corrade-vassal – Rev 1
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/*
* CVS identifier:
*
* $Id: PktHeaderBitReader.java,v 1.10 2001/09/14 09:29:45 grosbois 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.
* */
using System;
using CSJ2K.j2k.io;
namespace CSJ2K.j2k.codestream.reader
{
/// <summary> This class provides a bit based reading facility from a byte based one,
/// applying the bit unstuffing procedure as required by the packet headers.
///
/// </summary>
//UPGRADE_NOTE: The access modifier for this class or class field has been changed in order to prevent compilation errors due to the visibility level. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1296'"
public class PktHeaderBitReader
{
/// <summary>The byte based source of data </summary>
internal RandomAccessIO in_Renamed;
/// <summary>The byte array that is the source of data if the PktHeaderBitReader
/// is instantiated with a buffer instead of a RandomAccessIO
/// </summary>
internal System.IO.MemoryStream bais;
/// <summary>Flag indicating whether the data should be read from the buffer </summary>
internal bool usebais;
/// <summary>The current bit buffer </summary>
internal int bbuf;
/// <summary>The position of the next bit to read in the bit buffer (0 means
/// empty, 8 full)
/// </summary>
internal int bpos;
/// <summary>The next bit buffer, if bit stuffing occurred (i.e. current bit
/// buffer holds 0xFF)
/// </summary>
internal int nextbbuf;
/// <summary> Instantiates a 'PktHeaderBitReader' that gets the byte data from the
/// given source.
///
/// </summary>
/// <param name="in">The source of byte data
///
/// </param>
internal PktHeaderBitReader(RandomAccessIO in_Renamed)
{
this.in_Renamed = in_Renamed;
usebais = false;
}
/// <summary> Instantiates a 'PktHeaderBitReader' that gets the byte data from the
/// given source.
///
/// </summary>
/// <param name="bais">The source of byte data
///
/// </param>
internal PktHeaderBitReader(System.IO.MemoryStream bais)
{
this.bais = bais;
usebais = true;
}
/// <summary> Reads a single bit from the input.
///
/// </summary>
/// <returns> The read bit (0 or 1)
///
/// </returns>
/// <exception cref="IOException">If an I/O error occurred
/// </exception>
/// <exception cref="EOFException">If teh end of file has been reached
///
/// </exception>
internal int readBit()
{
if (bpos == 0)
{
// Is bit buffer empty?
if (bbuf != 0xFF)
{
// No bit stuffing
if (usebais)
{
bbuf = bais.ReadByte();
}
else
{
bbuf = in_Renamed.read();
}
bpos = 8;
if (bbuf == 0xFF)
{
// If new bit stuffing get next byte
if (usebais)
{
nextbbuf = bais.ReadByte();
}
else
{
nextbbuf = in_Renamed.read();
}
}
}
else
{
// We had bit stuffing, nextbuf can not be 0xFF
bbuf = nextbbuf;
bpos = 7;
}
}
return (bbuf >> --bpos) & 0x01;
}
/// <summary> 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.
///
/// </summary>
/// <param name="n">The number of bits to read
///
/// </param>
/// <returns> The read bits, packed in the 'n' LSBs.
///
/// </returns>
/// <exception cref="IOException">If an I/O error occurred
/// </exception>
/// <exception cref="EOFException">If teh end of file has been reached
///
/// </exception>
internal int readBits(int n)
{
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.ReadByte();
}
else
{
bbuf = in_Renamed.read();
}
bpos = 8;
if (bbuf == 0xFF)
{
// If new bit stuffing get next byte
if (usebais)
{
nextbbuf = bais.ReadByte();
}
else
{
nextbbuf = in_Renamed.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;
}
}
/// <summary> 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.</p>
///
/// </summary>
internal virtual void sync()
{
bbuf = 0;
bpos = 0;
}
/// <summary> 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.</p>
///
/// </summary>
/// <param name="in">The source of byte data
///
/// </param>
internal virtual void setInput(RandomAccessIO in_Renamed)
{
this.in_Renamed = in_Renamed;
bbuf = 0;
bpos = 0;
}
/// <summary> 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.</p>
///
/// </summary>
/// <param name="bais">The source of byte data
///
/// </param>
internal virtual void setInput(System.IO.MemoryStream bais)
{
this.bais = bais;
bbuf = 0;
bpos = 0;
}
}
}
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