1 package org.apache.lucene.util.collections;
3 import java.util.Arrays;
4 import java.util.Iterator;
7 * Licensed to the Apache Software Foundation (ASF) under one or more
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10 * The ASF licenses this file to You under the Apache License, Version 2.0
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24 * An Array-based hashtable which maps Objects of generic type
25 * T to primitive float values.<br>
26 * The hashtable is constructed with a given capacity, or 16 as a default. In
27 * case there's not enough room for new pairs, the hashtable grows. <br>
28 * Capacity is adjusted to a power of 2, and there are 2 * capacity entries for
31 * The pre allocated arrays (for keys, values) are at length of capacity + 1,
32 * when index 0 is used as 'Ground' or 'NULL'.<br>
34 * The arrays are allocated ahead of hash operations, and form an 'empty space'
35 * list, to which the key,value pair is allocated.
37 * @lucene.experimental
39 public class ObjectToFloatMap<K> {
42 * Implements an IntIterator which iterates over all the allocated indexes.
44 private final class IndexIterator implements IntIterator {
46 * The last used baseHashIndex. Needed for "jumping" from one hash entry
49 private int baseHashIndex = 0;
52 * The next not-yet-visited index.
54 private int index = 0;
57 * Index of the last visited pair. Used in {@link #remove()}.
59 private int lastIndex = 0;
62 * Create the Iterator, make <code>index</code> point to the "first"
63 * index which is not empty. If such does not exist (eg. the map is
64 * empty) it would be zero.
66 public IndexIterator() {
67 for (baseHashIndex = 0; baseHashIndex < baseHash.length; ++baseHashIndex) {
68 index = baseHash[baseHashIndex];
75 public boolean hasNext() {
80 // Save the last index visited
86 // if the next index points to the 'Ground' it means we're done with
87 // the current hash entry and we need to jump to the next one. This
88 // is done until all the hash entries had been visited.
89 while (index == 0 && ++baseHashIndex < baseHash.length) {
90 index = baseHash[baseHashIndex];
96 @SuppressWarnings("unchecked")
97 public void remove() {
98 ObjectToFloatMap.this.remove((K) keys[lastIndex]);
104 * Implements an IntIterator, used for iteration over the map's keys.
106 private final class KeyIterator implements Iterator<K> {
107 private IntIterator iterator = new IndexIterator();
111 public boolean hasNext() {
112 return iterator.hasNext();
115 @SuppressWarnings("unchecked")
117 return (K) keys[iterator.next()];
120 public void remove() {
126 * Implements an Iterator of a generic type T used for iteration over the
129 private final class ValueIterator implements FloatIterator {
130 private IntIterator iterator = new IndexIterator();
134 public boolean hasNext() {
135 return iterator.hasNext();
138 public float next() {
139 return values[iterator.next()];
142 public void remove() {
148 * Default capacity - in case no capacity was specified in the constructor
150 private static int defaultCapacity = 16;
153 * Holds the base hash entries. if the capacity is 2^N, than the base hash
154 * holds 2^(N+1). It can hold
159 * The current capacity of the map. Always 2^N and never less than 16. We
160 * never use the zero index. It is needed to improve performance and is also
163 private int capacity;
165 * All objects are being allocated at map creation. Those objects are "free"
166 * or empty. Whenever a new pair comes along, a pair is being "allocated" or
167 * taken from the free-linked list. as this is just a free list.
169 private int firstEmpty;
172 * hashFactor is always (2^(N+1)) - 1. Used for faster hashing.
174 private int hashFactor;
177 * This array holds the unique keys
182 * In case of collisions, we implement a double linked list of the colliding
183 * hash's with the following next[] and prev[]. Those are also used to store
191 * Number of currently objects in the map.
196 * This array holds the values
201 * Constructs a map with default capacity.
203 public ObjectToFloatMap() {
204 this(defaultCapacity);
208 * Constructs a map with given capacity. Capacity is adjusted to a native
209 * power of 2, with minimum of 16.
212 * minimum capacity for the map.
214 public ObjectToFloatMap(int capacity) {
216 // Minimum capacity is 16..
217 while (this.capacity < capacity) {
218 // Multiply by 2 as long as we're still under the requested capacity
222 // As mentioned, we use the first index (0) as 'Ground', so we need the
223 // length of the arrays to be one more than the capacity
224 int arrayLength = this.capacity + 1;
226 this.values = new float[arrayLength];
227 this.keys = new Object[arrayLength];
228 this.next = new int[arrayLength];
230 // Hash entries are twice as big as the capacity.
231 int baseHashSize = this.capacity << 1;
233 this.baseHash = new int[baseHashSize];
235 // The has factor is 2^M - 1 which is used as an "AND" hashing operator.
236 // {@link #calcBaseHash()}
237 this.hashFactor = baseHashSize - 1;
245 * Adds a pair to the map. Takes the first empty position from the
246 * empty-linked-list's head - {@link firstEmpty}.
248 * New pairs are always inserted to baseHash, and are followed by the old
252 * integer which maps the given Object
254 * element which is being mapped using the given key
256 private void prvt_put(K key, float e) {
257 // Hash entry to which the new pair would be inserted
258 int hashIndex = calcBaseHashIndex(key);
260 // 'Allocating' a pair from the "Empty" list.
261 int objectIndex = firstEmpty;
264 firstEmpty = next[firstEmpty];
265 values[objectIndex] = e;
266 keys[objectIndex] = key;
268 // Inserting the new pair as the first node in the specific hash entry
269 next[objectIndex] = baseHash[hashIndex];
270 baseHash[hashIndex] = objectIndex;
272 // Announcing a new pair was added!
277 * Calculating the baseHash index using the internal <code>hashFactor</code>.
281 protected int calcBaseHashIndex(K key) {
282 return key.hashCode() & hashFactor;
286 * Empties the map. Generates the "Empty" space list for later allocation.
288 public void clear() {
289 // Clears the hash entries
290 Arrays.fill(this.baseHash, 0);
295 values[0] = Float.NaN;
297 // Mark all array entries as empty. This is done with
298 // <code>firstEmpty</code> pointing to the first valid index (1 as 0 is
299 // used as 'Ground').
302 // And setting all the <code>next[i]</code> to point at
304 for (int i = 1; i < this.capacity;) {
308 // Surly, the last one should point to the 'Ground'.
309 next[this.capacity] = 0;
313 * Checks if a given key exists in the map.
316 * that is checked against the map data.
317 * @return true if the key exists in the map. false otherwise.
319 public boolean containsKey(K key) {
320 return find(key) != 0;
324 * Checks if the given object exists in the map.<br>
325 * This method iterates over the collection, trying to find an equal object.
328 * object that is checked against the map data.
329 * @return true if the object exists in the map (in .equals() meaning).
332 public boolean containsValue(float o) {
333 for (FloatIterator iterator = iterator(); iterator.hasNext();) {
334 if (o == iterator.next()) {
342 * Find the actual index of a given key.
345 * @return index of the key. zero if the key wasn't found.
347 protected int find(K key) {
348 // Calculate the hash entry.
349 int baseHashIndex = calcBaseHashIndex(key);
351 // Start from the hash entry.
352 int localIndex = baseHash[baseHashIndex];
354 // while the index does not point to the 'Ground'
355 while (localIndex != 0) {
356 // returns the index found in case of of a matching key.
357 if (keys[localIndex].equals(key)) {
361 // next the local index
362 localIndex = next[localIndex];
365 // If we got this far, it could only mean we did not find the key we
366 // were asked for. return 'Ground' index.
371 * Find the actual index of a given key with it's baseHashIndex.<br>
372 * Some methods use the baseHashIndex. If those call {@link #find()} there's
373 * no need to re-calculate that hash.
376 * @param baseHashIndex
377 * @return the index of the given key, or 0 as 'Ground' if the key wasn't
380 private int findForRemove(K key, int baseHashIndex) {
381 // Start from the hash entry.
383 int index = baseHash[baseHashIndex];
385 // while the index does not point to the 'Ground'
387 // returns the index found in case of of a matching key.
388 if (keys[index].equals(key)) {
392 // next the local index
397 // If we got this far, it could only mean we did not find the key we
398 // were asked for. return 'Ground' index.
404 * Returns the float mapped with the given key.
407 * object who's mapped float we're interested in.
408 * @return a float mapped by the given key. Float.NaN if the key wasn't found.
410 public float get(K key) {
411 return values[find(key)];
415 * Grows the map. Allocates a new map of double the capacity, and
416 * fast-insert the old key-value pairs.
418 @SuppressWarnings("unchecked")
419 protected void grow() {
420 ObjectToFloatMap<K> that = new ObjectToFloatMap<K>(
423 // Iterates fast over the collection. Any valid pair is put into the new
424 // map without checking for duplicates or if there's enough space for
426 for (IndexIterator iterator = new IndexIterator(); iterator.hasNext();) {
427 int index = iterator.next();
428 that.prvt_put((K) this.keys[index], this.values[index]);
431 // Copy that's data into this.
432 this.capacity = that.capacity;
433 this.size = that.size;
434 this.firstEmpty = that.firstEmpty;
435 this.values = that.values;
436 this.keys = that.keys;
437 this.next = that.next;
438 this.baseHash = that.baseHash;
439 this.hashFactor = that.hashFactor;
444 * @return true if the map is empty. false otherwise.
446 public boolean isEmpty() {
451 * Returns a new iterator for the mapped floats.
453 public FloatIterator iterator() {
454 return new ValueIterator();
457 /** Returns an iterator on the map keys. */
458 public Iterator<K> keyIterator() {
459 return new KeyIterator();
463 * Prints the baseHash array, used for debug purposes.
465 @SuppressWarnings("unused")
466 private void printBaseHash() {
467 for (int i = 0; i < this.baseHash.length; i++) {
468 System.out.println(i + ".\t" + baseHash[i]);
473 * Inserts the <key,value> pair into the map. If the key already exists,
474 * this method updates the mapped value to the given one, returning the old
477 * @return the old mapped value, or {@link Float#NaN} if the key didn't exist.
479 public float put(K key, float e) {
481 int index = find(key);
485 // Set new data and exit.
486 float old = values[index];
491 // Is there enough room for a new pair?
492 if (size == capacity) {
497 // Now that everything is set, the pair can be just put inside with no
505 * Removes a <key,value> pair from the map and returns the mapped value,
506 * or {@link Float#NaN} if the none existed.
508 * @param key used to find the value to remove
509 * @return the removed value or {@link Float#NaN} if none existed.
511 public float remove(K key) {
512 int baseHashIndex = calcBaseHashIndex(key);
513 int index = findForRemove(key, baseHashIndex);
515 // If it is the first in the collision list, we should promote its
516 // next colliding element.
518 baseHash[baseHashIndex] = next[index];
521 next[prev] = next[index];
522 next[index] = firstEmpty;
525 return values[index];
532 * @return number of pairs currently in the map
539 * Translates the mapped pairs' values into an array of Objects
541 * @return an object array of all the values currently in the map.
543 public float[] toArray() {
545 float[] array = new float[size];
547 // Iterates over the values, adding them to the array.
548 for (FloatIterator iterator = iterator(); iterator.hasNext();) {
549 array[++j] = iterator.next();
555 * Translates the mapped pairs' values into an array of T
558 * the array into which the elements of the list are to be
559 * stored, if it is big enough; otherwise, use as much space as it can.
561 * @return an array containing the elements of the list
564 public float[] toArray(float[] a) {
566 // Iterates over the values, adding them to the array.
567 for (FloatIterator iterator = iterator(); j < a.length
568 && iterator.hasNext(); ++j) {
569 a[j] = iterator.next();
579 public String toString() {
580 StringBuffer sb = new StringBuffer();
582 Iterator<K> keyIterator = keyIterator();
583 while (keyIterator.hasNext()) {
584 K key = keyIterator.next();
588 if (keyIterator.hasNext()) {
594 return sb.toString();
598 public int hashCode() {
599 return getClass().hashCode() ^ size();
602 @SuppressWarnings("unchecked")
604 public boolean equals(Object o) {
605 ObjectToFloatMap<K> that = (ObjectToFloatMap<K>)o;
606 if (that.size() != this.size()) {
610 Iterator<K> it = keyIterator();
611 while (it.hasNext()) {
613 float v1 = this.get(key);
614 float v2 = that.get(key);
615 if (Float.compare(v1, v2) != 0) {