[fix] but primes behind an Arc

- don't clone primes for every thread, instead put it behind an Arc
  (atomic reference counted)
- print the pure calculation time at the end of the program
- don't show thread debug prints

src/main.rs

@@ -3,6 +3,7 @@ mod sieve;
 use std::{
     collections::HashMap,
     env,
+    sync::Arc,
     thread::{self, available_parallelism},
     time::Instant,
 };
@@ -76,7 +77,6 @@ fn calculate_chunk_bounds(i: usize, num_threads: usize, max_nr: usize) -> (usize
     let chunk_size = max_nr / num_threads;
     let start = i * chunk_size;
     let end = ((i + 1) * chunk_size).min(max_nr);
-    println!("Thread {i}: {start} - {end}");
     (start, end)
 }
 
@@ -92,10 +92,13 @@ fn main() {
     let primes = get_primes(MAX_SIEVED_PRIMES);
     println!("{} primes. Took {:?}", primes.len(), start.elapsed());
 
+    let primes = Arc::new(primes);
+
     #[allow(clippy::unwrap_used)]
     let num_threads = available_parallelism().unwrap().get();
     let mut threads = Vec::with_capacity(num_threads);
 
+    let now = Instant::now();
     for i in 0..num_threads {
         let (start, end) = calculate_chunk_bounds(i, num_threads, max_nr);
         let primes = primes.clone();
@@ -118,4 +121,6 @@ fn main() {
             max_teilers = teilers;
         }
     }
+
+    println!("Took {:?}", now.elapsed());
 }