Update gcd.js

algorithms/math/gcd.js

@@ -1,13 +1,27 @@
-// GCD - greatest common divisor or HCF - highest common factor
+"use strict";
 
-function gcd (small, large) {
-  if (small === 0) { return large } else { return gcd(large % small, small) }
-}
+/** @typedef {number|bigint} numeric */
 
-const gcdList = [[6, 9], [6, 12], [12, 18], [7, 14], [7, 13]]
+/** @param {numeric} x */
+const abs = x => x < 0 ? -x : x;
 
-for (const set of gcdList) {
-  const small = set[0]
-  const large = set[1]
-  console.log(`GCD for ${small} and ${large} is ${gcd(small, large)}`)
+/**
+ * GCD - greatest common divisor or HCF - highest common factor.
+ * Using the Euclidean algorithm (not to be confused with Euclid's algo, which does subtraction).
+ *
+ * Argument order doesn't matter.
+ * `return`s correct results even for non-integers (sometimes, because of rounding errors).
+ * This fn is 2-adic, the variadic implementation is left as an exercise to the reader.
+ * @param {numeric} a
+ * @param {numeric} b
+*/
+const gcd = (a, b) => {
+    while (b != 0)
+        [a, b] = [b, a % b];
+    return abs(a)
 }
+
+const tuples = [[6, 9], [6, 12], [-12, -18], [7, 14], [7, 13], [1/2, 2]];
+
+for (const [a, b] of tuples)
+    console.log(`GCD of ${a} and ${b} is ${gcd(a, b)}`);