shithub: jbig2

ref: eb7f46063eb1b3e220c13839ef622c29bcf5834f
dir: /jbig2_arith_int.c/

/*
    jbig2dec
                                                                                
    Copyright (c) 2001 artofcode LLC.
                                                                                
    This software is provided AS-IS with no warranty,
    either express or implied.
                                                                                
    This software is distributed under license and may not
    be copied, modified or distributed except as expressly
    authorized under the terms of the license contained in
    the file LICENSE in this distribution.
                                                                                
    For information on commercial licensing, go to
    http://www.artifex.com/licensing/ or contact
    Artifex Software, Inc.,  101 Lucas Valley Road #110,
    San Rafael, CA  94903, U.S.A., +1(415)492-9861.
                                                                                
    $Id: jbig2_arith.c,v 1.13 2002/08/14 10:25:59 giles Exp $
*/

/* Annex A */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif 
#include "os_types.h"

#include <stddef.h>
#include <string.h> /* memset() */

#include "jbig2.h"
#include "jbig2_priv.h"
#include "jbig2_arith.h"
#include "jbig2_arith_int.h"

struct _Jbig2ArithIntCtx {
  Jbig2ArithCx IAx[512];
};

Jbig2ArithIntCtx *
jbig2_arith_int_ctx_new(Jbig2Ctx *ctx)
{
  Jbig2ArithIntCtx *result = jbig2_new(ctx, Jbig2ArithIntCtx, 1);

  memset(result->IAx, 0, sizeof(result->IAx));

  return result;
}

/* A.2 */
/* Return value: -1 on error, 0 on normal value, 1 on OOB return. */
int
jbig2_arith_int_decode(Jbig2ArithIntCtx *ctx, Jbig2ArithState *as,
		       int32_t *p_result)
{
  Jbig2ArithCx *IAx = ctx->IAx;
  int PREV = 1;
  int S, V;
  int bit;
  int n_tail, offset;
  int i;

  S = jbig2_arith_decode(as, &IAx[PREV]);
  PREV = (PREV << 1) | S;

  bit = jbig2_arith_decode(as, &IAx[PREV]);
  PREV = (PREV << 1) | bit;
  if (bit)
    {
      bit = jbig2_arith_decode(as, &IAx[PREV]);
      PREV = (PREV << 1) | bit;

      if (bit)
	{
	  bit = jbig2_arith_decode(as, &IAx[PREV]);
	  PREV = (PREV << 1) | bit;

	  if (bit)
	    {
	      bit = jbig2_arith_decode(as, &IAx[PREV]);
	      PREV = (PREV << 1) | bit;

	      if (bit)
		{
		  bit = jbig2_arith_decode(as, &IAx[PREV]);
		  PREV = (PREV << 1) | bit;

		  if (bit)
		    {
		      n_tail = 32;
		      offset = 4436;
		    }
		  else
		    {
		      n_tail = 12;
		      offset = 340;
		    }
		}
	      else
		{
		  n_tail = 8;
		  offset = 84;
		}
	    }
	  else
	    {
	      n_tail = 6;
	      offset = 20;
	    }
	}
      else
	{
	  n_tail = 4;
	  offset = 4;
	}
    }
  else
    {
      n_tail = 2;
      offset = 0;
    }

  V = 0;
  for (i = 0; i < n_tail; i++)
    {
      bit = jbig2_arith_decode(as, &IAx[PREV]);
      PREV = ((PREV << 1) & 511) | (PREV & 256) | bit;
      V = (V << 1) | bit;
    }

  V += offset;
  V = S ? -V : V;
  *p_result = V;
  return S && V == 0 ? 1 : 0;
}

void
jbig2_arith_int_ctx_free(Jbig2Ctx *ctx, Jbig2ArithIntCtx *iax)
{
  jbig2_free(ctx->allocator, iax);
}