//
//  main.cpp
//  Lab04_ulam
//
//  Created by Paweł Kalicki on 08/04/2020.
//  Copyright © 2020 Paweł Kalicki. All rights reserved.
//

#include <iostream>
#include <stdio.h>
#include <math.h>
#include <thread>
#include <vector>
#include <chrono>

#define thread_num 4
#define N 2048

using namespace std;

static unsigned char color [N][N][3];

chrono::duration<double> elapsed_seconds;

int ulam_get_map(int x, int y, int n)
{
    x -= (n - 1) / 2;
    y -= n / 2;

    int mx = abs(x), my = abs(y);
    int l = 2 * max(mx, my);
    int d = y >= x ? l * 3 + x + y : l - x - y;

    return pow(l - 1, 2) + d;
}

int isprime(int n)
{
    int p;

    for (p = 2; p*p <= n; p++)
        if (n%p == 0) return 0;

    return n > 2;
}

int main() {
    FILE * fp;
    char const *filename="ulam.ppm";
    char const *comment="# ";

    int i, start_width, stop_width, start_height, stop_height;

    vector<thread> workers;

    for (i=0; i < thread_num; i++)
    {
        start_width = (i%2)*N/(thread_num/2);
        stop_width = start_width + N/2;
        start_height = floor(i/2)*N/(thread_num/2);
        stop_height = start_height + N/2;

        workers.push_back(thread([start_width, stop_width, start_height, stop_height]()
        {
            chrono::system_clock::time_point start = chrono::system_clock::now();
            int i,j,k;
            for (j=start_width; j<stop_width; j++)
                for(k=start_height; k<stop_height; k++)
                    if (isprime(N*N - ulam_get_map(k,j, N)))
                        for (i=0;i<3;i++)
                            color[j][k][i] = 255;
            chrono::system_clock::time_point end = chrono::system_clock::now();
            elapsed_seconds += end - start;
        }));
    }

    for_each(workers.begin(), workers.end(), [](thread &t)
    {
        t.join();
    });

    fp = fopen(filename,"wb");
    fprintf(fp,"P6\n %s\n %d\n %d\n %d\n",comment,N,N,255);
    fwrite(color,1,3*N*N,fp);
    fclose(fp);

    cout << "elapsed time ulama's spiral: " << elapsed_seconds.count() << '\n';

    return 0;
}