FFmpeg/libavcodec/svq1.c

/*
 * 
 * Copyright (C) 2002 the xine project
 * Copyright (C) 2002 the ffmpeg project
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Ported to mplayer by Arpi <arpi@thot.banki.hu>
 * Ported to libavcodec by Nick Kurshev <nickols_k@mail.ru>
 *
 */

/**
 * @file svq1.c
 * Sorenson Vector Quantizer #1 (SVQ1) video decoder.
 */


//#define DEBUG_SVQ1
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "common.h"
#include "avcodec.h"
#include "dsputil.h"
#include "mpegvideo.h"
#include "bswap.h"

static VLC svq1_block_type;
static VLC svq1_motion_component;
static VLC svq1_intra_multistage[6];
static VLC svq1_inter_multistage[6];
static VLC svq1_intra_mean;
static VLC svq1_inter_mean;

#define MEDIAN(a,b,c)	(((a < b) != (b >= c)) ? b : (((a < c) != (c > b)) ? c : a))

#define SVQ1_BLOCK_SKIP		0
#define SVQ1_BLOCK_INTER	1
#define SVQ1_BLOCK_INTER_4V	2
#define SVQ1_BLOCK_INTRA	3

/* motion vector (prediction) */
typedef struct svq1_pmv_s {
  int		 x;
  int		 y;
} svq1_pmv_t;

#include "svq1_cb.h"
#include "svq1_vlc.h"

static const uint16_t checksum_table[256] = {
  0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
  0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
  0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
  0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
  0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
  0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
  0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
  0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
  0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
  0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
  0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
  0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
  0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
  0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
  0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
  0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
  0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
  0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
  0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
  0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
  0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
  0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
  0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
  0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
  0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
  0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,
  0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
  0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
  0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
  0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
  0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
  0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
};

static const uint8_t string_table[256] = {
  0x00, 0xD5, 0x7F, 0xAA, 0xFE, 0x2B, 0x81, 0x54,
  0x29, 0xFC, 0x56, 0x83, 0xD7, 0x02, 0xA8, 0x7D,
  0x52, 0x87, 0x2D, 0xF8, 0xAC, 0x79, 0xD3, 0x06,
  0x7B, 0xAE, 0x04, 0xD1, 0x85, 0x50, 0xFA, 0x2F,
  0xA4, 0x71, 0xDB, 0x0E, 0x5A, 0x8F, 0x25, 0xF0,
  0x8D, 0x58, 0xF2, 0x27, 0x73, 0xA6, 0x0C, 0xD9,
  0xF6, 0x23, 0x89, 0x5C, 0x08, 0xDD, 0x77, 0xA2,
  0xDF, 0x0A, 0xA0, 0x75, 0x21, 0xF4, 0x5E, 0x8B,
  0x9D, 0x48, 0xE2, 0x37, 0x63, 0xB6, 0x1C, 0xC9,
  0xB4, 0x61, 0xCB, 0x1E, 0x4A, 0x9F, 0x35, 0xE0,
  0xCF, 0x1A, 0xB0, 0x65, 0x31, 0xE4, 0x4E, 0x9B,
  0xE6, 0x33, 0x99, 0x4C, 0x18, 0xCD, 0x67, 0xB2,
  0x39, 0xEC, 0x46, 0x93, 0xC7, 0x12, 0xB8, 0x6D,
  0x10, 0xC5, 0x6F, 0xBA, 0xEE, 0x3B, 0x91, 0x44,
  0x6B, 0xBE, 0x14, 0xC1, 0x95, 0x40, 0xEA, 0x3F,
  0x42, 0x97, 0x3D, 0xE8, 0xBC, 0x69, 0xC3, 0x16,
  0xEF, 0x3A, 0x90, 0x45, 0x11, 0xC4, 0x6E, 0xBB,
  0xC6, 0x13, 0xB9, 0x6C, 0x38, 0xED, 0x47, 0x92,
  0xBD, 0x68, 0xC2, 0x17, 0x43, 0x96, 0x3C, 0xE9,
  0x94, 0x41, 0xEB, 0x3E, 0x6A, 0xBF, 0x15, 0xC0,
  0x4B, 0x9E, 0x34, 0xE1, 0xB5, 0x60, 0xCA, 0x1F,
  0x62, 0xB7, 0x1D, 0xC8, 0x9C, 0x49, 0xE3, 0x36,
  0x19, 0xCC, 0x66, 0xB3, 0xE7, 0x32, 0x98, 0x4D,
  0x30, 0xE5, 0x4F, 0x9A, 0xCE, 0x1B, 0xB1, 0x64,
  0x72, 0xA7, 0x0D, 0xD8, 0x8C, 0x59, 0xF3, 0x26,
  0x5B, 0x8E, 0x24, 0xF1, 0xA5, 0x70, 0xDA, 0x0F,
  0x20, 0xF5, 0x5F, 0x8A, 0xDE, 0x0B, 0xA1, 0x74,
  0x09, 0xDC, 0x76, 0xA3, 0xF7, 0x22, 0x88, 0x5D,
  0xD6, 0x03, 0xA9, 0x7C, 0x28, 0xFD, 0x57, 0x82,
  0xFF, 0x2A, 0x80, 0x55, 0x01, 0xD4, 0x7E, 0xAB,
  0x84, 0x51, 0xFB, 0x2E, 0x7A, 0xAF, 0x05, 0xD0,
  0xAD, 0x78, 0xD2, 0x07, 0x53, 0x86, 0x2C, 0xF9
};

#define SVQ1_PROCESS_VECTOR()\
    for (; level > 0; i++) {\
      /* process next depth */\
      if (i == m) {\
	m = n;\
	if (--level == 0)\
	  break;\
      }\
      /* divide block if next bit set */\
      if (get_bits (bitbuf, 1) == 0)\
	break;\
      /* add child nodes */\
      list[n++] = list[i];\
      list[n++] = list[i] + (((level & 1) ? pitch : 1) << ((level / 2) + 1));\
    }

#define SVQ1_ADD_CODEBOOK()\
	  /* add codebook entries to vector */\
	  for (j=0; j < stages; j++) {\
	    n3  = codebook[entries[j]] ^ 0x80808080;\
	    n1 += ((n3 & 0xFF00FF00) >> 8);\
	    n2 +=  (n3 & 0x00FF00FF);\
	  }\
\
	  /* clip to [0..255] */\
	  if (n1 & 0xFF00FF00) {\
	    n3  = ((( n1 >> 15) & 0x00010001) | 0x01000100) - 0x00010001;\
	    n1 += 0x7F007F00;\
	    n1 |= (((~n1 >> 15) & 0x00010001) | 0x01000100) - 0x00010001;\
	    n1 &= (n3 & 0x00FF00FF);\
	  }\
\
	  if (n2 & 0xFF00FF00) {\
	    n3  = ((( n2 >> 15) & 0x00010001) | 0x01000100) - 0x00010001;\
	    n2 += 0x7F007F00;\
	    n2 |= (((~n2 >> 15) & 0x00010001) | 0x01000100) - 0x00010001;\
	    n2 &= (n3 & 0x00FF00FF);\
	  }

#define SVQ1_DO_CODEBOOK_INTRA()\
      for (y=0; y < height; y++) {\
	for (x=0; x < (width / 4); x++, codebook++) {\
	n1 = n4;\
	n2 = n4;\
	SVQ1_ADD_CODEBOOK()\
	/* store result */\
	dst[x] = (n1 << 8) | n2;\
	}\
	dst += (pitch / 4);\
      }

#define SVQ1_DO_CODEBOOK_NONINTRA()\
      for (y=0; y < height; y++) {\
	for (x=0; x < (width / 4); x++, codebook++) {\
	n3 = dst[x];\
	/* add mean value to vector */\
	n1 = ((n3 & 0xFF00FF00) >> 8) + n4;\
	n2 =  (n3 & 0x00FF00FF)	  + n4;\
	SVQ1_ADD_CODEBOOK()\
	/* store result */\
	dst[x] = (n1 << 8) | n2;\
	}\
	dst += (pitch / 4);\
      }

#define SVQ1_CALC_CODEBOOK_ENTRIES(cbook)\
      codebook = (const uint32_t *) cbook[level];\
      bit_cache = get_bits (bitbuf, 4*stages);\
      /* calculate codebook entries for this vector */\
      for (j=0; j < stages; j++) {\
	entries[j] = (((bit_cache >> (4*(stages - j - 1))) & 0xF) + 16*j) << (level + 1);\
      }\
      mean -= (stages * 128);\
      n4    = ((mean + (mean >> 31)) << 16) | (mean & 0xFFFF);

static int svq1_decode_block_intra (GetBitContext *bitbuf, uint8_t *pixels, int pitch ) {
  uint32_t    bit_cache;
  uint8_t    *list[63];
  uint32_t   *dst;
  const uint32_t *codebook;
  int	      entries[6];
  int	      i, j, m, n;
  int	      mean, stages;
  unsigned    x, y, width, height, level;
  uint32_t    n1, n2, n3, n4;

  /* initialize list for breadth first processing of vectors */
  list[0] = pixels;

  /* recursively process vector */
  for (i=0, m=1, n=1, level=5; i < n; i++) {
    SVQ1_PROCESS_VECTOR();

    /* destination address and vector size */
    dst = (uint32_t *) list[i];
    width = 1 << ((4 + level) /2);
    height = 1 << ((3 + level) /2);

    /* get number of stages (-1 skips vector, 0 for mean only) */
    stages = get_vlc2(bitbuf, svq1_intra_multistage[level].table, 3, 3) - 1;

    if (stages == -1) {
	for (y=0; y < height; y++) {
	  memset (&dst[y*(pitch / 4)], 0, width);
	}
      continue;		/* skip vector */
    }

    if ((stages > 0) && (level >= 4)) {
#ifdef DEBUG_SVQ1
    printf("Error (svq1_decode_block_intra): invalid vector: stages=%i level=%i\n",stages,level);
#endif
      return -1;	/* invalid vector */
    }

    mean = get_vlc2(bitbuf, svq1_intra_mean.table, 8, 3);

    if (stages == 0) {
      for (y=0; y < height; y++) {
	memset (&dst[y*(pitch / 4)], mean, width);
      }
    } else {
      SVQ1_CALC_CODEBOOK_ENTRIES(svq1_intra_codebooks);
      SVQ1_DO_CODEBOOK_INTRA()
    }
  }

  return 0;
}

static int svq1_decode_block_non_intra (GetBitContext *bitbuf, uint8_t *pixels, int pitch ) {
  uint32_t    bit_cache;
  uint8_t    *list[63];
  uint32_t   *dst;
  const uint32_t *codebook;
  int	      entries[6];
  int	      i, j, m, n;
  int	      mean, stages;
  int	      x, y, width, height, level;
  uint32_t    n1, n2, n3, n4;

  /* initialize list for breadth first processing of vectors */
  list[0] = pixels;

  /* recursively process vector */
  for (i=0, m=1, n=1, level=5; i < n; i++) {
    SVQ1_PROCESS_VECTOR();

    /* destination address and vector size */
    dst = (uint32_t *) list[i];
    width = 1 << ((4 + level) /2);
    height = 1 << ((3 + level) /2);

    /* get number of stages (-1 skips vector, 0 for mean only) */
    stages = get_vlc2(bitbuf, svq1_inter_multistage[level].table, 3, 2) - 1;

    if (stages == -1) continue;	/* skip vector */

    if ((stages > 0) && (level >= 4)) {
#ifdef DEBUG_SVQ1
    printf("Error (svq1_decode_block_non_intra): invalid vector: stages=%i level=%i\n",stages,level);
#endif
      return -1;	/* invalid vector */
    }

    mean = get_vlc2(bitbuf, svq1_inter_mean.table, 9, 3) - 256;

    SVQ1_CALC_CODEBOOK_ENTRIES(svq1_inter_codebooks);
    SVQ1_DO_CODEBOOK_NONINTRA()
  }
  return 0;
}

static int svq1_decode_motion_vector (GetBitContext *bitbuf, svq1_pmv_t *mv, svq1_pmv_t **pmv) {
  int	      diff;
  int	      i;

  for (i=0; i < 2; i++) {

    /* get motion code */
    diff = get_vlc2(bitbuf, svq1_motion_component.table, 7, 2) - 32;

    /* add median of motion vector predictors and clip result */
    if (i == 1)
      mv->y = ((diff + MEDIAN(pmv[0]->y, pmv[1]->y, pmv[2]->y)) << 26) >> 26;
    else
      mv->x = ((diff + MEDIAN(pmv[0]->x, pmv[1]->x, pmv[2]->x)) << 26) >> 26;
  }

  return 0;
}

static void svq1_skip_block (uint8_t *current, uint8_t *previous, int pitch, int x, int y) {
  uint8_t *src;
  uint8_t *dst;
  int	   i;

  src = &previous[x + y*pitch];
  dst = current;

  for (i=0; i < 16; i++) {
    memcpy (dst, src, 16);
    src += pitch;
    dst += pitch;
  }
}

static int svq1_motion_inter_block (MpegEncContext *s, GetBitContext *bitbuf,
			       uint8_t *current, uint8_t *previous, int pitch,
			       svq1_pmv_t *motion, int x, int y) {
  uint8_t    *src;
  uint8_t    *dst;
  svq1_pmv_t  mv;
  svq1_pmv_t *pmv[3];
  int	      result;

  /* predict and decode motion vector */
  pmv[0] = &motion[0];
  if (y == 0) {
    pmv[1] =
    pmv[2] = pmv[0];
  }
  else {
    pmv[1] = &motion[(x / 8) + 2];
    pmv[2] = &motion[(x / 8) + 4];
  }

  result = svq1_decode_motion_vector (bitbuf, &mv, pmv);

  if (result != 0)
    return result;

  motion[0].x		=
  motion[(x / 8) + 2].x	=
  motion[(x / 8) + 3].x	= mv.x;
  motion[0].y		=
  motion[(x / 8) + 2].y	=
  motion[(x / 8) + 3].y	= mv.y;
  
  if(y + (mv.y >> 1)<0)
     mv.y= 0;
  if(x + (mv.x >> 1)<0)
     mv.x= 0;

#if 0
  int w= (s->width+15)&~15;
  int h= (s->height+15)&~15;
  if(x + (mv.x >> 1)<0 || y + (mv.y >> 1)<0 || x + (mv.x >> 1) + 16 > w || y + (mv.y >> 1) + 16> h)
      printf("%d %d %d %d\n", x, y, x + (mv.x >> 1), y + (mv.y >> 1));
#endif
 
  src = &previous[(x + (mv.x >> 1)) + (y + (mv.y >> 1))*pitch];
  dst = current;

  s->dsp.put_pixels_tab[0][((mv.y & 1) << 1) | (mv.x & 1)](dst,src,pitch,16);

  return 0;
}

static int svq1_motion_inter_4v_block (MpegEncContext *s, GetBitContext *bitbuf,
				  uint8_t *current, uint8_t *previous, int pitch,
				  svq1_pmv_t *motion,int x, int y) {
  uint8_t    *src;
  uint8_t    *dst;
  svq1_pmv_t  mv;
  svq1_pmv_t *pmv[4];
  int	      i, result;

  /* predict and decode motion vector (0) */
  pmv[0] = &motion[0];
  if (y == 0) {
    pmv[1] =
    pmv[2] = pmv[0];
  }
  else {
    pmv[1] = &motion[(x / 8) + 2];
    pmv[2] = &motion[(x / 8) + 4];
  }

  result = svq1_decode_motion_vector (bitbuf, &mv, pmv);

  if (result != 0)
    return result;

  /* predict and decode motion vector (1) */
  pmv[0] = &mv;
  if (y == 0) {
    pmv[1] =
    pmv[2] = pmv[0];
  }
  else {
    pmv[1] = &motion[(x / 8) + 3];
  }
  result = svq1_decode_motion_vector (bitbuf, &motion[0], pmv);

  if (result != 0)
    return result;

  /* predict and decode motion vector (2) */
  pmv[1] = &motion[0];
  pmv[2] = &motion[(x / 8) + 1];

  result = svq1_decode_motion_vector (bitbuf, &motion[(x / 8) + 2], pmv);

  if (result != 0)
    return result;

  /* predict and decode motion vector (3) */
  pmv[2] = &motion[(x / 8) + 2];
  pmv[3] = &motion[(x / 8) + 3];

  result = svq1_decode_motion_vector (bitbuf, pmv[3], pmv);

  if (result != 0)
    return result;

  /* form predictions */
  for (i=0; i < 4; i++) {
    int mvx= pmv[i]->x + (i&1)*16;
    int mvy= pmv[i]->y + (i>>1)*16;
  
    ///XXX /FIXME cliping or padding?
    if(y + (mvy >> 1)<0)
       mvy= 0;
    if(x + (mvx >> 1)<0)
       mvx= 0;

#if 0
  int w= (s->width+15)&~15;
  int h= (s->height+15)&~15;
  if(x + (mvx >> 1)<0 || y + (mvy >> 1)<0 || x + (mvx >> 1) + 8 > w || y + (mvy >> 1) + 8> h)
      printf("%d %d %d %d\n", x, y, x + (mvx >> 1), y + (mvy >> 1));
#endif
    src = &previous[(x + (mvx >> 1)) + (y + (mvy >> 1))*pitch];
    dst = current;
    
    s->dsp.put_pixels_tab[1][((mvy & 1) << 1) | (mvx & 1)](dst,src,pitch,8);

    /* select next block */
    if (i & 1) {
      current  += 8*(pitch - 1);
    } else {
      current  += 8;
    }
  }

  return 0;
}

static int svq1_decode_delta_block (MpegEncContext *s, GetBitContext *bitbuf,
			uint8_t *current, uint8_t *previous, int pitch,
			svq1_pmv_t *motion, int x, int y) {
  uint32_t block_type;
  int	   result = 0;

  /* get block type */
  block_type = get_vlc2(bitbuf, svq1_block_type.table, 2, 2);

  /* reset motion vectors */
  if (block_type == SVQ1_BLOCK_SKIP || block_type == SVQ1_BLOCK_INTRA) {
    motion[0].x		  =
    motion[0].y		  =
    motion[(x / 8) + 2].x =
    motion[(x / 8) + 2].y =
    motion[(x / 8) + 3].x =
    motion[(x / 8) + 3].y = 0;
  }

  switch (block_type) {
  case SVQ1_BLOCK_SKIP:
    svq1_skip_block (current, previous, pitch, x, y);
    break;

  case SVQ1_BLOCK_INTER:
    result = svq1_motion_inter_block (s, bitbuf, current, previous, pitch, motion, x, y);

    if (result != 0)
    {
#ifdef DEBUG_SVQ1
    printf("Error in svq1_motion_inter_block %i\n",result);
#endif
      break;
    }
    result = svq1_decode_block_non_intra (bitbuf, current, pitch);
    break;

  case SVQ1_BLOCK_INTER_4V:
    result = svq1_motion_inter_4v_block (s, bitbuf, current, previous, pitch, motion, x, y);

    if (result != 0)
    {
#ifdef DEBUG_SVQ1
    printf("Error in svq1_motion_inter_4v_block %i\n",result);
#endif
      break;
    }
    result = svq1_decode_block_non_intra (bitbuf, current, pitch);
    break;

  case SVQ1_BLOCK_INTRA:
    result = svq1_decode_block_intra (bitbuf, current, pitch);
    break;
  }

  return result;
}

/* standard video sizes */
static struct { int width; int height; } svq1_frame_size_table[8] = {
  { 160, 120 }, { 128,  96 }, { 176, 144 }, { 352, 288 },
  { 704, 576 }, { 240, 180 }, { 320, 240 }, {  -1,  -1 }
};

static uint16_t svq1_packet_checksum (uint8_t *data, int length, int value) {
  int i;

  for (i=0; i < length; i++) {
    value = checksum_table[data[i] ^ (value >> 8)] ^ ((value & 0xFF) << 8);
  }

  return value;
}

static uint16_t svq1_component_checksum (uint16_t *pixels, int pitch,
                                         int width, int height, int value) {
  int x, y;

  for (y=0; y < height; y++) {
    for (x=0; x < width; x++) {
      value = checksum_table[pixels[x] ^ (value >> 8)] ^ ((value & 0xFF) << 8);
    }

    pixels += pitch;
  }

  return value;
}

static void svq1_parse_string (GetBitContext *bitbuf, uint8_t *out) {
  uint8_t seed;
  int     i;

  out[0] = get_bits (bitbuf, 8);

  seed = string_table[out[0]];

  for (i=1; i < out[0]; i++) {
    out[i] = get_bits (bitbuf, 8) ^ seed;
    seed   = string_table[out[i] ^ seed];
  }
}

static int svq1_decode_frame_header (GetBitContext *bitbuf,MpegEncContext *s) {
  int frame_size_code;
  int temporal_reference;

  temporal_reference = get_bits (bitbuf, 8);

  /* frame type */
  s->pict_type= get_bits (bitbuf, 2)+1;
  if(s->pict_type==4) 
      return -1;
      
  if (s->pict_type == I_TYPE) {

    /* unknown fields */
    if (s->f_code == 0x50 || s->f_code == 0x60) {
      int csum = get_bits (bitbuf, 16);

      csum = svq1_packet_checksum ((uint8_t *)bitbuf->buffer, bitbuf->size_in_bits>>3, csum);

//      printf ("%s checksum (%02x) for packet data\n",
//              (csum == 0) ? "correct" : "incorrect", csum);
    }

    if ((s->f_code ^ 0x10) >= 0x50) {
      char msg[256];

      svq1_parse_string (bitbuf, (char *) msg);

      printf ("embedded message: \"%s\"\n", (char *) msg);
    }

    get_bits (bitbuf, 2);
    get_bits (bitbuf, 2);
    get_bits (bitbuf, 1);

    /* load frame size */
    frame_size_code = get_bits (bitbuf, 3);

    if (frame_size_code == 7) {
      /* load width, height (12 bits each) */
      s->width = get_bits (bitbuf, 12);
      s->height = get_bits (bitbuf, 12);

      if (!s->width || !s->height)
        return -1;
    } else {
      /* get width, height from table */
      s->width = svq1_frame_size_table[frame_size_code].width;
      s->height = svq1_frame_size_table[frame_size_code].height;
    }
  }

  /* unknown fields */
  if (get_bits (bitbuf, 1) == 1) {
    get_bits (bitbuf, 1);       /* use packet checksum if (1) */
    get_bits (bitbuf, 1);       /* component checksums after image data if (1) */

    if (get_bits (bitbuf, 2) != 0)
      return -1;
  }

  if (get_bits (bitbuf, 1) == 1) {
    get_bits (bitbuf, 1);
    get_bits (bitbuf, 4);
    get_bits (bitbuf, 1);
    get_bits (bitbuf, 2);

    while (get_bits (bitbuf, 1) == 1) {
      get_bits (bitbuf, 8);
    }
  }
  
  return 0;
}

static int svq1_decode_frame(AVCodecContext *avctx, 
                             void *data, int *data_size,
                             uint8_t *buf, int buf_size)
{
  MpegEncContext *s=avctx->priv_data;
  uint8_t      *current, *previous;
  int		result, i, x, y, width, height;
  AVFrame *pict = data; 

  /* initialize bit buffer */
  init_get_bits(&s->gb,buf,buf_size*8);

  /* decode frame header */
  s->f_code = get_bits (&s->gb, 22);

  if ((s->f_code & ~0x70) || !(s->f_code & 0x60))
    return -1;

  /* swap some header bytes (why?) */
  if (s->f_code != 0x20) {
    uint32_t *src = (uint32_t *) (buf + 4);

    for (i=0; i < 4; i++) {
      src[i] = ((src[i] << 16) | (src[i] >> 16)) ^ src[7 - i];
    }
  }

  result = svq1_decode_frame_header (&s->gb, s);

  if (result != 0)
  {
#ifdef DEBUG_SVQ1
    printf("Error in svq1_decode_frame_header %i\n",result);
#endif
    return result;
  }
  
  //FIXME this avoids some confusion for "B frames" without 2 references
  //this should be removed after libavcodec can handle more flaxible picture types & ordering
  if(s->pict_type==B_TYPE && s->last_picture_ptr==NULL) return buf_size;
  
  if(avctx->hurry_up && s->pict_type==B_TYPE) return buf_size;

  if(MPV_frame_start(s, avctx) < 0)
      return -1;

  /* decode y, u and v components */
  for (i=0; i < 3; i++) {
    int linesize;
    if (i == 0) {
      width  = (s->width+15)&~15;
      height = (s->height+15)&~15;
      linesize= s->linesize;
    } else {
      if(s->flags&CODEC_FLAG_GRAY) break;
      width  = (s->width/4+15)&~15;
      height = (s->height/4+15)&~15;
      linesize= s->uvlinesize;
    }

    current  = s->current_picture.data[i];

    if(s->pict_type==B_TYPE){
        previous = s->next_picture.data[i];
    }else{
        previous = s->last_picture.data[i];
    }

    if (s->pict_type == I_TYPE) {
      /* keyframe */
      for (y=0; y < height; y+=16) {
	for (x=0; x < width; x+=16) {
	  result = svq1_decode_block_intra (&s->gb, &current[x], linesize);
	  if (result != 0)
	  {
#ifdef DEBUG_SVQ1
	    printf("Error in svq1_decode_block %i (keyframe)\n",result);
#endif
	    return result;
	  }
	}
	current += 16*linesize;
      }
    } else {
      svq1_pmv_t pmv[width/8+3];
      /* delta frame */
      memset (pmv, 0, ((width / 8) + 3) * sizeof(svq1_pmv_t));

      for (y=0; y < height; y+=16) {
	for (x=0; x < width; x+=16) {
	  result = svq1_decode_delta_block (s, &s->gb, &current[x], previous,
					    linesize, pmv, x, y);
	  if (result != 0)
	  {
#ifdef DEBUG_SVQ1
    printf("Error in svq1_decode_delta_block %i\n",result);
#endif
	    return result;
	  }
	}

	pmv[0].x =
	pmv[0].y = 0;

	current += 16*linesize;
      }
    }
  }
  
  *pict = *(AVFrame*)&s->current_picture;


  MPV_frame_end(s);
  
  *data_size=sizeof(AVFrame);
  return buf_size;
}

static int svq1_decode_init(AVCodecContext *avctx)
{
    MpegEncContext *s = avctx->priv_data;
    int i;

    s->avctx = avctx;
    s->width = (avctx->width+3)&~3;
    s->height = (avctx->height+3)&~3;
    s->codec_id= avctx->codec->id;
    avctx->pix_fmt = PIX_FMT_YUV410P;
    avctx->has_b_frames= 1; // not true, but DP frames and these behave like unidirectional b frames
    s->flags= avctx->flags;
    if (MPV_common_init(s) < 0) return -1;

    init_vlc(&svq1_block_type, 2, 4,
        &svq1_block_type_vlc[0][1], 2, 1,
        &svq1_block_type_vlc[0][0], 2, 1);

    init_vlc(&svq1_motion_component, 7, 65,
        &svq1_motion_component_vlc[0][1], 4, 2,
        &svq1_motion_component_vlc[0][0], 4, 2);

    for (i = 0; i < 6; i++) {
        init_vlc(&svq1_intra_multistage[i], 3, 8,
            &svq1_intra_multistage_vlc[i][0][1], 2, 1,
            &svq1_intra_multistage_vlc[i][0][0], 2, 1);
        init_vlc(&svq1_inter_multistage[i], 3, 8,
            &svq1_inter_multistage_vlc[i][0][1], 2, 1,
            &svq1_inter_multistage_vlc[i][0][0], 2, 1);
    }

    init_vlc(&svq1_intra_mean, 8, 256,
        &svq1_intra_mean_vlc[0][1], 4, 2,
        &svq1_intra_mean_vlc[0][0], 4, 2);

    init_vlc(&svq1_inter_mean, 9, 512,
        &svq1_inter_mean_vlc[0][1], 4, 2,
        &svq1_inter_mean_vlc[0][0], 4, 2);

    return 0;
}

static int svq1_decode_end(AVCodecContext *avctx)
{
    MpegEncContext *s = avctx->priv_data;

    MPV_common_end(s);
    return 0;
}

AVCodec svq1_decoder = {
    "svq1",
    CODEC_TYPE_VIDEO,
    CODEC_ID_SVQ1,
    sizeof(MpegEncContext),
    svq1_decode_init,
    NULL,
    svq1_decode_end,
    svq1_decode_frame,
    CODEC_CAP_DR1,
};