/*
    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 270 2003-07-16 00:40:34Z giles $
*/

#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
	      printf ("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
	      printf ("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
	      printf ("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
	      printf ("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
      printf ("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
    }
}

#ifdef JBIG2_DEBUG
#include <stdio.h>

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

Jbig2ArithState *
jbig2_arith_new (Jbig2Ctx *ctx, Jbig2WordStream *ws)
{
  Jbig2ArithState *result = (Jbig2ArithState *)malloc (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 int32_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)
{
  Jbig2WordStream ws;
  Jbig2ArithState *as;
  int i;
  Jbig2ArithCx cx = 0;

  ws.get_next_word = test_get_word;
  as = jbig2_arith_new (NULL, &ws);
  jbig2_arith_trace (as, cx);

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

      D = jbig2_arith_decode (as, &cx);
      printf ("%3d: D = %d, ", i, D);
      jbig2_arith_trace (as, cx);
      
    }
  return 0;
}
#endif
