shithub: jbig2

ref: a43f448139d0a72688c9191adab0718b9ef43ec5
dir: /jbig2_arith_int.c/

/*
    jbig2dec

    Copyright (C) 2001 Artifex Software, Inc.

    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 further licensing information refer to http://artifex.com/ or
    contact Artifex Software, Inc., 7 Mt. Lassen Drive - Suite A-134,
    San Rafael, CA  94903, U.S.A., +1(415)492-9861.
*/

/* 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);

  if (result == NULL)
  {
      jbig2_error(ctx, JBIG2_SEVERITY_FATAL, -1,
          "failed to allocate Jbig2ArithIntCtx in jbig2_arith_int_ctx_new");
  }
  else
  {
      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);
}