gcd algorithm added

algorithms/number/gcd.go

@@ -0,0 +1,47 @@
+package gcd
+
+func gcd(x uint, y uint) uint {
+	
+	var shift uint = 0
+
+	if x == y {
+		return x
+	}
+
+	if x == 0 {
+		return y
+	}
+
+	if y == 0 {
+		return x
+	}
+
+	for shift := 0; (x | y) & 1 == 0; shift++ {
+		x = x >> 1
+		y = y >> 1
+	}
+
+	for ; (x & 1) == 0 ; {
+		x = x >> 1
+	}
+
+	for ; y == 0 ; {
+		
+		for ; (y & 1) == 0 ; {
+			y = y >> 1
+		}
+
+		if x > y {
+			t := x
+			x = y
+			y = t
+		}
+
+		y = y - x
+
+	}
+
+    y = y << shift
+
+	return y
+}

algorithms/number/gcd_test.go

@@ -0,0 +1,18 @@
+package gcd
+
+import "testing"
+
+func Test_gcd(t *testing.T) {
+
+	if gcd(100, 200) != 50 {
+		t.Error("[Error] gcd(100, 200) is wrong")
+	}
+
+	if gcd(4, 2) != 1 {
+		t.Error("[Error] gcd(4,2) is wrong")
+	}
+
+	if gcd(6, 3) != 3 {
+		t.Error("[Error] gcd(6,3) is wrong")
+	}
+}