Added Bankers (failing tests)

java/src/au/com/phiware/math/bankers/Bankers.java

@@ -0,0 +1,46 @@
+/**
+ * 
+ */
+package au.com.phiware.math.bankers;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import au.com.phiware.math.ring.BigIntegerArithmetic;
+import au.com.phiware.math.ring.BitArithmetic;
+import au.com.phiware.math.ring.IntegerArithmetic;
+import au.com.phiware.math.ring.LongArithmetic;
+
+/**
+ * @author Corin Lawson <me@corinlawson.com.au>
+ *
+ */
+public class Bankers {
+	private BitArithmetic<? extends Number> arithmetic;
+	private int length;
+
+	private Bankers(int length) {
+		if (length <= 32)
+			arithmetic = IntegerArithmetic.getInstance();
+		else if (length <= 64)
+			arithmetic = LongArithmetic.getInstance();
+		else
+			arithmetic = BigIntegerArithmetic.getInstance();
+		this.length = length;
+	}
+
+	public int length() {
+		return length;
+	}
+
+	private static Map<Integer, Bankers> instances = new HashMap<Integer, Bankers>();
+	public static Bankers getBanker(int length) {
+		if (!instances.containsKey(length))
+			instances.put(length, new Bankers(length));
+		return instances.get(length);
+	}
+
+	public <V extends Number> V next(V b) {
+		return null;
+	}
+}

java/test/au/com/phiware/math/bankers/BankersTest.java

@@ -0,0 +1,56 @@
+/**
+ * 
+ */
+package au.com.phiware.math.bankers;
+
+import static org.junit.Assert.*;
+
+import java.util.BitSet;
+
+import org.junit.Test;
+
+/**
+ * @author Corin Lawson <me@corinlawson.com.au>
+ *
+ */
+public class BankersTest {
+
+	public void testMonotonicity(Bankers bankers) {
+		int b = 0;
+		int c = 0;
+		for (int i = 0; i < 1 << bankers.length(); i++) {
+			b = bankers.next(b);
+			assertTrue(b+" at "+i+" should have no less than "+c+" ones", Integer.bitCount(b) >= c);
+			c = Integer.bitCount(b);
+		}
+	}
+
+	/**
+	 * The number of ones in the Banker's sequence should never decrease. 
+	 */
+	@Test
+	public void testMonotonicityUpTo10() {
+		for (int n = 2; n <= 10; n++)
+			testMonotonicity(Bankers.getBanker(n));
+	}
+
+	public void testIsomorphism(Bankers bankers) {
+		int b = 0;
+		BitSet seen = new BitSet(1 << bankers.length());
+		for (int i = 0; i < 1 << bankers.length(); i++) {
+			b = bankers.next(b);
+			assertFalse(b+" at "+i+" should not have been seen", seen.get(b));
+			seen.set(b);
+		}
+	}
+
+	/**
+	 * The natural numbers should have a one-to-one mapping to the Banker's numbers. 
+	 */
+	@Test
+	public void testIsomorphismUpTo10() {
+		for (int n = 2; n <= 10; n++)
+			testIsomorphism(Bankers.getBanker(n));
+	}
+
+}