diff --git a/src/lib.rs b/src/lib.rs
index 853ed1c..6dc7bc7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -342,6 +342,12 @@ struct Agent {
     goal: Solution,
 }
 
+macro_rules! rnd {
+    ($max: expr) => {
+        rand::random::<usize>() % $max
+    };
+}
+
 impl Agent {
     const WIN_REWARD: f32 = 100000.0;
     const BOX_REWARD: f32 = 0.00021;
@@ -354,7 +360,7 @@ impl Agent {
         &[Direction::U, Direction::D, Direction::L, Direction::R];
 
     fn chromo() -> Direction {
-        Self::DIR_TABLE[rand::random::<usize>() % Self::DIR_TABLE.len()]
+        Self::DIR_TABLE[rnd!(Self::DIR_TABLE.len())]
     }
 
     fn with_dna(state: State, dna: Vec<Direction>) -> Self {
@@ -374,7 +380,7 @@ impl Agent {
     }
 
     fn cross(&mut self, seed: &Self, cr: usize) {
-        let ratio = (rand::random::<usize>() % cr) + 1;
+        let ratio = rnd!(cr) + 1;
         let len = self.dna.len();
 
         self.dna[..len / ratio].copy_from_slice(&seed.dna[..len / ratio]);
@@ -382,8 +388,7 @@ impl Agent {
 
     fn mutate(&mut self, max: usize) {
         let len = self.dna.len();
-        let ni = rand::random::<usize>() % max;
-        let nd = rand::random::<usize>() % len;
+        let (ni, nd) = (rnd!(max), rnd!(len));
 
         for x in 0..ni {
             self.dna[(nd + x) % len] = Agent::chromo();