Optimize calculations and Remove File IO

src/main.rs

@@ -2,10 +2,7 @@ use may::go;
 use may::sync::mpmc::{channel, Sender};
 use num_cpus;
 use std::env;
-use std::fs::OpenOptions;
+use std::time::{Instant, Duration};
-use std::io::prelude::*;
-use std::io::BufWriter;
-use std::time::Instant;
 
 fn main() {
     may::config().set_workers(num_cpus::get());
@@ -19,13 +16,6 @@ fn main() {
     if &start % 2 == 0 {
         start += 1;
     }
-    let file = OpenOptions::new()
-        .write(true)
-        .append(true)
-        .create(true)
-        .open("primes.txt")
-        .unwrap();
-    let mut buffer = BufWriter::new(file);
     println!("Starting {} threads", num_threads);
     for i in 0u16..num_threads {
         let tx = tx.clone();
@@ -35,25 +25,17 @@ fn main() {
         println!("Started thread {}", i);
     }
     let time_start = Instant::now();
-    let mut prime_count = 0;
     let mut primes: Vec<u64> = vec![];
+    primes.push(2);
     // receives all prime numbers via the channel receiver.
     // The received prime numbers are stored in a vector
     loop {
-        let result = rx.recv();
+        let result = rx.recv_timeout(Duration::from_millis(10));
         match result {
             Err(_) => break,
             Ok(prime) => {
-                prime_count += 1;
                 primes.push(prime);
                 println!("\r{: <30}", prime);
-                print!(
-                    "{} Primes/s",
-                    prime_count as f64 / time_start.elapsed().as_secs_f64()
-                );
-                if let Err(e) = buffer.write(&format!("{}\n", prime).into_bytes()) {
-                    panic!(e);
-                }
             }
         }
     }
@@ -61,7 +43,9 @@ fn main() {
     for prime in primes {
         prime_sum += prime as u128;
     }
+    println!();
     println!("Prime Sum: {}", prime_sum);
+    println!("Solution took: {} ms", time_start.elapsed().as_millis())
 }
 
 /// Calculates primes and increases by incr with every iteration
@@ -71,13 +55,20 @@ fn get_primes(start: u64, incr: u64, stop_after: u64, tx: &Sender<u64>) {
     let mut num = start;
     while num < stop_after {
         let mut is_prime = true;
-        if (num < 3) | (&num % 2 == 0) {
+        if num == 2 {
+            tx.send(num).unwrap();
+            num += incr;
+            continue;
+        }
+        if (num < 2) | (num != 2 && num % 2 == 0) {
             num += incr;
             continue;
         }
-        for i in (3u64..&num / 2).step_by(2) {
+        let max = (num as f64).sqrt().ceil() as u64;
+        for i in (3u64..=max).step_by(2) {
             if num % i == 0 {
                 is_prime = false;
+                break;
             }
         }
         if is_prime {