Get yer integer to object mappings, cheap!

git-svn-id: https://samskivert.googlecode.com/svn/trunk@1051 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/util/CheapIntMap.java

@@ -0,0 +1,100 @@
+//
+// $Id: CheapIntMap.java,v 1.1 2003/02/06 19:57:29 mdb Exp $
+
+package com.samskivert.util;
+
+import java.util.Arrays;
+
+/**
+ * A low overhead hash map using positive integers as keys that is useful
+ * for fast storage and lookup of a small and bounded number of items.
+ */
+public class CheapIntMap
+{
+    /**
+     * Constructs a map that can hold the specified number of items.
+     */
+    public CheapIntMap (int maxSize)
+    {
+        _keys = new int[maxSize];
+        _values = new Object[maxSize];
+        clear();
+    }
+
+    /**
+     * Inserts the specified value into the map. <em>Note:</em> the key
+     * must be a positive integer.
+     */
+    public void put (int key, Object value)
+    {
+        int size = _keys.length, start = key % size, iidx = -1;
+        for (int ii = 0; ii < size; ii++) {
+            int idx = (ii + start) % size;
+            if (_keys[idx] == key) {
+                _values[idx] = value;
+                return;
+            } else if (iidx == -1 && _keys[idx] == -1) {
+                iidx = idx;
+            }
+        }
+
+        if (iidx != -1) {
+            _keys[iidx] = key;
+            _values[iidx] = value;
+            return;
+        }
+
+        // they booched it!
+        String errmsg = "You fool! You've filled up your cheap int map! " +
+            "[keys=" + StringUtil.toString(_keys) +
+            ", values=" + StringUtil.toString(_values) + "]";
+        throw new RuntimeException(errmsg);
+    }
+
+    /**
+     * Returns the object with the specified key, null if no object exists
+     * in the table with that key.
+     */
+    public Object get (int key)
+    {
+        int size = _keys.length, start = key % size;
+        for (int ii = 0; ii < size; ii++) {
+            int idx = (ii + start) % size;
+            if (_keys[idx] == key) {
+                return _values[idx];
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Removes the mapping associated with the specified key. The previous
+     * value of the mapping will be returned.
+     */
+    public Object remove (int key)
+    {
+        int size = _keys.length, start = key % size;
+        for (int ii = 0; ii < size; ii++) {
+            int idx = (ii + start) % size;
+            if (_keys[idx] == key) {
+                Object value = _values[idx];
+                _keys[idx] = -1;
+                _values[idx] = null;
+                return value;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Clears out all mappings from the table.
+     */
+    public void clear ()
+    {
+        Arrays.fill(_keys, -1);
+        Arrays.fill(_values, null);
+    }
+
+    protected int[] _keys;
+    protected Object[] _values;
+}

projects/samskivert/tests/src/java/com/samskivert/util/CheapIntMapTest.java

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+//
+// $Id: CheapIntMapTest.java,v 1.1 2003/02/06 19:57:29 mdb Exp $
+
+package com.samskivert.util;
+
+import junit.framework.Test;
+import junit.framework.TestCase;
+
+/**
+ * Tests the {@link CheapIntMap} class.
+ */
+public class CheapIntMapTest extends TestCase
+{
+    public CheapIntMapTest ()
+    {
+        super(CheapIntMapTest.class.getName());
+    }
+
+    public void runTest ()
+    {
+        CheapIntMap map = new CheapIntMap(10);
+
+        for (int ii = 0; ii < 100; ii += 20) {
+            map.put(ii, new Integer(ii));
+        }
+
+        for (int ii = 0; ii < 5; ii++) {
+            map.put(ii, new Integer(ii));
+        }
+
+        for (int ii = 0; ii < 100; ii++) {
+            Object val = map.get(ii);
+            if (val != null) {
+                System.out.println(ii + " => " + val);
+            }
+        }
+
+        for (int ii = 0; ii < 100; ii += 20) {
+            System.out.println("Removing " + map.remove(ii));
+        }
+
+        for (int ii = 10; ii > 0; ii--) {
+            map.put(ii, new Integer(ii));
+        }
+
+        for (int ii = 0; ii < 100; ii++) {
+            Object val = map.get(ii);
+            if (val != null) {
+                System.out.println(ii + " => " + val);
+            }
+        }
+    }
+
+    public static Test suite ()
+    {
+        return new CheapIntMapTest();
+    }
+
+    public static void main (String[] args)
+    {
+        CheapIntMapTest test = new CheapIntMapTest();
+        test.runTest();
+    }
+}