/*
  * H261 decoder
  * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
  * Copyright (c) 2004 Maarten Daniels
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg 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 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg 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 FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**

  * @file

  * H.261 decoder.
  */
 

 #include "libavutil/avassert.h"

 #include "avcodec.h"

 #include "mpeg_er.h"

 #include "mpegutils.h"

 #include "mpegvideo.h"

 #include "h263.h"

 #include "h261.h"

 #include "internal.h"

 
 #define H261_MBA_VLC_BITS 9
 #define H261_MTYPE_VLC_BITS 6
 #define H261_MV_VLC_BITS 7
 #define H261_CBP_VLC_BITS 9
 #define TCOEFF_VLC_BITS 9
 #define MBA_STUFFING 33
 #define MBA_STARTCODE 34
 
 static VLC h261_mba_vlc;
 static VLC h261_mtype_vlc;
 static VLC h261_mv_vlc;
 static VLC h261_cbp_vlc;
 

 static av_cold void h261_decode_init_vlc(H261Context *h)
 {

     static int done = 0;
 

     if (!done) {

         done = 1;

         INIT_VLC_STATIC(&h261_mba_vlc, H261_MBA_VLC_BITS, 35,

                         ff_h261_mba_bits, 1, 1,
                         ff_h261_mba_code, 1, 1, 662);

         INIT_VLC_STATIC(&h261_mtype_vlc, H261_MTYPE_VLC_BITS, 10,

                         ff_h261_mtype_bits, 1, 1,
                         ff_h261_mtype_code, 1, 1, 80);

         INIT_VLC_STATIC(&h261_mv_vlc, H261_MV_VLC_BITS, 17,

                         &ff_h261_mv_tab[0][1], 2, 1,
                         &ff_h261_mv_tab[0][0], 2, 1, 144);

         INIT_VLC_STATIC(&h261_cbp_vlc, H261_CBP_VLC_BITS, 63,

                         &ff_h261_cbp_tab[0][1], 2, 1,
                         &ff_h261_cbp_tab[0][0], 2, 1, 512);

         INIT_VLC_RL(ff_h261_rl_tcoeff, 552);

     }
 }
 

 static av_cold int h261_decode_init(AVCodecContext *avctx)
 {
     H261Context *h          = avctx->priv_data;
     MpegEncContext *const s = &h->s;

 
     // set defaults

     ff_mpv_decode_defaults(s);

     ff_mpv_decode_init(s, avctx);
 

     s->out_format  = FMT_H261;
     s->low_delay   = 1;
     avctx->pix_fmt = AV_PIX_FMT_YUV420P;

     ff_h261_common_init();

     h261_decode_init_vlc(h);
 
     h->gob_start_code_skipped = 0;
 
     return 0;
 }
 
 /**

  * Decode the group of blocks header or slice header.

  * @return <0 if an error occurred

  */

 static int h261_decode_gob_header(H261Context *h)
 {

     unsigned int val;

     MpegEncContext *const s = &h->s;

     if (!h->gob_start_code_skipped) {

         /* Check for GOB Start Code */
         val = show_bits(&s->gb, 15);

         if (val)

             return -1;
 
         /* We have a GBSC */
         skip_bits(&s->gb, 16);
     }
 
     h->gob_start_code_skipped = 0;
 
     h->gob_number = get_bits(&s->gb, 4); /* GN */

     s->qscale     = get_bits(&s->gb, 5); /* GQUANT */

 
     /* Check if gob_number is valid */

     if (s->mb_height == 18) { // CIF
         if ((h->gob_number <= 0) || (h->gob_number > 12))

             return -1;

     } else { // QCIF
         if ((h->gob_number != 1) && (h->gob_number != 3) &&
             (h->gob_number != 5))

             return -1;
     }
 
     /* GEI */

     if (skip_1stop_8data_bits(&s->gb) < 0)
         return AVERROR_INVALIDDATA;

     if (s->qscale == 0) {

         av_log(s->avctx, AV_LOG_ERROR, "qscale has forbidden 0 value\n");

         if (s->avctx->err_recognition & (AV_EF_BITSTREAM | AV_EF_COMPLIANT))

             return -1;
     }

     /* For the first transmitted macroblock in a GOB, MBA is the absolute
      * address. For subsequent macroblocks, MBA is the difference between
      * the absolute addresses of the macroblock and the last transmitted
      * macroblock. */

     h->current_mba = 0;

     h->mba_diff    = 0;

 
     return 0;
 }
 
 /**

  * Decode the group of blocks / video packet header.

  * @return <0 if no resync found
  */

 static int h261_resync(H261Context *h)

 {
     MpegEncContext *const s = &h->s;

     int left, ret;
 

     if (h->gob_start_code_skipped) {
         ret = h261_decode_gob_header(h);
         if (ret >= 0)

             return 0;

     } else {
         if (show_bits(&s->gb, 15) == 0) {
             ret = h261_decode_gob_header(h);
             if (ret >= 0)

                 return 0;
         }

         // OK, it is not where it is supposed to be ...
         s->gb = s->last_resync_gb;

         align_get_bits(&s->gb);

         left = get_bits_left(&s->gb);

         for (; left > 15 + 1 + 4 + 5; left -= 8) {
             if (show_bits(&s->gb, 15) == 0) {
                 GetBitContext bak = s->gb;

                 ret = h261_decode_gob_header(h);
                 if (ret >= 0)

                     return 0;
 

                 s->gb = bak;

             }
             skip_bits(&s->gb, 8);
         }
     }
 
     return -1;
 }
 
 /**

  * Decode skipped macroblocks.

  * @return 0
  */

 static int h261_decode_mb_skipped(H261Context *h, int mba1, int mba2)

 {

     MpegEncContext *const s = &h->s;

     int i;
 
     s->mb_intra = 0;
 

     for (i = mba1; i < mba2; i++) {

         int j, xy;
 

         s->mb_x = ((h->gob_number - 1) % 2) * 11 + i % 11;
         s->mb_y = ((h->gob_number - 1) / 2) * 3 + i / 11;
         xy      = s->mb_x + s->mb_y * s->mb_stride;

         ff_init_block_index(s);
         ff_update_block_index(s);
 

         for (j = 0; j < 6; j++)

             s->block_last_index[j] = -1;
 

         s->mv_dir                      = MV_DIR_FORWARD;
         s->mv_type                     = MV_TYPE_16X16;

         s->current_picture.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;

         s->mv[0][0][0]                 = 0;
         s->mv[0][0][1]                 = 0;
         s->mb_skipped                  = 1;
         h->mtype                      &= ~MB_TYPE_H261_FIL;

         if (s->current_picture.motion_val[0]) {
             int b_stride = 2*s->mb_width + 1;
             int b_xy     = 2 * s->mb_x + (2 * s->mb_y) * b_stride;
             s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
             s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
         }
 

         ff_mpv_decode_mb(s, s->block);

     }
 
     return 0;
 }
 

 static const int mvmap[17] = {
     0, -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, -16
 };
 

 static int decode_mv_component(GetBitContext *gb, int v)
 {

     int mv_diff = get_vlc2(gb, h261_mv_vlc.table, H261_MV_VLC_BITS, 2);
 
     /* check if mv_diff is valid */

     if (mv_diff < 0)

         return v;
 
     mv_diff = mvmap[mv_diff];
 

     if (mv_diff && !get_bits1(gb))
         mv_diff = -mv_diff;

 
     v += mv_diff;

     if (v <= -16)
         v += 32;
     else if (v >= 16)
         v -= 32;

 
     return v;
 }
 

 /**
  * Decode a macroblock.
  * @return <0 if an error occurred
  */
 static int h261_decode_block(H261Context *h, int16_t *block, int n, int coded)
 {
     MpegEncContext *const s = &h->s;

     int level, i, j, run;

     RLTable *rl = &ff_h261_rl_tcoeff;

     const uint8_t *scan_table;
 
     /* For the variable length encoding there are two code tables, one being
      * used for the first transmitted LEVEL in INTER, INTER + MC and
      * INTER + MC + FIL blocks, the second for all other LEVELs except the
      * first one in INTRA blocks which is fixed length coded with 8 bits.
      * NOTE: The two code tables only differ in one VLC so we handle that
      * manually. */
     scan_table = s->intra_scantable.permutated;
     if (s->mb_intra) {
         /* DC coef */
         level = get_bits(&s->gb, 8);
         // 0 (00000000b) and -128 (10000000b) are FORBIDDEN
         if ((level & 0x7F) == 0) {
             av_log(s->avctx, AV_LOG_ERROR, "illegal dc %d at %d %d\n",
                    level, s->mb_x, s->mb_y);
             return -1;
         }
         /* The code 1000 0000 is not used, the reconstruction level of 1024
          * being coded as 1111 1111. */
         if (level == 255)
             level = 128;
         block[0] = level;
         i        = 1;
     } else if (coded) {
         // Run  Level   Code
         // EOB          Not possible for first level when cbp is available (that's why the table is different)
         // 0    1       1s
         // *    *       0*
         int check = show_bits(&s->gb, 2);
         i = 0;
         if (check & 0x2) {
             skip_bits(&s->gb, 2);
             block[0] = (check & 0x1) ? -1 : 1;
             i        = 1;
         }
     } else {
         i = 0;
     }
     if (!coded) {
         s->block_last_index[n] = i - 1;
         return 0;
     }

     {
     OPEN_READER(re, &s->gb);

     i--; // offset by -1 to allow direct indexing of scan_table

     for (;;) {

         UPDATE_CACHE(re, &s->gb);
         GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TCOEFF_VLC_BITS, 2, 0);
         if (run == 66) {

             if (level) {
                 CLOSE_READER(re, &s->gb);
                 av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n",
                        s->mb_x, s->mb_y);
                 return -1;
             }

             /* escape */
             /* The remaining combinations of (run, level) are encoded with a
              * 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits
              * level. */

             run   = SHOW_UBITS(re, &s->gb, 6) + 1;

             SKIP_CACHE(re, &s->gb, 6);
             level = SHOW_SBITS(re, &s->gb, 8);
             SKIP_COUNTER(re, &s->gb, 6 + 8);
         } else if (level == 0) {

             break;
         } else {

             if (SHOW_UBITS(re, &s->gb, 1))

                 level = -level;

             SKIP_COUNTER(re, &s->gb, 1);

         }
         i += run;

         if (i >= 64) {

             CLOSE_READER(re, &s->gb);

             av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n",
                    s->mb_x, s->mb_y);
             return -1;
         }

         j        = scan_table[i];

         block[j] = level;
     }

     CLOSE_READER(re, &s->gb);
     }

     s->block_last_index[n] = i;

     return 0;
 }
 

 static int h261_decode_mb(H261Context *h)
 {
     MpegEncContext *const s = &h->s;

     int i, cbp, xy;

 
     cbp = 63;
     // Read mba

     do {
         h->mba_diff = get_vlc2(&s->gb, h261_mba_vlc.table,
                                H261_MBA_VLC_BITS, 2);

 
         /* Check for slice end */
         /* NOTE: GOB can be empty (no MB data) or exist only of MBA_stuffing */

         if (h->mba_diff == MBA_STARTCODE) { // start code

             h->gob_start_code_skipped = 1;
             return SLICE_END;
         }

     } while (h->mba_diff == MBA_STUFFING); // stuffing

     if (h->mba_diff < 0) {

         if (get_bits_left(&s->gb) <= 7)

             return SLICE_END;
 
         av_log(s->avctx, AV_LOG_ERROR, "illegal mba at %d %d\n", s->mb_x, s->mb_y);
         return SLICE_ERROR;
     }
 

     h->mba_diff    += 1;

     h->current_mba += h->mba_diff;
 

     if (h->current_mba > MBA_STUFFING)

         return SLICE_ERROR;
 

     s->mb_x = ((h->gob_number - 1) % 2) * 11 + ((h->current_mba - 1) % 11);
     s->mb_y = ((h->gob_number - 1) / 2) * 3 + ((h->current_mba - 1) / 11);
     xy      = s->mb_x + s->mb_y * s->mb_stride;

     ff_init_block_index(s);
     ff_update_block_index(s);
 
     // Read mtype
     h->mtype = get_vlc2(&s->gb, h261_mtype_vlc.table, H261_MTYPE_VLC_BITS, 2);

     if (h->mtype < 0) {

         av_log(s->avctx, AV_LOG_ERROR, "Invalid mtype index %d\n",
                h->mtype);

         return SLICE_ERROR;
     }

     av_assert0(h->mtype < FF_ARRAY_ELEMS(ff_h261_mtype_map));

     h->mtype = ff_h261_mtype_map[h->mtype];

 
     // Read mquant

     if (IS_QUANT(h->mtype))

         ff_set_qscale(s, get_bits(&s->gb, 5));
 
     s->mb_intra = IS_INTRA4x4(h->mtype);
 
     // Read mv

     if (IS_16X16(h->mtype)) {
         /* Motion vector data is included for all MC macroblocks. MVD is
          * obtained from the macroblock vector by subtracting the vector
          * of the preceding macroblock. For this calculation the vector
          * of the preceding macroblock is regarded as zero in the
          * following three situations:
          * 1) evaluating MVD for macroblocks 1, 12 and 23;
          * 2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
          * 3) MTYPE of the previous macroblock was not MC. */
         if ((h->current_mba ==  1) || (h->current_mba == 12) ||
             (h->current_mba == 23) || (h->mba_diff != 1)) {

             h->current_mv_x = 0;
             h->current_mv_y = 0;
         }
 

         h->current_mv_x = decode_mv_component(&s->gb, h->current_mv_x);
         h->current_mv_y = decode_mv_component(&s->gb, h->current_mv_y);
     } else {

         h->current_mv_x = 0;
         h->current_mv_y = 0;
     }
 
     // Read cbp

     if (HAS_CBP(h->mtype))

         cbp = get_vlc2(&s->gb, h261_cbp_vlc.table, H261_CBP_VLC_BITS, 2) + 1;
 

     if (s->mb_intra) {

         s->current_picture.mb_type[xy] = MB_TYPE_INTRA;

         goto intra;
     }
 
     //set motion vectors

     s->mv_dir                      = MV_DIR_FORWARD;
     s->mv_type                     = MV_TYPE_16X16;

     s->current_picture.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;

     s->mv[0][0][0]                 = h->current_mv_x * 2; // gets divided by 2 in motion compensation
     s->mv[0][0][1]                 = h->current_mv_y * 2;

     if (s->current_picture.motion_val[0]) {

         int b_stride = 2*s->mb_width + 1;
         int b_xy     = 2 * s->mb_x + (2 * s->mb_y) * b_stride;

         s->current_picture.motion_val[0][b_xy][0] = s->mv[0][0][0];
         s->current_picture.motion_val[0][b_xy][1] = s->mv[0][0][1];
     }
 

 intra:
     /* decode each block */

     if (s->mb_intra || HAS_CBP(h->mtype)) {

         s->bdsp.clear_blocks(s->block[0]);

         for (i = 0; i < 6; i++) {

             if (h261_decode_block(h, s->block[i], i, cbp & 32) < 0)

                 return SLICE_ERROR;

             cbp += cbp;

         }

     } else {

         for (i = 0; i < 6; i++)

             s->block_last_index[i] = -1;

     }
 

     ff_mpv_decode_mb(s, s->block);

 
     return SLICE_OK;
 }
 
 /**

  * Decode the H.261 picture header.

  * @return <0 if no startcode found
  */

 static int h261_decode_picture_header(H261Context *h)
 {
     MpegEncContext *const s = &h->s;

     int format, i;

     uint32_t startcode = 0;

     for (i = get_bits_left(&s->gb); i > 24; i -= 1) {

         startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;
 

         if (startcode == 0x10)

             break;
     }
 

     if (startcode != 0x10) {

         av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
         return -1;
     }
 
     /* temporal reference */

     i = get_bits(&s->gb, 5); /* picture timestamp */
     if (i < (s->picture_number & 31))

         i += 32;

     s->picture_number = (s->picture_number & ~31) + i;

     s->avctx->framerate = (AVRational) { 30000, 1001 };

 
     /* PTYPE starts here */
     skip_bits1(&s->gb); /* split screen off */
     skip_bits1(&s->gb); /* camera  off */
     skip_bits1(&s->gb); /* freeze picture release off */
 
     format = get_bits1(&s->gb);
 

     // only 2 formats possible
     if (format == 0) { // QCIF
         s->width     = 176;
         s->height    = 144;
         s->mb_width  = 11;

         s->mb_height = 9;

     } else { // CIF
         s->width     = 352;
         s->height    = 288;
         s->mb_width  = 22;

         s->mb_height = 18;
     }
 
     s->mb_num = s->mb_width * s->mb_height;
 
     skip_bits1(&s->gb); /* still image mode off */
     skip_bits1(&s->gb); /* Reserved */
 
     /* PEI */

     if (skip_1stop_8data_bits(&s->gb) < 0)
         return AVERROR_INVALIDDATA;

     /* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first
      * frame, the codec crashes if it does not contain all I-blocks
      * (e.g. when a packet is lost). */

     s->pict_type = AV_PICTURE_TYPE_P;

 
     h->gob_number = 0;
     return 0;
 }
 

 static int h261_decode_gob(H261Context *h)
 {
     MpegEncContext *const s = &h->s;

 
     ff_set_qscale(s, s->qscale);
 
     /* decode mb's */

     while (h->current_mba <= MBA_STUFFING) {

         int ret;
         /* DCT & quantize */

         ret = h261_decode_mb(h);
         if (ret < 0) {
             if (ret == SLICE_END) {

                 h261_decode_mb_skipped(h, h->current_mba, 33);
                 return 0;
             }

             av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n",
                    s->mb_x + s->mb_y * s->mb_stride);

             return -1;
         }
 

         h261_decode_mb_skipped(h,
                                h->current_mba - h->mba_diff,
                                h->current_mba - 1);

     }
 
     return -1;
 }
 
 /**
  * returns the number of bytes consumed for building the current frame
  */

 static int get_consumed_bytes(MpegEncContext *s, int buf_size)
 {
     int pos = get_bits_count(&s->gb) >> 3;
     if (pos == 0)
         pos = 1;      // avoid infinite loops (i doubt that is needed but ...)
     if (pos + 10 > buf_size)
         pos = buf_size;               // oops ;)

 
     return pos;
 }
 

 static int h261_decode_frame(AVCodecContext *avctx, void *data,
                              int *got_frame, AVPacket *avpkt)

 {

     const uint8_t *buf = avpkt->data;

     int buf_size       = avpkt->size;
     H261Context *h     = avctx->priv_data;
     MpegEncContext *s  = &h->s;

     int ret;
     AVFrame *pict = data;
 

     ff_dlog(avctx, "*****frame %d size=%d\n", avctx->frame_number, buf_size);
     ff_dlog(avctx, "bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);

     h->gob_start_code_skipped = 0;

 
 retry:

     init_get_bits(&s->gb, buf, buf_size * 8);

     if (!s->context_initialized)

         // we need the IDCT permutaton for reading a custom matrix

         ff_mpv_idct_init(s);

 
     ret = h261_decode_picture_header(h);
 
     /* skip if the header was thrashed */

     if (ret < 0) {

         av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
         return -1;
     }
 

     if (s->width != avctx->coded_width || s->height != avctx->coded_height) {
         ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat
         s->parse_context.buffer = 0;

         ff_mpv_common_end(s);

         s->parse_context = pc;

     }

     if (!s->context_initialized) {

         if ((ret = ff_mpv_common_init(s)) < 0)

             return ret;
 

         ret = ff_set_dimensions(avctx, s->width, s->height);
         if (ret < 0)
             return ret;

 
         goto retry;
     }
 

     // for skipping the frame

     s->current_picture.f->pict_type = s->pict_type;
     s->current_picture.f->key_frame = s->pict_type == AV_PICTURE_TYPE_I;

     if ((avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B) ||
         (avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type != AV_PICTURE_TYPE_I) ||
          avctx->skip_frame >= AVDISCARD_ALL)

         return get_consumed_bytes(s, buf_size);
 

     if (ff_mpv_frame_start(s, avctx) < 0)

         return -1;
 

     ff_mpeg_er_frame_start(s);

 
     /* decode each macroblock */

     s->mb_x = 0;
     s->mb_y = 0;

     while (h->gob_number < (s->mb_height == 18 ? 12 : 5)) {

         if (h261_resync(h) < 0)

             break;
         h261_decode_gob(h);
     }

     ff_mpv_frame_end(s);

     av_assert0(s->current_picture.f->pict_type == s->current_picture_ptr->f->pict_type);
     av_assert0(s->current_picture.f->pict_type == s->pict_type);

     if ((ret = av_frame_ref(pict, s->current_picture_ptr->f)) < 0)

         return ret;

     ff_print_debug_info(s, s->current_picture_ptr, pict);

     *got_frame = 1;

 
     return get_consumed_bytes(s, buf_size);
 }
 

 static av_cold int h261_decode_end(AVCodecContext *avctx)

 {

     H261Context *h    = avctx->priv_data;

     MpegEncContext *s = &h->s;
 

     ff_mpv_common_end(s);

     return 0;
 }
 

 AVCodec ff_h261_decoder = {

     .name           = "h261",

     .long_name      = NULL_IF_CONFIG_SMALL("H.261"),

     .type           = AVMEDIA_TYPE_VIDEO,

     .id             = AV_CODEC_ID_H261,

     .priv_data_size = sizeof(H261Context),
     .init           = h261_decode_init,
     .close          = h261_decode_end,
     .decode         = h261_decode_frame,
     .capabilities   = CODEC_CAP_DR1,

     .max_lowres     = 3,

 };