1 /*
   2  * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.util.regex;
  27 
  28 import java.util.Arrays;
  29 
  30 /**
  31  * A lightweight hashset implementation for positive 'int'. Not safe for
  32  * concurrent access.
  33  */
  34 class IntHashSet {
  35     private int[] entries;
  36     private int[] hashes;
  37     private int pos = 0;
  38 
  39     public IntHashSet() {
  40         this.entries = new int[16 << 1];      // initCapacity = 16;
  41         this.hashes = new int[(16 / 2) | 1];  // odd -> fewer collisions
  42         Arrays.fill(this.entries, -1);
  43         Arrays.fill(this.hashes, -1);
  44     }
  45 
  46     public boolean contains(int i) {
  47         int h = hashes[i % hashes.length];
  48         while (h != -1) {
  49             if (entries[h] == i)
  50                 return true;
  51             h = entries[h + 1];
  52         }
  53         return false;
  54     }
  55 
  56     public void add(int i) {
  57         int h0 = i % hashes.length;
  58         int next = hashes[h0];
  59         //  if invoker guarantees contains(i) checked before add(i)
  60         //  the following check is not needed.
  61         int next0 = next;
  62         while (next0 != -1) {
  63             if (entries[next0 ] == i)
  64                 return;
  65             next0 = entries[next0 + 1];
  66         }
  67         hashes[h0] = pos;
  68         entries[pos++] = i;
  69         entries[pos++] = next;
  70         if (pos == entries.length)
  71             expand();
  72     }
  73 
  74     public void clear() {
  75         Arrays.fill(this.entries, -1);
  76         Arrays.fill(this.hashes, -1);
  77         pos = 0;
  78     }
  79 
  80     private void expand() {
  81         int[] old = entries;
  82         int[] es = new int[old.length << 1];
  83         int hlen = (old.length / 2) | 1;
  84         int[] hs = new int[hlen];
  85         Arrays.fill(es, -1);
  86         Arrays.fill(hs, -1);
  87         for (int n = 0; n < pos;) {  // re-hashing
  88             int i = old[n];
  89             int hsh = i % hlen;
  90             int next = hs[hsh];
  91             hs[hsh] = n;
  92             es[n++] = i;
  93             es[n++] = next;
  94         }
  95         this.entries = es;
  96         this.hashes = hs;
  97     }
  98 }