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

   1 /*
   2  * Svjatoslav Commons - shared library of common functionality.
   3  * Copyright ©2012-2020, 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 3 of the GNU Lesser General Public License
   7  * or later as published by the Free Software Foundation.
   8  */
   9
  10 package eu.svjatoslav.commons.data;
  11
  12
  13 import java.io.IOException;
  14 import java.io.InputStream;
  15
  16 /**
  17  * Read individual bits from the input stream.
  18  */
  19 public class BitInputStream {
  20
  21     private final InputStream inputStream;
  22     private int currentByte;
  23     private int currentBytePointer = -1;
  24
  25     public BitInputStream(final InputStream inputStream) {
  26         this.inputStream = inputStream;
  27     }
  28
  29     public int readBits(final int bitCount) throws IOException {
  30
  31         int readableByte = 0;
  32         for (int i = 0; i < bitCount; i++) {
  33
  34             readableByte = readableByte << 1;
  35
  36             if (currentBytePointer == -1) {
  37                 currentBytePointer = 7;
  38                 currentByte = inputStream.read();
  39             }
  40
  41             int mask = 1;
  42             mask = mask << currentBytePointer;
  43
  44             final int currentBit = currentByte & mask;
  45
  46             if (currentBit != 0)
  47                 readableByte = readableByte | 1;
  48
  49             currentBytePointer--;
  50         }
  51         return readableByte;
  52     }
  53
  54 }