197 lines
6.5 KiB
C#
197 lines
6.5 KiB
C#
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/*
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* CVS identifier:
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*
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* $Id: ByteToBitInput.java,v 1.14 2002/07/19 12:41:33 grosbois Exp $
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*
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* Class: ByteToBitInput
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*
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* Description: Adapter to perform bit based input from a byte
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* based one.
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*
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*
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*
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* COPYRIGHT:
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*
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* This software module was originally developed by Rapha<EFBFBD>l Grosbois and
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* Diego Santa Cruz (Swiss Federal Institute of Technology-EPFL); Joel
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* Askel<EFBFBD>f (Ericsson Radio Systems AB); and Bertrand Berthelot, David
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* Bouchard, F<EFBFBD>lix Henry, Gerard Mozelle and Patrice Onno (Canon Research
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* Centre France S.A) in the course of development of the JPEG2000
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* standard as specified by ISO/IEC 15444 (JPEG 2000 Standard). This
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* software module is an implementation of a part of the JPEG 2000
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* Standard. Swiss Federal Institute of Technology-EPFL, Ericsson Radio
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* Systems AB and Canon Research Centre France S.A (collectively JJ2000
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* Partners) agree not to assert against ISO/IEC and users of the JPEG
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* 2000 Standard (Users) any of their rights under the copyright, not
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* including other intellectual property rights, for this software module
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* with respect to the usage by ISO/IEC and Users of this software module
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* or modifications thereof for use in hardware or software products
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* claiming conformance to the JPEG 2000 Standard. Those intending to use
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* this software module in hardware or software products are advised that
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* their use may infringe existing patents. The original developers of
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* this software module, JJ2000 Partners and ISO/IEC assume no liability
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* for use of this software module or modifications thereof. No license
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* or right to this software module is granted for non JPEG 2000 Standard
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* conforming products. JJ2000 Partners have full right to use this
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* software module for his/her own purpose, assign or donate this
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* software module to any third party and to inhibit third parties from
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* using this software module for non JPEG 2000 Standard conforming
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* products. This copyright notice must be included in all copies or
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* derivative works of this software module.
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*
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* Copyright (c) 1999/2000 JJ2000 Partners.
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* */
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using System;
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using CSJ2K.j2k.io;
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namespace CSJ2K.j2k.entropy.decoder
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{
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/// <summary> This class provides an adapter to perform bit based input on byte based
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/// output obejcts that inherit from a 'ByteInputBuffer' class. This class also
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/// performs the bit unstuffing procedure specified for the 'selective
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/// arithmetic coding bypass' mode of the JPEG 2000 entropy coder.
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///
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/// </summary>
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public class ByteToBitInput
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{
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/// <summary>The byte based input </summary>
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internal ByteInputBuffer in_Renamed;
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/// <summary>The bit buffer </summary>
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internal int bbuf;
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/// <summary>The position of the next bit to get from the byte buffer. When it is
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/// -1 the bit buffer is empty.
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/// </summary>
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internal int bpos = - 1;
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/// <summary> Instantiates a new 'ByteToBitInput' object that uses 'in' as the
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/// underlying byte based input.
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///
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/// </summary>
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/// <param name="in">The underlying byte based input.
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///
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/// </param>
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public ByteToBitInput(ByteInputBuffer in_Renamed)
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{
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this.in_Renamed = in_Renamed;
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}
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/// <summary> Reads from the bit stream one bit. If 'bpos' is -1 then a byte is read
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/// and loaded into the bit buffer, from where the bit is read. If
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/// necessary the bit unstuffing will be applied.
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///
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/// </summary>
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/// <returns> The read bit (0 or 1).
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///
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/// </returns>
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public int readBit()
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{
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if (bpos < 0)
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{
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if ((bbuf & 0xFF) != 0xFF)
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{
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// Normal byte to read
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bbuf = in_Renamed.read();
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bpos = 7;
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}
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else
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{
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// Previous byte is 0xFF => there was bit stuffing
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bbuf = in_Renamed.read();
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bpos = 6;
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}
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}
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return (bbuf >> bpos--) & 0x01;
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}
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/// <summary> Checks for past errors in the decoding process by verifying the byte
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/// padding with an alternating sequence of 0's and 1's. If an error is
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/// detected it means that the raw bit stream has been wrongly decoded or
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/// that the raw terminated segment length is too long. If no errors are
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/// detected it does not necessarily mean that the raw bit stream has been
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/// correctly decoded.
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///
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/// </summary>
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/// <returns> True if errors are found, false otherwise.
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///
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/// </returns>
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public virtual bool checkBytePadding()
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{
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int seq; // Byte padding sequence in last byte
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// If there are no spare bits and bbuf is 0xFF (not EOF), then there
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// is a next byte with bit stuffing that we must load.
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if (bpos < 0 && (bbuf & 0xFF) == 0xFF)
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{
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bbuf = in_Renamed.read();
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bpos = 6;
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}
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// 1) Not yet read bits in the last byte must be an alternating
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// sequence of 0s and 1s, starting with 0.
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if (bpos >= 0)
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{
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seq = bbuf & ((1 << (bpos + 1)) - 1);
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if (seq != (0x55 >> (7 - bpos)))
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return true;
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}
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// 2) We must have already reached the last byte in the terminated
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// segment, unless last bit read is LSB of FF in which case an encoder
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// can output an extra byte which is smaller than 0x80.
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if (bbuf != - 1)
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{
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if (bbuf == 0xFF && bpos == 0)
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{
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if ((in_Renamed.read() & 0xFF) >= 0x80)
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return true;
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}
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else
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{
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if (in_Renamed.read() != - 1)
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return true;
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}
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}
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// Nothing detected
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return false;
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}
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/// <summary> Flushes (i.e. empties) the bit buffer, without loading any new
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/// bytes. This realigns the input at the next byte boundary, if not
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/// already at one.
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///
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/// </summary>
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internal void flush()
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{
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bbuf = 0; // reset any bit stuffing state
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bpos = - 1;
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}
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/// <summary> Resets the underlying byte input to start a new segment. The bit buffer
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/// is flushed.
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///
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/// </summary>
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/// <param name="buf">The byte array containing the byte data. If null the
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/// current byte array is assumed.
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///
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/// </param>
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/// <param name="off">The index of the first element in 'buf' to be decoded. If
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/// negative the byte just after the previous segment is assumed, only
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/// valid if 'buf' is null.
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///
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/// </param>
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/// <param name="len">The number of bytes in 'buf' to be decoded. Any subsequent
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/// bytes are taken to be 0xFF.
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///
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/// </param>
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internal void setByteArray(byte[] buf, int off, int len)
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{
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in_Renamed.setByteArray(buf, off, len);
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bbuf = 0; // reset any bit stuffing state
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bpos = - 1;
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}
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}
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}
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