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/*

 * Discworld II BMV video decoder

 * Copyright (c) 2011 Konstantin Shishkov

 *

 * 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

 */

#include "libavutil/avassert.h"

#include "libavutil/common.h"

#include "avcodec.h"

#include "bytestream.h"

#include "internal.h"

enum BMVFlags{

    BMV_NOP = 0,

    BMV_END,

    BMV_DELTA,

    BMV_INTRA,

    BMV_SCROLL  = 0x04,

    BMV_PALETTE = 0x08,

    BMV_COMMAND = 0x10,

    BMV_AUDIO   = 0x20,

    BMV_EXT     = 0x40,

    BMV_PRINT   = 0x80

};

#define SCREEN_WIDE 640

#define SCREEN_HIGH 429

typedef struct BMVDecContext {

    AVCodecContext *avctx;

    uint8_t *frame, frame_base[SCREEN_WIDE * (SCREEN_HIGH + 1)];

    uint32_t pal[256];

    const uint8_t *stream;

} BMVDecContext;

#define NEXT_BYTE(v) (v) = forward ? (v) + 1 : (v) - 1;

static int decode_bmv_frame(const uint8_t *source, int src_len, uint8_t *frame, int frame_off)

{

    unsigned val, saved_val = 0;

    int tmplen = src_len;

    const uint8_t *src, *source_end = source + src_len;

    uint8_t *frame_end = frame + SCREEN_WIDE * SCREEN_HIGH;

    uint8_t *dst, *dst_end;

    int len, mask;

    int forward = (frame_off <= -SCREEN_WIDE) || (frame_off >= 0);

    int read_two_nibbles, flag;

    int advance_mode;

    int mode = 0;

    int i;

    if (src_len <= 0)

        return AVERROR_INVALIDDATA;

    if (forward) {

        src = source;

        dst = frame;

        dst_end = frame_end;

    } else {

        src = source + src_len - 1;

        dst = frame_end - 1;

        dst_end = frame - 1;

    }

    for (;;) {

        int shift = 0;

        flag = 0;

        /* The mode/len decoding is a bit strange:

         * values are coded as variable-length codes with nibble units,

         * code end is signalled by two top bits in the nibble being nonzero.

         * And since data is bytepacked and we read two nibbles at a time,

         * we may get a nibble belonging to the next code.

         * Hence this convoluted loop.

         */

        if (!mode || (tmplen == 4)) {

            if (src < source || src >= source_end)

                return AVERROR_INVALIDDATA;

            val = *src;

            read_two_nibbles = 1;

        } else {

            val = saved_val;

            read_two_nibbles = 0;

        }

        if (!(val & 0xC)) {

            for (;;) {

                if(shift>22)

                    return -1;

                if (!read_two_nibbles) {

                    if (src < source || src >= source_end)

                        return AVERROR_INVALIDDATA;

                    shift += 2;

                    val |= *src << shift;

                    if (*src & 0xC)

                        break;

                }

                // two upper bits of the nibble is zero,

                // so shift top nibble value down into their place

                read_two_nibbles = 0;

                shift += 2;

                mask = (1 << shift) - 1;

                val = ((val >> 2) & ~mask) | (val & mask);

                NEXT_BYTE(src);

                if ((val & (0xC << shift))) {

                    flag = 1;

                    break;

                }

            }

        } else if (mode) {

            flag = tmplen != 4;

        }

        if (flag) {

            tmplen = 4;

        } else {

            saved_val = val >> (4 + shift);

            tmplen = 0;

            val &= (1 << (shift + 4)) - 1;

            NEXT_BYTE(src);

        }

        advance_mode = val & 1;

        len = (val >> 1) - 1;

        av_assert0(len>0);

        mode += 1 + advance_mode;

        if (mode >= 4)

            mode -= 3;

        if (len <= 0 || FFABS(dst_end - dst) < len)

            return AVERROR_INVALIDDATA;

        switch (mode) {

        case 1:

            if (forward) {

                if (dst - frame + SCREEN_WIDE < frame_off ||

                        dst - frame + SCREEN_WIDE + frame_off < 0 ||

                        frame_end - dst < frame_off + len ||

                        frame_end - dst < len)

                    return AVERROR_INVALIDDATA;

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

                    dst[i] = dst[frame_off + i];

                dst += len;

            } else {

                dst -= len;

                if (dst - frame + SCREEN_WIDE < frame_off ||

                        dst - frame + SCREEN_WIDE + frame_off < 0 ||

                        frame_end - dst < frame_off + len ||

                        frame_end - dst < len)

                    return AVERROR_INVALIDDATA;

                for (i = len - 1; i >= 0; i--)

                    dst[i] = dst[frame_off + i];

            }

            break;

        case 2:

            if (forward) {

                if (source + src_len - src < len)

                    return AVERROR_INVALIDDATA;

                memcpy(dst, src, len);

                dst += len;

                src += len;

            } else {

                if (src - source < len)

                    return AVERROR_INVALIDDATA;

                dst -= len;

                src -= len;

                memcpy(dst, src, len);

            }

            break;

        case 3:

            val = forward ? dst[-1] : dst[1];

            if (forward) {

                memset(dst, val, len);

                dst += len;

            } else {

                dst -= len;

                memset(dst, val, len);

            }

            break;

        }

        if (dst == dst_end)

            return 0;

    }

    return 0;

}

static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,

                        AVPacket *pkt)

{

    BMVDecContext * const c = avctx->priv_data;

    AVFrame *frame = data;

    int type, scr_off;

    int i, ret;

    uint8_t *srcptr, *outptr;

    c->stream = pkt->data;

    type = bytestream_get_byte(&c->stream);

    if (type & BMV_AUDIO) {

        int blobs = bytestream_get_byte(&c->stream);

        if (pkt->size < blobs * 65 + 2) {

            av_log(avctx, AV_LOG_ERROR, "Audio data doesn't fit in frame\n");

            return AVERROR_INVALIDDATA;

        }

        c->stream += blobs * 65;

    }

    if (type & BMV_COMMAND) {

        int command_size = (type & BMV_PRINT) ? 8 : 10;

        if (c->stream - pkt->data + command_size > pkt->size) {

            av_log(avctx, AV_LOG_ERROR, "Command data doesn't fit in frame\n");

            return AVERROR_INVALIDDATA;

        }

        c->stream += command_size;

    }

    if (type & BMV_PALETTE) {

        if (c->stream - pkt->data > pkt->size - 768) {

            av_log(avctx, AV_LOG_ERROR, "Palette data doesn't fit in frame\n");

            return AVERROR_INVALIDDATA;

        }

        for (i = 0; i < 256; i++)

            c->pal[i] = 0xFFU << 24 | bytestream_get_be24(&c->stream);

    }

    if (type & BMV_SCROLL) {

        if (c->stream - pkt->data > pkt->size - 2) {

            av_log(avctx, AV_LOG_ERROR, "Screen offset data doesn't fit in frame\n");

            return AVERROR_INVALIDDATA;

        }

        scr_off = (int16_t)bytestream_get_le16(&c->stream);

    } else if ((type & BMV_INTRA) == BMV_INTRA) {

        scr_off = -640;

    } else {

        scr_off = 0;

    }

    if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)

        return ret;

    if (decode_bmv_frame(c->stream, pkt->size - (c->stream - pkt->data), c->frame, scr_off)) {

        av_log(avctx, AV_LOG_ERROR, "Error decoding frame data\n");

        return AVERROR_INVALIDDATA;

    }

    memcpy(frame->data[1], c->pal, AVPALETTE_SIZE);

    frame->palette_has_changed = type & BMV_PALETTE;

    outptr = frame->data[0];

    srcptr = c->frame;

    for (i = 0; i < avctx->height; i++) {

        memcpy(outptr, srcptr, avctx->width);

        srcptr += avctx->width;

        outptr += frame->linesize[0];

    }

    *got_frame = 1;

    /* always report that the buffer was completely consumed */

    return pkt->size;

}

static av_cold int decode_init(AVCodecContext *avctx)

{

    BMVDecContext * const c = avctx->priv_data;

    c->avctx = avctx;

    avctx->pix_fmt = AV_PIX_FMT_PAL8;

    if (avctx->width != SCREEN_WIDE || avctx->height != SCREEN_HIGH) {

        av_log(avctx, AV_LOG_ERROR, "Invalid dimension %dx%d\n", avctx->width, avctx->height);

        return AVERROR_INVALIDDATA;

    }

    c->frame = c->frame_base + 640;

    return 0;

}

AVCodec ff_bmv_video_decoder = {

    .name           = "bmv_video",

    .long_name      = NULL_IF_CONFIG_SMALL("Discworld II BMV video"),

    .type           = AVMEDIA_TYPE_VIDEO,

    .id             = AV_CODEC_ID_BMV_VIDEO,

    .priv_data_size = sizeof(BMVDecContext),

    .init           = decode_init,

    .decode         = decode_frame,

    .capabilities   = AV_CODEC_CAP_DR1,

};