parallelize longest period finder

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 },
+        )
+}