Constructor Detail

• MQDecoder

  public MQDecoder(ByteInputBuffer iStream,
                   int nrOfContexts,
                   int[] initStates)

  Instantiates a new MQ-decoder, with the specified number of contexts and initial states. The compressed bytestream is read from the 'iStream' object.

  Parameters:

  iStream - the stream that contains the coded bits

  nrOfContexts - The number of contexts used

  initStates - The initial state for each context. A reference is kept to this array to reinitialize the contexts whenever 'reset()' or 'resetCtxts()' is called.

Method Detail

• fastDecodeSymbols

  public final boolean fastDecodeSymbols(int[] bits,
                                         int ctxt,
                                         int n)

  Decodes 'n' symbols from the bit stream using the same context 'ctxt'. If possible the MQ-coder speedup mode will be used to speed up decoding. The speedup mode is used if Q (the LPS probability for 'ctxt' is low enough) and the A and C registers permit decoding several MPS symbols without renormalization.

  Speedup mode should be used when decoding long runs of MPS with high probability with the same context.

  This methiod will return the decoded symbols differently if speedup mode was used or not. If true is returned, then speedup mode was used and the 'n' decoded symbols are all the same and it is returned ain bits[0] only. If false is returned then speedup mode was not used, the decoded symbols are probably not all the same and they are returned in bits[0], bits[1], ... bits[n-1].

  Parameters:

  bits - The array where to put the decoded symbols. Must be of length 'n' or more.

  ctxt - The context to use in decoding the symbols.

  n - The number of symbols to decode.

  Returns:

  True if speedup mode was used, false if not. If speedup mode was used then all the decoded symbols are the same and its value is returned in 'bits[0]' only (not in bits[1], bits[2], etc.).

• decodeSymbols

  public final void decodeSymbols(int[] bits,
                                  int[] cX,
                                  int n)

  This function performs the arithmetic decoding. The function receives an array in which to put the decoded symbols and an array of contexts with which to decode them.

  Each context has a current MPS and an index describing what the current probability is for the LPS. Each bit is decoded and if the probability of the LPS exceeds .5, the MPS and LPS are switched.

  Parameters:

  bits - The array where to place the decoded symbols. It should be long enough to contain 'n' elements.

  cX - The context to use in decoding each symbol.

  n - The number of symbols to decode

• decodeSymbol

  public final int decodeSymbol(int context)

  Arithmetically decodes one symbol from the bit stream with the given context and returns its decoded value.

  Each context has a current MPS and an index describing what the current probability is for the LPS. Each bit is encoded and if the probability of the LPS exceeds .5, the MPS and LPS are switched.

  Parameters:

  context - The context to use in decoding the symbol

  Returns:

  The decoded symbol, 0 or 1.

• checkPredTerm

  public boolean checkPredTerm()

  Checks for past errors in the decoding process using the predictable error resilient termination. This works only if the encoder used the predictable error resilient MQ termination, otherwise it reports wrong results. If an error is detected it means that the MQ bit stream has been wrongly decoded or that the MQ terminated segment length is too long. If no errors are detected it does not necessarily mean that the MQ bit stream has been correctly decoded.

  Returns:

  True if errors are found, false otherwise.

• getNumCtxts

  public final int getNumCtxts()

  Returns the number of contexts in the arithmetic coder.

  Returns:

  The number of contexts

• resetCtxt

  public final void resetCtxt(int c)

  Resets a context to the original probability distribution.

  Parameters:

  c - The number of the context (it starts at 0).

• resetCtxts

  public final void resetCtxts()

  Resets a context to the original probability distribution. The original probability distribution depends on the actual implementation of the arithmetic coder or decoder.

  Parameters:

  c - The index of the context (it starts at 0).

• nextSegment

  public final void nextSegment(byte[] buf,
                                int off,
                                int len)

  Resets the MQ decoder to start a new segment. This is like recreating a new MQDecoder object with new input data.

  Parameters:

  buf - The byte array containing the MQ encoded data. If null the current byte array is assumed.

  off - The index of the first element in 'buf' to be decoded. If negative the byte just after the previous segment is assumed, only valid if 'buf' is null.

  len - The number of bytes in 'buf' to be decoded. Any subsequent bytes are taken to be 0xFF.

• getByteInputBuffer

  public ByteInputBuffer getByteInputBuffer()

  Returns the underlying 'ByteInputBuffer' from where the MQ coded input bytes are read.

  Returns:

  The underlying ByteInputBuffer.