src/main/java/eu/svjatoslav/commons/data/BitInputStream.java

   1 /*
   2  * Svjatoslav Commons - shared library of common functionality.
   3  * Copyright (C) 2012, Svjatoslav Agejenko, svjatoslav@svjatoslav.eu
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of version 2 of the GNU General Public License
   7  * as published by the Free Software Foundation.
   8  */
   9
  10 package eu.svjatoslav.commons.data;
  11
  12 /**
  13  * Read individual bits from the input stream.
  14  */
  15
  16 import java.io.IOException;
  17 import java.io.InputStream;
  18
  19 public class BitInputStream {
  20
  21         int currentByte;
  22         int currentBytePointer = -1;
  23
  24         InputStream inputStream;
  25
  26         public BitInputStream(final InputStream inputStream) {
  27                 this.inputStream = inputStream;
  28         }
  29
  30         public int readBits(final int bitCount) throws IOException {
  31
  32                 int readableByte = 0;
  33                 for (int i = 0; i < bitCount; i++) {
  34
  35                         readableByte = readableByte << 1;
  36
  37                         if (currentBytePointer == -1) {
  38                                 currentBytePointer = 7;
  39                                 currentByte = inputStream.read();
  40                         }
  41
  42                         int mask = 1;
  43                         mask = mask << currentBytePointer;
  44
  45                         final int currentBit = currentByte & mask;
  46
  47                         if (currentBit != 0) {
  48                                 readableByte = readableByte | 1;
  49                         }
  50
  51                         currentBytePointer--;
  52                 }
  53                 return readableByte;
  54         }
  55
  56         public int readIntegerCompressed8() throws IOException {
  57                 if (readBits(1) == 0) {
  58                         return readBits(8);
  59                 } else {
  60                         return readBits(32);
  61                 }
  62         }
  63
  64 }