jbig2_arith.c

/*
    jbig2dec

    Copyright (C) 2001-2005 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.
*/

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

#include <stdio.h>
#include <stdlib.h>

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

#ifdef JBIG2_DEBUG
#include <stdio.h>
#endif

struct _Jbig2ArithState {
  uint32_t C;
  int A;

  int CT;

  uint32_t next_word;
  int next_word_bytes;

  Jbig2WordStream *ws;
  int offset;
};

#undef SOFTWARE_CONVENTION

/*
  A note on the "software conventions".

  Previously, I had misinterpreted the spec, and had thought that the
  spec's description of the "software convention" was wrong. Now I
  believe that this code is both correct and matches the spec, with
  SOFTWARE_CONVENTION defined or not. Thanks to William Rucklidge for
  the clarification.

  In any case, my benchmarking indicates no speed difference at all.
  Therefore, for now we will just use the normative version.

 */

static void
jbig2_arith_bytein (Jbig2ArithState *as)
{
  byte B;

  /* invariant: as->next_word_bytes > 0 */

  /* Figure G.3 */
  B = (byte)((as->next_word >> 24) & 0xFF);
  if (B == 0xFF)
    {
      byte B1;
      if (as->next_word_bytes == 1)
	{
	  Jbig2WordStream *ws = as->ws;
	  as->next_word = ws->get_next_word (ws, as->offset);
	  as->offset += 4;
	  B1 = (byte)((as->next_word >> 24) & 0xFF);
	  if (B1 > 0x8F)
	    {
#ifdef JBIG2_DEBUG_ARITH
	      fprintf(stderr, "read %02x (aa)\n", B);
#endif
#ifndef SOFTWARE_CONVENTION
	      as->C += 0xFF00;
#endif
	      as->CT = 8;
	      as->next_word = (0xFF00 | B1) << 16;
	      as->next_word_bytes = 2;
	    }
	  else
	    {
#ifdef JBIG2_DEBUG_ARITH
	      fprintf(stderr, "read %02x (a)\n", B);
#endif
#ifdef SOFTWARE_CONVENTION
	      as->C += 0xFE00 - (B1 << 9);
#else
	      as->C += B1 << 9;
#endif
	      as->CT = 7;
	      as->next_word_bytes = 4;
	    }
	}
      else
	{
	  B1 = (byte)((as->next_word >> 16) & 0xFF);
	  if (B1 > 0x8F)
	    {
#ifdef JBIG2_DEBUG_ARITH
	      fprintf(stderr, "read %02x (ba)\n", B);
#endif
#ifndef SOFTWARE_CONVENTION
	      as->C += 0xFF00;
#endif
	      as->CT = 8;
	    }
	  else
	    {
	      as->next_word_bytes--;
	      as->next_word <<= 8;
#ifdef JBIG2_DEBUG_ARITH
	      fprintf(stderr, "read %02x (b)\n", B);
#endif

#ifdef SOFTWARE_CONVENTION
	      as->C += 0xFE00 - (B1 << 9);
#else
	      as->C += (B1 << 9);
#endif
	      as->CT = 7;
	    }
	}
    }
  else
    {
#ifdef JBIG2_DEBUG_ARITH
      fprintf(stderr, "read %02x\n", B);
#endif
      as->CT = 8;
      as->next_word <<= 8;
      as->next_word_bytes--;
      if (as->next_word_bytes == 0)
	{
	  Jbig2WordStream *ws = as->ws;

	  as->next_word = ws->get_next_word (ws, as->offset);
	  as->offset += 4;
	  as->next_word_bytes = 4;
	}
      B = (byte)((as->next_word >> 24) & 0xFF);
#ifdef SOFTWARE_CONVENTION
      as->C += 0xFF00 - (B << 8);
#else
      as->C += (B << 8);
#endif
    }
}

#if defined(JBIG2_DEBUG) || defined(JBIG2_DEBUG_ARITH)
#include <stdio.h>

static void
jbig2_arith_trace (Jbig2ArithState *as, Jbig2ArithCx cx)
{
  fprintf(stderr, "I = %2d, MPS = %d, A = %04x, CT = %2d, C = %08x\n",
	  cx & 0x7f, cx >> 7, as->A, as->CT, as->C);
}
#endif

/** Allocate and initialize a new arithmetic coding state
 *  the returned pointer can simply be freed; this does
 *  not affect the associated Jbig2WordStream.
 */
Jbig2ArithState *
jbig2_arith_new (Jbig2Ctx *ctx, Jbig2WordStream *ws)
{
  Jbig2ArithState *result;

  result = (Jbig2ArithState *)jbig2_alloc(ctx->allocator,
	sizeof(Jbig2ArithState));

  result->ws = ws;

  result->next_word = ws->get_next_word (ws, 0);
  result->next_word_bytes = 4;
  result->offset = 4;

  /* Figure G.1 */
#ifdef SOFTWARE_CONVENTION
  result->C = (~(result->next_word >> 8)) & 0xFF0000;
#else
  result->C = (result->next_word >> 8) & 0xFF0000;
#endif

  jbig2_arith_bytein (result);
  result->C <<= 7;
  result->CT -= 7;
  result->A = 0x8000;

  return result;
}

/* could put bit fields in to minimize memory usage */
typedef struct {
  unsigned short Qe;
  byte mps_xor; /* mps_xor = index ^ NMPS */
  byte lps_xor; /* lps_xor = index ^ NLPS ^ (SWITCH << 7) */
} Jbig2ArithQe;

const Jbig2ArithQe jbig2_arith_Qe[] = {
  { 0x5601,  1 ^  0,  1 ^  0 ^ 0x80 },
  { 0x3401,  2 ^  1,  6 ^  1 },
  { 0x1801,  3 ^  2,  9 ^  2 },
  { 0x0AC1,  4 ^  3, 12 ^  3 },
  { 0x0521,  5 ^  4, 29 ^  4 },
  { 0x0221, 38 ^  5, 33 ^  5 },
  { 0x5601,  7 ^  6,  6 ^  6 ^ 0x80 },
  { 0x5401,  8 ^  7, 14 ^  7 },
  { 0x4801,  9 ^  8, 14 ^  8 },
  { 0x3801, 10 ^  9, 14 ^  9 },
  { 0x3001, 11 ^ 10, 17 ^ 10 },
  { 0x2401, 12 ^ 11, 18 ^ 11 },
  { 0x1C01, 13 ^ 12, 20 ^ 12 },
  { 0x1601, 29 ^ 13, 21 ^ 13 },
  { 0x5601, 15 ^ 14, 14 ^ 14 ^ 0x80 },
  { 0x5401, 16 ^ 15, 14 ^ 15 },
  { 0x5101, 17 ^ 16, 15 ^ 16 },
  { 0x4801, 18 ^ 17, 16 ^ 17 },
  { 0x3801, 19 ^ 18, 17 ^ 18 },
  { 0x3401, 20 ^ 19, 18 ^ 19 },
  { 0x3001, 21 ^ 20, 19 ^ 20 },
  { 0x2801, 22 ^ 21, 19 ^ 21 },
  { 0x2401, 23 ^ 22, 20 ^ 22 },
  { 0x2201, 24 ^ 23, 21 ^ 23 },
  { 0x1C01, 25 ^ 24, 22 ^ 24 },
  { 0x1801, 26 ^ 25, 23 ^ 25 },
  { 0x1601, 27 ^ 26, 24 ^ 26 },
  { 0x1401, 28 ^ 27, 25 ^ 27 },
  { 0x1201, 29 ^ 28, 26 ^ 28 },
  { 0x1101, 30 ^ 29, 27 ^ 29 },
  { 0x0AC1, 31 ^ 30, 28 ^ 30 },
  { 0x09C1, 32 ^ 31, 29 ^ 31 },
  { 0x08A1, 33 ^ 32, 30 ^ 32 },
  { 0x0521, 34 ^ 33, 31 ^ 33 },
  { 0x0441, 35 ^ 34, 32 ^ 34 },
  { 0x02A1, 36 ^ 35, 33 ^ 35 },
  { 0x0221, 37 ^ 36, 34 ^ 36 },
  { 0x0141, 38 ^ 37, 35 ^ 37 },
  { 0x0111, 39 ^ 38, 36 ^ 38 },
  { 0x0085, 40 ^ 39, 37 ^ 39 },
  { 0x0049, 41 ^ 40, 38 ^ 40 },
  { 0x0025, 42 ^ 41, 39 ^ 41 },
  { 0x0015, 43 ^ 42, 40 ^ 42 },
  { 0x0009, 44 ^ 43, 41 ^ 43 },
  { 0x0005, 45 ^ 44, 42 ^ 44 },
  { 0x0001, 45 ^ 45, 43 ^ 45 },
  { 0x5601, 46 ^ 46, 46 ^ 46 }
};

static void
jbig2_arith_renormd (Jbig2ArithState *as)
{
  /* Figure E.18 */
  do
    {
      if (as->CT == 0)
	jbig2_arith_bytein (as);
      as->A <<= 1;
      as->C <<= 1;
      as->CT--;
    }
  while ((as->A & 0x8000) == 0);
}

bool
jbig2_arith_decode (Jbig2ArithState *as, Jbig2ArithCx *pcx)
{
  Jbig2ArithCx cx = *pcx;
  const Jbig2ArithQe *pqe = &jbig2_arith_Qe[cx & 0x7f];
  bool D;

  /* Figure G.2 */
  as->A -= pqe->Qe;
  if (
#ifdef SOFTWARE_CONVENTION
      /* Note: I do not think this is correct. See above. */
      (as->C >> 16) < as->A
#else
      !((as->C >> 16) < pqe->Qe)
#endif
      )
    {
#ifndef SOFTWARE_CONVENTION
      as->C -= pqe->Qe << 16;
#endif
      if ((as->A & 0x8000) == 0)
	{
	  /* MPS_EXCHANGE, Figure E.16 */
	  if (as->A < pqe->Qe)
	    {
	      D = 1 - (cx >> 7);
	      *pcx ^= pqe->lps_xor;
	    }
	  else
	    {
	      D = cx >> 7;
	      *pcx ^= pqe->mps_xor;
	    }
	  jbig2_arith_renormd (as);
	  return D;
	}
      else
	return cx >> 7;
    }
  else
    {
#ifdef SOFTWARE_CONVENTION
      as->C -= (as->A) << 16;
#endif
      /* LPS_EXCHANGE, Figure E.17 */
      if (as->A < pqe->Qe)
	{
	  as->A = pqe->Qe;
	  D = cx >> 7;
	  *pcx ^= pqe->mps_xor;
	}
      else
	{
	  as->A = pqe->Qe;
	  D = 1 - (cx >> 7);
	  *pcx ^= pqe->lps_xor;
	}
      jbig2_arith_renormd (as);
      return D;
    }
}

#ifdef TEST

static uint32_t
test_get_word (Jbig2WordStream *self, int offset)
{
  byte stream[] = {
    0x84, 0xC7, 0x3B, 0xFC, 0xE1, 0xA1, 0x43, 0x04, 0x02, 0x20, 0x00, 0x00,
    0x41, 0x0D, 0xBB, 0x86, 0xF4, 0x31, 0x7F, 0xFF, 0x88, 0xFF, 0x37, 0x47,
    0x1A, 0xDB, 0x6A, 0xDF, 0xFF, 0xAC,
    0x00, 0x00
  };
  if (offset >= sizeof(stream))
    return 0;
  else
    return (stream[offset] << 24) | (stream[offset + 1] << 16) |
      (stream[offset + 2] << 8) | stream[offset + 3];
}

int
main (int argc, char **argv)
{
  Jbig2Ctx *ctx;
  Jbig2WordStream ws;
  Jbig2ArithState *as;
  int i;
  Jbig2ArithCx cx = 0;

  ctx = jbig2_ctx_new(NULL, 0, NULL, NULL, NULL);

  ws.get_next_word = test_get_word;
  as = jbig2_arith_new (ctx, &ws);
#ifdef JBIG2_DEBUG_ARITH
  jbig2_arith_trace (as, cx);
#endif

  for (i = 0; i < 256; i++)
    {
      bool D;

      D = jbig2_arith_decode (as, &cx);
#ifdef JBIG2_DEBUG_ARITH
      fprintf(stderr, "%3d: D = %d, ", i, D);
      jbig2_arith_trace (as, cx);
#endif
    }

  jbig2_free(ctx->allocator, as);

  jbig2_ctx_free(ctx);

  return 0;
}
#endif