JAL-2738 helper method for convolving mappings

diff --git a/src/jalview/util/MathUtils.java b/src/jalview/util/MathUtils.java
new file mode 100644 (file)
index 0000000..72d46a2
--- /dev/null
+++ b/src/jalview/util/MathUtils.java
@@ -0,0 +1,22 @@
+package jalview.util;
+
+public class MathUtils
+{
+
+  /**
+   * Returns the greatest common divisor of two integers
+   * 
+   * @param a
+   * @param b
+   * @return
+   */
+  public static int gcd(int a, int b)
+  {
+    if (b == 0)
+    {
+      return Math.abs(a);
+    }
+    return gcd(b, a % b);
+  }
+
+}

diff --git a/test/jalview/util/MathUtilsTest.java b/test/jalview/util/MathUtilsTest.java
new file mode 100644 (file)
index 0000000..fc84741
--- /dev/null
+++ b/test/jalview/util/MathUtilsTest.java
@@ -0,0 +1,26 @@
+package jalview.util;
+
+import static org.testng.Assert.assertEquals;
+
+import org.testng.annotations.Test;
+
+public class MathUtilsTest
+{
+  @Test
+  public void testGcd()
+  {
+    assertEquals(MathUtils.gcd(0, 0), 0);
+    assertEquals(MathUtils.gcd(0, 1), 1);
+    assertEquals(MathUtils.gcd(1, 0), 1);
+    assertEquals(MathUtils.gcd(1, 1), 1);
+    assertEquals(MathUtils.gcd(1, -1), 1);
+    assertEquals(MathUtils.gcd(-1, 1), 1);
+    assertEquals(MathUtils.gcd(2, 3), 1);
+    assertEquals(MathUtils.gcd(4, 2), 2);
+    assertEquals(MathUtils.gcd(2, 4), 2);
+    assertEquals(MathUtils.gcd(2, -4), 2);
+    assertEquals(MathUtils.gcd(-2, 4), 2);
+    assertEquals(MathUtils.gcd(-2, -4), 2);
+    assertEquals(MathUtils.gcd(2 * 3 * 5 * 7 * 11, 3 * 7 * 13 * 17), 3 * 7);
+  }
+}