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,
  20  * CA 94065 USA or visit www.oracle.com if you need additional information or
  21  * have any questions.
  22  *
  23  */
  24 
  25 package sun.jvm.hotspot.code;
  26 
  27 import 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 
  36 public 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 }