bitinputstream.java

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package com.jr81.source.compression;

/*
 * BitInputStream.java
 *
 * Created on 05 Dec 2006
 */

import java.io.* ;

/**
 *
 * @author  Moshe Fresko
 * @course	Algorithmic Programming 1
 * @exercise	1
 */

public class BitInputStream extends FilterInputStream
{

    	/** Constructor creates a new instance of BitInputStream,
    	 	A decarotor to InputStream, via FilterInputStream */
	public BitInputStream(InputStream is)
		{ super(is) ; }


	class BitManager {
		// Buffer to keep max of 7 bits (one byte)
		private int[] buf = new int[8] ;
		// Counter showing the bit number we are reading now
		private int cnt = -1 ;
		// If we are at the end of the stream
		boolean atTheEnd()
			{ return ((buf[7]==1)&&(cnt<0)) ; }
		// Set the flag for the end of stream
		void setTheEnd()
			{ buf[7]=1; cnt=-1; }
		// No more buffer, means we need to read the next byte
		boolean noMoreBuffer()
			{ return cnt<0 ; }
		// set the buffer
		void setNext(int next)
			{ // put the bits of the byte into the array
				for (cnt=0; cnt<8; ++cnt) {
					buf[cnt] = next % 2 ;
					next /= 2 ;
				}
				// if this was the last byte
				if (buf[7]==1) {
					for (cnt=7;cnt>=0;cnt--)
						if (buf[cnt]==0)
							break ;
					cnt-- ;
				} else {
					cnt = 6 ;
				}
			}
		// get the next bit
		int getNext()
			{  return buf[cnt--] ; }
		// how many left
		int left()
			{ return cnt+1 ; }

	} ;
	BitManager bitManager = new BitManager() ;

	byte[] tempBuf = null ;
	int    tempBufPtr = 0 ;
	int		 tempBufLen = 0 ;
	private int readNextByte() throws IOException
		{ int val = -1 ;
			if (tempBufPtr==tempBufLen)
				val = super.read() ;
			else {
				byte b = tempBuf[tempBufPtr++] ;
				if ((b&0x80)>0)
					val = ((int)(b&0x7F))|0x80 ;
				else
					val = b ;
			}
			return val ;
		}
    	/** Reads a single bit from the included stream.
    		Returns either 1 or 0, and at the end of stream returns -1. */
	public int read() throws IOException {
			// If we are already at the end, return -1
		if (bitManager.atTheEnd())
			return -1 ;
			// If we are in the last bit, then refill the buffer
		if (bitManager.noMoreBuffer()) {
			int i = readNextByte() ;
			if (i<0)
				bitManager.setTheEnd() ;
			else
				bitManager.setNext(i) ;
			return read() ;
		}
			// Return the specific bit
		return bitManager.getNext() ;
	}

		/** Reads a list of bits given in the byte array as 0's and 1's*/
	public int read(byte[] arr) throws IOException
		{ return read(arr,0,arr.length) ; }

	public int read(byte[] arr, int off, int len) throws IOException
	{	int bytelen = ( (len-bitManager.left()) / 7 ) ;
		tempBuf = new byte[bytelen] ;
		tempBufLen = in.read(tempBuf) ;
		tempBufPtr = 0 ;
		for (int i=0;i<len;++i) {
			int next = read() ;
			if (next<0)
				return i ;
			arr[off+i]=(byte) next ;
		}
		return len ;
	}

	public static void main(String[] args)
	{
		if (args.length<2)
		{
			System.out.println("Usage: java BitInputStream FromFile ToFile") ;
			System.out.println("where 'FromFile' is a file to be open as a Bit Stream") ;
			System.out.println("and they are written as characters of '0's and '1's") ;
			System.out.println("every line having one char") ;
			System.exit(1) ;
		}
		try {
			InputStream is = new BitInputStream(new BufferedInputStream(new FileInputStream(args[0]))) ;
			PrintWriter os = new PrintWriter(new OutputStreamWriter(new FileOutputStream(args[1]))) ;
			int next ;
			while ((next=is.read())>=0)
				os.println(next) ;
			is.close() ;
			os.close() ;
		} catch (FileNotFoundException fnfe) {
			System.out.println(args[0]+" file cannot be opened") ;
			System.exit(1) ;
		} catch (IOException ioe) {
			System.out.println("Error in reading file "+args[0]+" or writing file "+args[1]) ;
			System.exit(1) ;
		}
	}
}