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Java > Open Source Codes > com > ibm > icu > impl > CalendarCache


1 /*
2  *******************************************************************************
3  * Copyright (C) 1996-2004, International Business Machines Corporation and *
4  * others. All Rights Reserved. *
5  *******************************************************************************
6  */
7 package com.ibm.icu.impl;
8
9 /**
10  * @internal
11  */
12 public class CalendarCache
13 {
14     /**
15      * @internal
16      */
17     public CalendarCache() {
18         makeArrays(arraySize);
19     }
20     
21     private void makeArrays(int newSize) {
22         keys = new long[newSize];
23         values = new long[newSize];
24         
25         for (int i = 0; i < newSize; i++) {
26             values[i] = EMPTY;
27         }
28         arraySize = newSize;
29         threshold = (int)(arraySize * 0.75);
30         size = 0;
31     }
32     
33     /**
34      * @internal
35      */
36     public synchronized long get(long key) {
37         return values[findIndex(key)];
38     }
39     
40     /**
41      * @internal
42      */
43     public synchronized void put(long key, long value)
44     {
45         if (size >= threshold) {
46             rehash();
47         }
48         int index = findIndex(key);
49         
50         keys[index] = key;
51         values[index] = value;
52         size++;
53     }
54     
55     private final int findIndex(long key) {
56         int index = hash(key);
57         int delta = 0;
58         
59         while (values[index] != EMPTY && keys[index] != key)
60         {
61             if (delta == 0) {
62                 delta = hash2(key);
63             }
64             index = (index + delta) % arraySize;
65         }
66         return index;
67     }
68     
69     private void rehash()
70     {
71         int oldSize = arraySize;
72         long[] oldKeys = keys;
73         long[] oldValues = values;
74         
75         if (pIndex < primes.length - 1) {
76             arraySize = primes[++pIndex];
77         } else {
78             arraySize = arraySize * 2 + 1;
79         }
80         size = 0;
81         
82         makeArrays(arraySize);
83         for (int i = 0; i < oldSize; i++) {
84             if (oldValues[i] != EMPTY) {
85                 put(oldKeys[i], oldValues[i]);
86             }
87         }
88         oldKeys = oldValues = null; // Help out the garbage collector
89 }
90     
91     
92     /**
93      * Produce a uniformly-distributed hash value from an integer key.
94      * This is essentially a linear congruential random number generator
95      * that uses the key as its seed value.
96      */
97     private final int hash(long key)
98     {
99         int h = (int)((key * 15821 + 1) % arraySize);
100         if (h < 0) {
101             h += arraySize;
102         }
103         return h;
104     }
105     
106     private final int hash2(long key) {
107         return arraySize - 2 - (int)(key % (arraySize-2) );
108     }
109     
110     static private final int primes[] = { // 5, 17, 31, 47, // for testing
111 61, 127, 509, 1021, 2039, 4093, 8191, 16381, 32749, 65521,
112         131071, 262139,
113     };
114
115     private int pIndex = 0;
116     private int size = 0;
117     private int arraySize = primes[pIndex];
118     private int threshold = (arraySize * 3) / 4;
119     
120     private long[] keys = new long[arraySize];
121     private long[] values = new long[arraySize];
122
123     /**
124      * @internal
125      */
126     static public long EMPTY = Long.MIN_VALUE;
127 }
128
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