parallelize longest period finder

src/main.rs

@@ -3,7 +3,7 @@ mod period;
 mod tea3;
 
 use lfsr::Lfsr;
-use period::{longest_period, period_bruteforce, period_floyd, period_paper};
+use period::{longest_period_parallel, period_bruteforce, period_floyd, period_paper};
 use tea3::Tea3;
 
 fn main() {
@@ -65,7 +65,7 @@ fn main() {
     // println!("\nPaper period p20: {}", period_paper(vec![0x7a, 0x02, 0x00, 0x00, 0x00]));
     // println!("\nPaper period p27: {}", period_paper(vec![0x00, 0x00, 0x00, 0x00, 0x00]));
 
-    let (p, seed) = longest_period();
+    let (p, seed) = longest_period_parallel();
     println!("\nLongest period: {}", p);
     println!("Seed: {:02x?}", seed);
 }

src/period.rs

@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use rayon::prelude::*;
 
 use crate::tea3::Tea3;
 
@@ -177,3 +178,19 @@ pub fn longest_period() -> (u64, [u8; 5]) {
 
     (best_period, best_seed)
 }
+
+pub fn longest_period_parallel() -> (u64, [u8; 5]) {
+    let limit: usize = 1usize << 40;
+
+    (0usize..limit)
+        .into_par_iter()
+        .map(|x| {
+            let seed = Reg5::from_u40(x as u64);
+            let p = period_h(seed);
+            (p, seed.0)
+        })
+        .reduce(
+            || (0u64, [0u8; 5]),
+            |a, b| if a.0 >= b.0 { a } else { b },
+        )
+}