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Java > Open Source Codes > org > eclipse > swt > internal > image > TIFFRandomFileAccess


1 /*******************************************************************************
2  * Copyright (c) 2000, 2003 IBM Corporation and others.
3  * All rights reserved. This program and the accompanying materials
4  * are made available under the terms of the Eclipse Public License v1.0
5  * which accompanies this distribution, and is available at
6  * http://www.eclipse.org/legal/epl-v10.html
7  *
8  * Contributors:
9  * IBM Corporation - initial API and implementation
10  *******************************************************************************/
11 package org.eclipse.swt.internal.image;
12
13 import java.io.*;
14
15 final class TIFFRandomFileAccess {
16
17     LEDataInputStream inputStream;
18     int start, current, next;
19     byte[][] buffers;
20
21     static final int CHUNK_SIZE = 8192;
22     static final int LIST_SIZE = 128;
23
24 public TIFFRandomFileAccess(LEDataInputStream stream) {
25     inputStream = stream;
26     start = current = next = inputStream.getPosition();
27     buffers = new byte[LIST_SIZE][];
28 }
29
30 void seek(int pos) throws IOException {
31     if (pos == current) return;
32     if (pos < start) throw new IOException();
33     current = pos;
34     if (current > next) {
35         int n = current - next;
36         /* store required bytes */
37         int index = next / CHUNK_SIZE;
38         int offset = next % CHUNK_SIZE;
39         while (n > 0) {
40             if (index >= buffers.length) {
41                 byte[][] oldBuffers = buffers;
42                 buffers = new byte[Math.max(index + 1, oldBuffers.length + LIST_SIZE)][];
43                 System.arraycopy(oldBuffers, 0, buffers, 0, oldBuffers.length);
44             }
45             if (buffers[index] == null) buffers[index] = new byte[CHUNK_SIZE];
46             int cnt = inputStream.read(buffers[index], offset, Math.min(n, CHUNK_SIZE - offset));
47             n -= cnt;
48             next += cnt;
49             index++;
50             offset = 0;
51         }
52     }
53 }
54
55 void read(byte b[]) throws IOException {
56     int size = b.length;
57     int nCached = Math.min(size, next - current);
58     int nMissing = size - next + current;
59     int destNext = 0;
60     if (nCached > 0) {
61         /* Get cached bytes */
62         int index = current / CHUNK_SIZE;
63         int offset = current % CHUNK_SIZE;
64         while (nCached > 0) {
65             int cnt = Math.min(nCached, CHUNK_SIZE - offset);
66             System.arraycopy(buffers[index], offset, b, destNext, cnt);
67             nCached -= cnt;
68             destNext += cnt;
69             index++;
70             offset = 0;
71         }
72     }
73     if (nMissing > 0) {
74         /* Read required bytes */
75         int index = next / CHUNK_SIZE;
76         int offset = next % CHUNK_SIZE;
77         while (nMissing > 0) {
78             if (index >= buffers.length) {
79                 byte[][] oldBuffers = buffers;
80                 buffers = new byte[Math.max(index, oldBuffers.length + LIST_SIZE)][];
81                 System.arraycopy(oldBuffers, 0, buffers, 0, oldBuffers.length);
82             }
83             if (buffers[index] == null) buffers[index] = new byte[CHUNK_SIZE];
84             int cnt = inputStream.read(buffers[index], offset, Math.min(nMissing, CHUNK_SIZE - offset));
85             System.arraycopy(buffers[index], offset, b, destNext, cnt);
86             nMissing -= cnt;
87             next += cnt;
88             destNext += cnt;
89             index++;
90             offset = 0;
91         }
92     }
93     current += size;
94 }
95
96 }
97
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