ping_ping.cc
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	#include "print_size.hh"
	#include <chrono>
	#include <iomanip>
	#include <iostream>
	#include <mpi.h>
	#include <vector>

	void fill_buffer(std::vector<int> &buf, size_t size) {
	buf.resize(size);
	for (auto &v : buf) {
	v = 0;
	}
	}

	using clk = std::chrono::high_resolution_clock;
	using second = std::chrono::duration<double>;

	int main() {
	int prank, psize;
	const auto N{30};
	size_t REP{1000};

	MPI_Init(NULL, NULL);
	MPI_Comm_rank(MPI_COMM_WORLD, &prank);
	MPI_Comm_size(MPI_COMM_WORLD, &psize);

	std::vector<int> buf;
	auto partner = (prank + 1) % psize;

	for (size_t n = 0; n < N; n += 2) {
	auto size = 1 << n;
	fill_buffer(buf, size);

	auto t_start = clk::now();
	for (size_t repetition = 0; repetition < REP; ++repetition) {
	MPI_Send(buf.data(), buf.size(), MPI_INT, partner, 0, MPI_COMM_WORLD);
	MPI_Recv(buf.data(), buf.size(), MPI_INT, partner, 0, MPI_COMM_WORLD,
	MPI_STATUS_IGNORE);
	}
	auto time_s = (second{clk::now() - t_start}).count() / REP;

	if (prank == 0) {
	auto size_b = size * sizeof(int);
	std::cout << "PingPing"
	<< " size: " << std::setw(10) << printHuman(size_b, "B", 2)
	<< " time: " << std::setw(10) << printHuman(time_s, "s")
	<< " bandwidth: " << std::setw(10)
	<< printHuman(size_b / time_s, "B/s", 2) << std::endl;
	}
	if (size > 256)
	REP = 1;
	}

	MPI_Finalize();

	return 0;
	}