matrices.c

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    */
   for (row = wfa->basis_states; row <= last_row; row++)
   {
      unsigned count;			/* value in the current interval */
      
      /*
       *  Read label 0 element
       */
      if (isrange (*is_leaf++))		/* valid matrix index */
      {
	 count = high - ((high - low) >> *prob_ptr);
	 if (code < count)
	 {
	    if (prob_ptr < last)	/* model update */
	       prob_ptr++;
	    /*
	     *  Decode the MPS '0'
	     */
	    high = count - 1;

	    RESCALE_INPUT_INTERVAL;
	 }
	 else
	 {
	    prob_ptr = ((prob_ptr - first) >> 1) + first; /* model update */
	    /*
	     *  Decode the LPS '1'
	     */
	    low = count;

	    RESCALE_INPUT_INTERVAL;
	    /*
	     *  Restore the transition (weight = -1)
	     */
	    append_edge (row, 0, -1, 0, wfa);
	    total++;
	 }
      }
      /*
       *  Read label 1 element
       */
      if (isrange (*is_leaf++)) /* valid matrix index */
      {
	 count = high - ((high - low) >> *prob_ptr);
	 if (code < count)
	 {
	    if (prob_ptr < last)
	       prob_ptr++;		/* model update */
	    /*
	     *  Decode the MPS '0'
	     */
	    high = count - 1;

	    RESCALE_INPUT_INTERVAL;
	 }
	 else
	 {
	    prob_ptr = ((prob_ptr - first) >> 1) + first; /* model update */
	    /*
	     *  Decode the LPS '1'
	     */
	    low = count;

	    RESCALE_INPUT_INTERVAL;
	    /*
	     *  Restore the transition (weight = -1)
	     */
	    append_edge (row, 0, -1, 1, wfa);
	    total++;
	 }
      }
   }

   INPUT_BYTE_ALIGN (input);

   Free (prob);
   
   return total;
}

static unsigned
chroma_decoding (wfa_t *wfa, bitfile_t *input)
/*
 *  Read transition matrices of 'wfa' states which are part of the
 *  chroma channels Cb and Cr from stream 'input'.
 *
 *  Return value:
 *	number of non-zero matrix elements (WFA edges)
 *
 *  Side effects:
 *	'wfa->into' is filled with decoded values 
 */
{
   unsigned  domain;			/* current domain, counter */
   unsigned  total = 0;			/* total number of chroma edges */
   unsigned *prob_ptr;			/* pointer to current probability */
   unsigned *last;			/* pointer to minimum probability */
   unsigned *first;			/* pointer to maximum probability */
   unsigned *new_prob_ptr;		/* ptr to probability of last domain */
   unsigned *prob;			/* probability array */
   u_word_t  high;			/* Start of the current code range */
   u_word_t  low;			/* End of the current code range */
   u_word_t  code;			/* The present input code value */
   word_t   *y_domains;			/* domain images corresponding to Y */
   int	     save_index;		/* YES: store current probabilty */

   /*
    *  Compute the asymmetric probability array
    *  prob[] = { 1/2, 1/2, 1/4, 1/4, 1/4, 1/4,
    *                     1/8, ... , 1/16, ..., 1/(MAXPROB+1)}
    */
   {
      unsigned n;
      unsigned index;			/* probability index */
      unsigned exp;			/* current exponent */
      
      prob = Calloc (1 << (MAX_PROB + 1), sizeof (unsigned));
   
      for (index = 0, n = MIN_PROB; n <= MAX_PROB; n++)
	 for (exp = 0; exp < 1U << n; exp++, index++)
	    prob [index] = n;
   }

   high = HIGH;				/* 1.0 */
   low  = LOW;				/* 0.0 */
   code = get_bits (input, 16);

   /*
    *  Compute list of admitted domains
    */
   y_domains = compute_hits (wfa->basis_states,
			     wfa->tree [wfa->tree [wfa->root_state][0]][0],
			     wfa->wfainfo->chroma_max_states, wfa);
   
   first = prob_ptr = new_prob_ptr = prob;
   last  = first + 1020;

   /*
    *  First of all, read all matrix columns given in the list 'y_domains'
    *  which note all admitted domains.
    *  These matrix elements are stored with QAC (see column_0_decoding ()).
    */
   for (domain = 0; y_domains [domain] != -1; domain++)
   {
      unsigned 	row	= wfa->tree [wfa->tree [wfa->root_state][0]][0] + 1;
      word_t   *is_leaf = wfa->tree [row];

      prob_ptr   = new_prob_ptr;
      save_index = YES;

      for (; row < wfa->states; row++)
      {
	 unsigned count;		/* value in the current interval */
	 /*
	  *  Read label 0 element
	  */
	 if (isrange (*is_leaf++)) 	/* valid matrix index */
	 {
	    count = high - ((high - low) >> *prob_ptr);
	    if (code < count)
	    {
	       if (prob_ptr < last)
		  prob_ptr++;
	       /*
		*  Decode the MPS '0'
		*/
	       high = count - 1;

	       RESCALE_INPUT_INTERVAL;
	    }
	    else
	    {
	       prob_ptr = ((prob_ptr - first) >> 1) + first;
	       /*
		*  Decode the LPS '1'
		*/
	       low = count;

	       RESCALE_INPUT_INTERVAL;
	       /*
		*  Restore the transition (weight = -1)
		*/
	       append_edge (row, y_domains [domain], -1, 0, wfa);
	       total++;
	    }
	 }
	 /*
	  *  Read label 1 element
	  */
	 if (isrange (*is_leaf++)) /* valid matrix index */
	 {
	    count = high - ((high - low) >> *prob_ptr);
	    if (code < count)
	    {
	       if (prob_ptr < last)
		  prob_ptr++;
	       /*
		*  Decode the MPS '0'
		*/
	       high = count - 1;

	       RESCALE_INPUT_INTERVAL;
	    }
	    else
	    {
	       prob_ptr = ((prob_ptr - first) >> 1) + first;
	       /*
		*  Decode the LPS '1'
		*/
	       low = count;

	       RESCALE_INPUT_INTERVAL;
	       /*
		*  Restore the transition (weight = -1)
		*/
	       append_edge (row, y_domains [domain], -1, 1, wfa);
	       total++;
	    }
	 }
	 if (save_index)
	 {
	    save_index 	 = NO;
	    new_prob_ptr = prob_ptr;
	 }
      }
   }

   Free (y_domains);

   compute_y_state (wfa->tree [wfa->tree [wfa->root_state][0]][1],
		    wfa->tree [wfa->tree [wfa->root_state][0]][0], wfa);
   compute_y_state (wfa->tree [wfa->tree [wfa->root_state][1]][0],
		    wfa->tree [wfa->tree [wfa->root_state][0]][0], wfa);
   
   first = prob_ptr = new_prob_ptr = prob;

   /*
    *  Decode the additional column which indicates whether there
    *  are transitions to a state with same spatial coordinates
    *  in the Y component.
    *
    *  Again, quasi arithmetic decoding is used for this task.
    */
   {
      unsigned 	row;
      
      for (row = wfa->tree [wfa->tree [wfa->root_state][0]][0] + 1;
	   row < wfa->states; row++)
      {
	 int label;			/* current label */

	 for (label = 0; label < MAXLABELS; label++)
	 {
	    u_word_t count = high - ((high - low) >> *prob_ptr);

	    if (code < count)
	    {
	       if (prob_ptr < last)
		  prob_ptr++;
	       /*
		*  Decode the MPS '0'
		*/
	       high = count - 1;

	       RESCALE_INPUT_INTERVAL;
	    }
	    else
	    {
	       prob_ptr = ((prob_ptr - first) >> 1) + first;
	       /*
		*  Decode the LPS '1'
		*/
	       low = count;

	       RESCALE_INPUT_INTERVAL;
	       /*
		*  Restore the transition (weight = -1)
		*/
	       append_edge (row, wfa->y_state [row][label], -1, label, wfa);
	       total++;
	    }
	 }
      }
   }

   INPUT_BYTE_ALIGN (input);

   Free (prob);

   return total;
}

static void
compute_y_state (int state, int y_state, wfa_t *wfa)
/*
 *  Compute the 'wfa->y_state' array which denotes those states of
 *  the Y band that have the same spatial coordinates as the corresponding
 *  states of the Cb and Cr bands.
 *  The current root of the Y tree is given by 'y_state'.
 *  The current root of the tree of the chroma channel is given by 'state'.
 *
 *  No return value.
 *
 *  Side effects:
 *	'wfa->y_state' is filled with the generated tree structure.
 */
{
   unsigned label;
   
   for (label = 0; label < MAXLABELS; label++)
      if (isrange (y_state))
	 wfa->y_state [state][label] = RANGE;
      else
      {
	 wfa->y_state [state][label] = wfa->tree [y_state][label];
	 if (!isrange (wfa->tree [state][label]))
	    compute_y_state (wfa->tree [state][label],
			     wfa->y_state [state][label], wfa);
      }
      
}