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

   1 /*
   2  * Svjatoslav Commons - shared library of common functionality. Author: Svjatoslav Agejenko.
   3  * This project is released under Creative Commons Zero (CC0) license.
   4  */
   5 package eu.svjatoslav.commons.data;
   6
   7
   8 import java.io.IOException;
   9 import java.io.InputStream;
  10
  11 /**
  12  * Read individual bits from the input stream.
  13  */
  14 public class BitInputStream {
  15
  16     private final InputStream inputStream;
  17     private int currentByte;
  18     private int currentBytePointer = -1;
  19
  20     public BitInputStream(final InputStream inputStream) {
  21         this.inputStream = inputStream;
  22     }
  23
  24     public int readBits(final int bitCount) throws IOException {
  25
  26         int readableByte = 0;
  27         for (int i = 0; i < bitCount; i++) {
  28
  29             readableByte = readableByte << 1;
  30
  31             if (currentBytePointer == -1) {
  32                 currentBytePointer = 7;
  33                 currentByte = inputStream.read();
  34             }
  35
  36             int mask = 1;
  37             mask = mask << currentBytePointer;
  38
  39             final int currentBit = currentByte & mask;
  40
  41             if (currentBit != 0)
  42                 readableByte = readableByte | 1;
  43
  44             currentBytePointer--;
  45         }
  46         return readableByte;
  47     }
  48
  49 }