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Java > Open Source Codes > persistence > antlr > CharQueue


1 package persistence.antlr;
2
3 /* ANTLR Translator Generator
4  * Project led by Terence Parr at http://www.jGuru.com
5  * Software rights: http://www.antlr.org/license.html
6  *
7  */
8
9 /** A circular buffer object used by CharBuffer */
10 public class CharQueue {
11     /** Physical circular buffer of tokens */
12     protected char[] buffer;
13     /** buffer.length-1 for quick modulos */
14     private int sizeLessOne;
15     /** physical index of front token */
16     private int offset;
17     /** number of tokens in the queue */
18     protected int nbrEntries;
19
20     public CharQueue(int minSize) {
21         // Find first power of 2 >= to requested size
22 int size;
23         if ( minSize<0 ) {
24             init(16); // pick some value for them
25 return;
26         }
27         // check for overflow
28 if ( minSize>=(Integer.MAX_VALUE/2) ) {
29             init(Integer.MAX_VALUE); // wow that's big.
30 return;
31         }
32         for (size = 2; size < minSize; size *= 2) {
33         }
34         init(size);
35     }
36
37     /** Add token to end of the queue
38      * @param tok The token to add
39      */
40     public final void append(char tok) {
41         if (nbrEntries == buffer.length) {
42             expand();
43         }
44         buffer[(offset + nbrEntries) & sizeLessOne] = tok;
45         nbrEntries++;
46     }
47
48     /** Fetch a token from the queue by index
49      * @param idx The index of the token to fetch, where zero is the token at the front of the queue
50      */
51     public final char elementAt(int idx) {
52         return buffer[(offset + idx) & sizeLessOne];
53     }
54
55     /** Expand the token buffer by doubling its capacity */
56     private final void expand() {
57         char[] newBuffer = new char[buffer.length * 2];
58         // Copy the contents to the new buffer
59 // Note that this will store the first logical item in the
60 // first physical array element.
61 for (int i = 0; i < buffer.length; i++) {
62             newBuffer[i] = elementAt(i);
63         }
64         // Re-initialize with new contents, keep old nbrEntries
65 buffer = newBuffer;
66         sizeLessOne = buffer.length - 1;
67         offset = 0;
68     }
69
70     /** Initialize the queue.
71      * @param size The initial size of the queue
72      */
73     public void init(int size) {
74         // Allocate buffer
75 buffer = new char[size];
76         // Other initialization
77 sizeLessOne = size - 1;
78         offset = 0;
79         nbrEntries = 0;
80     }
81
82     /** Clear the queue. Leaving the previous buffer alone.
83      */
84     public final void reset() {
85         offset = 0;
86         nbrEntries = 0;
87     }
88
89     /** Remove char from front of queue */
90     public final void removeFirst() {
91         offset = (offset + 1) & sizeLessOne;
92         nbrEntries--;
93     }
94 }
95
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