Fix bug and make testing more reliable

Cargo.toml

@@ -5,5 +5,3 @@ edition = "2021"
 
 [dependencies]
 
-[dev-dependencies]
-rayon = "1.10.0"

src/lib.rs

@@ -1,6 +1,7 @@
 /// It is not actually necissary or even recommended to use this code.
 /// The compiler should always optimize division with constant denominators for you.
 /// This code is just to help understand how the compilers optimization works.
+#[inline(always)]
 pub fn div10(num: u32) -> (u32, u32) {
     // Calculate num / 10
     // Note: 0.10 = 3435973837 / (1<<35)
@@ -9,7 +10,7 @@ pub fn div10(num: u32) -> (u32, u32) {
     // Calculate quot * 10
     // Note: 10x = 2x + 4(2x)
     let quot2 = quot << 1;
-    let quot8 = quot2 << 3;
+    let quot8 = quot2 << 2;
     let quot10 = quot2 + quot8;
 
     // Calculate the remainder
@@ -22,14 +23,12 @@ pub fn div10(num: u32) -> (u32, u32) {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use rayon::prelude::*;
 
     #[test]
-    /// This will take a REALLY long time
     fn brute_check() {
-        (0..=u32::MAX).into_par_iter().for_each(|i| {
+        for i in 0..=u32::MAX {
             let ans = (i / 10, i % 10);
             assert_eq!(ans, div10(i));
-        });
+        }
     }
 }