::value(y));
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(void)result_1;
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(void)result_2;
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return 0;
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}
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