coroutine_fib.cpp

/*
-------------------------------------------------------------------------------
Best matrial(I think) currently: 
https://luncliff.github.io/coroutine/ppt/%5BEng%5DExploringTheCppCoroutine.pdf
= [Donald Knuth] Coroutines are functions that can suspend and resume their \
  execution while keeping their state.
= The coroutine in C++ 20 standard are stackless.
-------------------------------------------------------------------------------
= Key concepts:
>>> [Routine]: An ordered group of instrutions. [instr0 -> instr1 -> ...]

>>> A @ [Invocation]: Start of a routine. (say, `call`)
>>> B @ [Activation]: Jump into some point of the routine. (say instr1)
>>> C @ [Suspension]: Jump to another routine's point without finalization.
>>> D @ [Finalization]: Finished the routine. (say, `return`)

>>> A routine has 4 operands:
	 Invoke/Finalize/Suspend/Resume

>>> [[Subroutine]]: A routine that supports Invoke/Finalize. (Suspend/Resume not supported)

>>> [Process]: A set of routines.
>>> [Thread]: The abstraction of a control flow in a process. (e.g. 1 CPU core)

>>> [[Coroutine]]: supports all 4 operands.
-------------------------------------------------------------------------------
*/

#include <experimental/coroutine>
#include <experimental/generator>
#include <experimental/resumable>
#include <utility>
#include <iostream>
#include <chrono>
#include <vector>

using namespace std;
using namespace std::experimental;

generator<size_t> co_fibonacci(size_t n) {
	size_t a = 0, b = 1;
	while (n-- > 0) {
		co_yield a += b;
		swap(a, b);
	}
}

vector<size_t> normal_fibonacci(size_t n) {
	vector<size_t> ret{};
	ret.reserve(n);
	size_t a = 0, b = 1;
	while (n-- > 0) {
		ret.push_back(a += b);
		swap(a, b);
	}
	return ret;
}

template <typename I> generator<I> range(I r) { for (I i = 0; i < r; ++i) co_yield i; }

int main() {
	using clk_t = chrono::high_resolution_clock;
	constexpr size_t size = 300;

	auto bench = [size](auto&& callback, string_view name) {
		auto begin = clk_t::now();
		for (auto v : callback(size)) cout << v << ' ';
		cout << '\n' << chrono::duration<double, milli>(clk_t::now() - begin).count() << " ms for " << name << endl;
	};

	for (auto _ : range(10)) {
		bench(normal_fibonacci, "normal");
		bench(co_fibonacci, "coroutine");
	}
	
	cin.get();
}