2019: Port gcd to reusable library

Day 10 and, soon to be, Day 12 need the greatest common divisor.

2019/src/bin/puzzle_10.rs

@@ -3,21 +3,16 @@ use std::collections::HashMap;
 use std::io;
 
 use aoc2019::grid::Point;
+use aoc2019::num;
 
 #[derive(Ord, PartialOrd, Eq, PartialEq)]
 struct AsteroidMetadata {
     loc: Point,
     distance: u32,
 }
 
-fn gcd(mut a: i32, mut b: i32) -> i32 {
-    while b != 0 {
-        let t = b;
-        b = a % b;
-        a = t;
-    }
-
-    a.abs()
+fn gcd(a: i32, b: i32) -> i32 {
+    num::gcd(a.into(), b.into()).try_into().unwrap()
 }
 
 fn distances_from(

2019/src/lib.rs

@@ -1,3 +1,4 @@
 pub mod grid;
 pub mod intcode;
 pub mod iter;
+pub mod num;

2019/src/num.rs

@@ -0,0 +1,9 @@
+pub fn gcd(mut a: i64, mut b: i64) -> u64 {
+    while b != 0 {
+        let t = b;
+        b = a % b;
+        a = t;
+    }
+
+    a.abs().try_into().unwrap()
+}