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/*
* $RCSfile: PktHeaderBitReader.java,v $
* $Revision: 1.1 $
* $Date: 2005/02/11 05:02:01 $
* $State: Exp $
*
* Class: PktHeaderBitReader
*
* Description: Bit based reader for packet headers
*
*
*
* COPYRIGHT:
*
* This software module was originally developed by Raphaël Grosbois and
* Diego Santa Cruz (Swiss Federal Institute of Technology-EPFL); Joel
* Askelöf (Ericsson Radio Systems AB); and Bertrand Berthelot, David
* Bouchard, Félix Henry, Gerard Mozelle and Patrice Onno (Canon Research
* Centre France S.A) in the course of development of the JPEG2000
* standard as specified by ISO/IEC 15444 (JPEG 2000 Standard). This
* software module is an implementation of a part of the JPEG 2000
* Standard. Swiss Federal Institute of Technology-EPFL, Ericsson Radio
* Systems AB and Canon Research Centre France S.A (collectively JJ2000
* Partners) agree not to assert against ISO/IEC and users of the JPEG
* 2000 Standard (Users) any of their rights under the copyright, not
* including other intellectual property rights, for this software module
* with respect to the usage by ISO/IEC and Users of this software module
* or modifications thereof for use in hardware or software products
* claiming conformance to the JPEG 2000 Standard. Those intending to use
* this software module in hardware or software products are advised that
* their use may infringe existing patents. The original developers of
* this software module, JJ2000 Partners and ISO/IEC assume no liability
* for use of this software module or modifications thereof. No license
* or right to this software module is granted for non JPEG 2000 Standard
* conforming products. JJ2000 Partners have full right to use this
* software module for his/her own purpose, assign or donate this
* software module to any third party and to inhibit third parties from
* using this software module for non JPEG 2000 Standard conforming
* products. This copyright notice must be included in all copies or
* derivative works of this software module.
*
* Copyright (c) 1999/2000 JJ2000 Partners.
*
*
*
*/
package jj2000.j2k.codestream.reader;
import jj2000.j2k.io.*;
import java.io.*;
/**
* This class provides a bit based reading facility from a byte based one,
* applying the bit unstuffing procedure as required by the packet headers.
*
*/
class PktHeaderBitReader {
/** The byte based source of data */
RandomAccessIO in;
/** The byte array that is the source of data if the PktHeaderBitReader
* is instantiated with a buffer instead of a RandomAccessIO*/
ByteArrayInputStream bais;
/** Flag indicating whether the data should be read from the buffer */
boolean usebais;
/** The current bit buffer */
int bbuf;
/** The position of the next bit to read in the bit buffer (0 means
* empty, 8 full) */
int bpos;
/** The next bit buffer, if bit stuffing occurred (i.e. current bit
* buffer holds 0xFF) */
int nextbbuf;
/**
* Instantiates a 'PktHeaderBitReader' that gets the byte data from the
* given source.
*
* @param in The source of byte data
*
* */
PktHeaderBitReader(RandomAccessIO in) {
this.in = in;
usebais=false;
}
/**
* Instantiates a 'PktHeaderBitReader' that gets the byte data from the
* given source.
*
* @param bais The source of byte data
*
* */
PktHeaderBitReader(ByteArrayInputStream bais) {
this.bais = bais;
usebais=true;
}
/**
* Reads a single bit from the input.
*
* @return The read bit (0 or 1)
*
* @exception IOException If an I/O error occurred
*
* @exception EOFException If teh end of file has been reached
*
* */
final int readBit() throws IOException {
if (bpos == 0) { // Is bit buffer empty?
if (bbuf != 0xFF) { // No bit stuffing
if(usebais)
bbuf = bais.read();
else
bbuf = in.read();
bpos = 8;
if (bbuf == 0xFF) { // If new bit stuffing get next byte
if(usebais)
nextbbuf = bais.read();
else
nextbbuf = in.read();
}
}
else { // We had bit stuffing, nextbuf can not be 0xFF
bbuf = nextbbuf;
bpos = 7;
}
}
return (bbuf >> --bpos) & 0x01;
}
/**
* Reads a specified number of bits and returns them in a single
* integer. The bits are returned in the 'n' least significant bits of the
* returned integer. The maximum number of bits that can be read is 31.
*
* @param n The number of bits to read
*
* @return The read bits, packed in the 'n' LSBs.
* @exception IOException If an I/O error occurred
*
* @exception EOFException If teh end of file has been reached
*
* */
final int readBits(int n) throws IOException {
int bits; // The read bits
// Can we get all bits from the bit buffer?
if (n <= bpos) {
return (bbuf >> (bpos-=n)) & ((1<<n)-1);
}
else {
// NOTE: The implementation need not be recursive but the not
// recursive one exploits a bug in the IBM x86 JIT and caused
// incorrect decoding (Diego Santa Cruz).
bits = 0;
do {
// Get all the bits we can from the bit buffer
bits <<= bpos;
n -= bpos;
bits |= readBits(bpos);
// Get an extra bit to load next byte (here bpos is 0)
if (bbuf != 0xFF) { // No bit stuffing
if(usebais)
bbuf = bais.read();
else
bbuf = in.read();
bpos = 8;
if (bbuf == 0xFF) { // If new bit stuffing get next byte
if(usebais)
nextbbuf = bais.read();
else
nextbbuf = in.read();
}
}
else { // We had bit stuffing, nextbuf can not be 0xFF
bbuf = nextbbuf;
bpos = 7;
}
} while (n > bpos);
// Get the last bits, if any
bits <<= n;
bits |= (bbuf >> (bpos-=n)) & ((1<<n)-1);
// Return result
return bits;
}
}
/**
* Synchronizes this object with the underlying byte based input. It
* discards and buffered bits and gets ready to read bits from the current
* position in the underlying byte based input.
*
* <P>This method should always be called when some data has been read
* directly from the underlying byte based input since the last call to
* 'readBits()' or 'readBit()' before a new call to any of those methods.
*
* */
void sync() {
bbuf = 0;
bpos = 0;
}
/**
* Sets the underlying byte based input to the given object. This method
* discards any currently buffered bits and gets ready to start reading
* bits from 'in'.
*
* <P>This method is equivalent to creating a new 'PktHeaderBitReader'
* object.
*
* @param in The source of byte data
*
* */
void setInput(RandomAccessIO in) {
this.in = in;
bbuf = 0;
bpos = 0;
}
/**
* Sets the underlying byte based input to the given object. This method
* discards any currently buffered bits and gets ready to start reading
* bits from 'in'.
*
* <P>This method is equivalent to creating a new 'PktHeaderBitReader'
* object.
*
* @param bais The source of byte data
*
* */
void setInput(ByteArrayInputStream bais) {
this.bais = bais;
bbuf = 0;
bpos = 0;
}
}