math: introduce function to find gcd of 2 numbers

DIRECTORY.md

@@ -4,6 +4,7 @@
 - [Abs](math/abs.jule)
 - [Fact](math/fact.jule)
 - [Fib](math/fib.jule)
+- [Gcd](math/gcd.jule)
 - [Max](math/max.jule)
 - [Median](math/median.jule)
 - [Min](math/min.jule)

math/gcd.jule

@@ -0,0 +1,18 @@
+fn Gcd(a: int, b: int): int {
+	let mut x = a
+	let mut y = b
+
+	if x < 0 {
+		x = -x
+	}
+	if y < 0 {
+		y = -y
+	}
+
+	for y != 0 {
+		let t = x % y
+		x = y
+		y = t
+	}
+	return x
+}

math/gcd_test.jule

@@ -0,0 +1,14 @@
+#build test
+
+use "std/testing"
+
+#test
+fn testGcd(t: &testing::T) {
+	t.Assert(Gcd(54, 24) == 6, "gcd(54, 24) should be 6")
+	t.Assert(Gcd(48, 18) == 6, "gcd(48, 18) should be 6")
+	t.Assert(Gcd(17, 13) == 1, "gcd(17, 13) should be 1")
+	t.Assert(Gcd(0, 0) == 0, "gcd(0, 0) should be 0")
+	t.Assert(Gcd(0, 5) == 5, "gcd(0, 5) should be 5")
+	t.Assert(Gcd(-12, 18) == 6, "gcd(-12, 18) should be 6")
+	t.Assert(Gcd(12, -18) == 6, "gcd(12, -18) should be 6")
+}