1/*
2 * Copyright (c) 2000, 2005, 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.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25package sun.jvm.hotspot.code;
26
27import sun.jvm.hotspot.debugger.*;
28
29/** NOTE that this class takes the address of a buffer. This means
30    that it can read previously-generated debug information directly
31    from the target VM. However, it also means that you can't create a
32    "wrapper" object for a CompressedStream down in the VM. It looks
33    like these are only kept persistently in OopMaps, and the code has
34    been special-cased in OopMap.java to handle this. */
35
36public class CompressedStream {
37  protected Address buffer;
38  protected int     position;
39
40  /** Equivalent to CompressedStream(buffer, 0) */
41  public CompressedStream(Address buffer) {
42    this(buffer, 0);
43  }
44
45  public CompressedStream(Address buffer, int position) {
46    this.buffer   = buffer;
47    this.position = position;
48  }
49
50  public Address getBuffer() {
51    return buffer;
52  }
53
54  public static final int LogBitsPerByte = 3;
55  public static final int BitsPerByte = 1 << 3;
56
57  // Constants for UNSIGNED5 coding of Pack200
58  public static final int lg_H = 6;
59  public static final int H = 1<<lg_H;  // number of high codes (64)
60  public static final int L = (1<<BitsPerByte) - H; // number of low codes (192)
61  public static final int MAX_i = 4;      // bytes are numbered in (0..4)
62
63  // Positioning
64  public int getPosition() {
65    return position;
66  }
67  public void setPosition(int position) {
68    this.position = position;
69  }
70
71  // 32-bit one-to-one sign encoding taken from Pack200
72  // converts leading sign bits into leading zeros with trailing sign bit
73  public int encodeSign(int value) {
74    return (value << 1) ^ (value >> 31);
75  }
76
77  public int decodeSign(int value) {
78    return (value >>> 1) ^ -(value & 1);
79  }
80
81  // 32-bit self-inverse encoding of float bits
82  // converts trailing zeros (common in floats) to leading zeros
83  public int reverseInt(int i) {
84    // Hacker's Delight, Figure 7-1
85    i = (i & 0x55555555) << 1 | (i >>> 1) & 0x55555555;
86    i = (i & 0x33333333) << 3 | (i >>> 2) & 0x33333333;
87    i = (i & 0x0f0f0f0f) << 4 | (i >>> 4) & 0x0f0f0f0f;
88    i = (i << 24) | ((i & 0xff00) << 8) | ((i >>> 8) & 0xff00) | (i >>> 24);
89    return i;
90  }
91}
92