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/*

 * Microsoft Screen 3 (aka Microsoft ATC Screen) decoder

 * Copyright (c) 2012 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

 */

/**

 * @file

 * Microsoft Screen 3 (aka Microsoft ATC Screen) decoder

 */

#include "avcodec.h"

#include "bytestream.h"

#include "dsputil.h"

#include "internal.h"

#include "mss34dsp.h"

#define HEADER_SIZE 27

#define MODEL2_SCALE       13

#define MODEL_SCALE        15

#define MODEL256_SEC_SCALE  9

typedef struct Model2 {

    int      upd_val, till_rescale;

    unsigned zero_freq,  zero_weight;

    unsigned total_freq, total_weight;

} Model2;

typedef struct Model {

    int weights[16], freqs[16];

    int num_syms;

    int tot_weight;

    int upd_val, max_upd_val, till_rescale;

} Model;

typedef struct Model256 {

    int weights[256], freqs[256];

    int tot_weight;

    int secondary[68];

    int sec_size;

    int upd_val, max_upd_val, till_rescale;

} Model256;

#define RAC_BOTTOM 0x01000000

typedef struct RangeCoder {

    const uint8_t *src, *src_end;

    uint32_t range, low;

    int got_error;

} RangeCoder;

enum BlockType {

    FILL_BLOCK = 0,

    IMAGE_BLOCK,

    DCT_BLOCK,

    HAAR_BLOCK,

    SKIP_BLOCK

};

typedef struct BlockTypeContext {

    int      last_type;

    Model    bt_model[5];

} BlockTypeContext;

typedef struct FillBlockCoder {

    int      fill_val;

    Model    coef_model;

} FillBlockCoder;

typedef struct ImageBlockCoder {

    Model256 esc_model, vec_entry_model;

    Model    vec_size_model;

    Model    vq_model[125];

} ImageBlockCoder;

typedef struct DCTBlockCoder {

    int      *prev_dc;

    int      prev_dc_stride;

    int      prev_dc_height;

    int      quality;

    uint16_t qmat[64];

    Model    dc_model;

    Model2   sign_model;

    Model256 ac_model;

} DCTBlockCoder;

typedef struct HaarBlockCoder {

    int      quality, scale;

    Model256 coef_model;

    Model    coef_hi_model;

} HaarBlockCoder;

typedef struct MSS3Context {

    AVCodecContext   *avctx;

    AVFrame          *pic;

    int              got_error;

    RangeCoder       coder;

    BlockTypeContext btype[3];

    FillBlockCoder   fill_coder[3];

    ImageBlockCoder  image_coder[3];

    DCTBlockCoder    dct_coder[3];

    HaarBlockCoder   haar_coder[3];

    int              dctblock[64];

    int              hblock[16 * 16];

} MSS3Context;

static void model2_reset(Model2 *m)

{

    m->zero_weight  = 1;

    m->total_weight = 2;

    m->zero_freq    = 0x1000;

    m->total_freq   = 0x2000;

    m->upd_val      = 4;

    m->till_rescale = 4;

}

static void model2_update(Model2 *m, int bit)

{

    unsigned scale;

    if (!bit)

        m->zero_weight++;

    m->till_rescale--;

    if (m->till_rescale)

        return;

    m->total_weight += m->upd_val;

    if (m->total_weight > 0x2000) {

        m->total_weight = (m->total_weight + 1) >> 1;

        m->zero_weight  = (m->zero_weight  + 1) >> 1;

        if (m->total_weight == m->zero_weight)

            m->total_weight = m->zero_weight + 1;

    }

    m->upd_val = m->upd_val * 5 >> 2;

    if (m->upd_val > 64)

        m->upd_val = 64;

    scale = 0x80000000u / m->total_weight;

    m->zero_freq    = m->zero_weight  * scale >> 18;

    m->total_freq   = m->total_weight * scale >> 18;

    m->till_rescale = m->upd_val;

}

static void model_update(Model *m, int val)

{

    int i, sum = 0;

    unsigned scale;

    m->weights[val]++;

    m->till_rescale--;

    if (m->till_rescale)

        return;

    m->tot_weight += m->upd_val;

    if (m->tot_weight > 0x8000) {

        m->tot_weight = 0;

        for (i = 0; i < m->num_syms; i++) {

            m->weights[i]  = (m->weights[i] + 1) >> 1;

            m->tot_weight +=  m->weights[i];

        }

    }

    scale = 0x80000000u / m->tot_weight;

    for (i = 0; i < m->num_syms; i++) {

        m->freqs[i] = sum * scale >> 16;

        sum += m->weights[i];

    }

    m->upd_val = m->upd_val * 5 >> 2;

    if (m->upd_val > m->max_upd_val)

        m->upd_val = m->max_upd_val;

    m->till_rescale = m->upd_val;

}

static void model_reset(Model *m)

{

    int i;

    m->tot_weight   = 0;

    for (i = 0; i < m->num_syms - 1; i++)

        m->weights[i] = 1;

    m->weights[m->num_syms - 1] = 0;

    m->upd_val      = m->num_syms;

    m->till_rescale = 1;

    model_update(m, m->num_syms - 1);

    m->till_rescale =

    m->upd_val      = (m->num_syms + 6) >> 1;

}

static av_cold void model_init(Model *m, int num_syms)

{

    m->num_syms    = num_syms;

    m->max_upd_val = 8 * num_syms + 48;

    model_reset(m);

}

static void model256_update(Model256 *m, int val)

{

    int i, sum = 0;

    unsigned scale;

    int send, sidx = 1;

    m->weights[val]++;

    m->till_rescale--;

    if (m->till_rescale)

        return;

    m->tot_weight += m->upd_val;

    if (m->tot_weight > 0x8000) {

        m->tot_weight = 0;

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

            m->weights[i]  = (m->weights[i] + 1) >> 1;

            m->tot_weight +=  m->weights[i];

        }

    }

    scale = 0x80000000u / m->tot_weight;

    m->secondary[0] = 0;

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

        m->freqs[i] = sum * scale >> 16;

        sum += m->weights[i];

        send = m->freqs[i] >> MODEL256_SEC_SCALE;

        while (sidx <= send)

            m->secondary[sidx++] = i - 1;

    }

    while (sidx < m->sec_size)

        m->secondary[sidx++] = 255;

    m->upd_val = m->upd_val * 5 >> 2;

    if (m->upd_val > m->max_upd_val)

        m->upd_val = m->max_upd_val;

    m->till_rescale = m->upd_val;

}

static void model256_reset(Model256 *m)

{

    int i;

    for (i = 0; i < 255; i++)

        m->weights[i] = 1;

    m->weights[255] = 0;

    m->tot_weight   = 0;

    m->upd_val      = 256;

    m->till_rescale = 1;

    model256_update(m, 255);

    m->till_rescale =

    m->upd_val      = (256 + 6) >> 1;

}

static av_cold void model256_init(Model256 *m)

{

    m->max_upd_val = 8 * 256 + 48;

    m->sec_size    = (1 << 6) + 2;

    model256_reset(m);

}

static void rac_init(RangeCoder *c, const uint8_t *src, int size)

{

    int i;

    c->src       = src;

    c->src_end   = src + size;

    c->low       = 0;

    for (i = 0; i < FFMIN(size, 4); i++)

        c->low = (c->low << 8) | *c->src++;

    c->range     = 0xFFFFFFFF;

    c->got_error = 0;

}

static void rac_normalise(RangeCoder *c)

{

    for (;;) {

        c->range <<= 8;

        c->low   <<= 8;

        if (c->src < c->src_end) {

            c->low |= *c->src++;

        } else if (!c->low) {

            c->got_error = 1;

            c->low = 1;

        }

        if (c->range >= RAC_BOTTOM)

            return;

    }

}

static int rac_get_bit(RangeCoder *c)

{

    int bit;

    c->range >>= 1;

    bit = (c->range <= c->low);

    if (bit)

        c->low -= c->range;

    if (c->range < RAC_BOTTOM)

        rac_normalise(c);

    return bit;

}

static int rac_get_bits(RangeCoder *c, int nbits)

{

    int val;

    c->range >>= nbits;

    val = c->low / c->range;

    c->low -= c->range * val;

    if (c->range < RAC_BOTTOM)

        rac_normalise(c);

    return val;

}

static int rac_get_model2_sym(RangeCoder *c, Model2 *m)

{

    int bit, helper;

    helper = m->zero_freq * (c->range >> MODEL2_SCALE);

    bit    = (c->low >= helper);

    if (bit) {

        c->low   -= helper;

        c->range -= helper;

    } else {

        c->range  = helper;

    }

    if (c->range < RAC_BOTTOM)

        rac_normalise(c);

    model2_update(m, bit);

    return bit;

}

static int rac_get_model_sym(RangeCoder *c, Model *m)

{

    int prob, prob2, helper, val;

    int end, end2;

    prob       = 0;

    prob2      = c->range;

    c->range >>= MODEL_SCALE;

    val        = 0;

    end        = m->num_syms >> 1;

    end2       = m->num_syms;

    do {

        helper = m->freqs[end] * c->range;

        if (helper <= c->low) {

            val   = end;

            prob  = helper;

        } else {

            end2  = end;

            prob2 = helper;

        }

        end = (end2 + val) >> 1;

    } while (end != val);

    c->low  -= prob;

    c->range = prob2 - prob;

    if (c->range < RAC_BOTTOM)

        rac_normalise(c);

    model_update(m, val);

    return val;

}

static int rac_get_model256_sym(RangeCoder *c, Model256 *m)

{

    int prob, prob2, helper, val;

    int start, end;

    int ssym;

    prob2      = c->range;

    c->range >>= MODEL_SCALE;

    helper     = c->low / c->range;

    ssym       = helper >> MODEL256_SEC_SCALE;

    val        = m->secondary[ssym];

    end = start = m->secondary[ssym + 1] + 1;

    while (end > val + 1) {

        ssym = (end + val) >> 1;

        if (m->freqs[ssym] <= helper) {

            end = start;

            val = ssym;

        } else {

            end   = (end + val) >> 1;

            start = ssym;

        }

    }

    prob = m->freqs[val] * c->range;

    if (val != 255)

        prob2 = m->freqs[val + 1] * c->range;

    c->low  -= prob;

    c->range = prob2 - prob;

    if (c->range < RAC_BOTTOM)

        rac_normalise(c);

    model256_update(m, val);

    return val;

}

static int decode_block_type(RangeCoder *c, BlockTypeContext *bt)

{

    bt->last_type = rac_get_model_sym(c, &bt->bt_model[bt->last_type]);

    return bt->last_type;

}

static int decode_coeff(RangeCoder *c, Model *m)

{

    int val, sign;

    val = rac_get_model_sym(c, m);

    if (val) {

        sign = rac_get_bit(c);

        if (val > 1) {

            val--;

            val = (1 << val) + rac_get_bits(c, val);

        }

        if (!sign)

            val = -val;

    }

    return val;

}

static void decode_fill_block(RangeCoder *c, FillBlockCoder *fc,

                              uint8_t *dst, int stride, int block_size)

{

    int i;

    fc->fill_val += decode_coeff(c, &fc->coef_model);

    for (i = 0; i < block_size; i++, dst += stride)

        memset(dst, fc->fill_val, block_size);

}

static void decode_image_block(RangeCoder *c, ImageBlockCoder *ic,

                               uint8_t *dst, int stride, int block_size)

{

    int i, j;

    int vec_size;

    int vec[4];

    int prev_line[16];

    int A, B, C;

    vec_size = rac_get_model_sym(c, &ic->vec_size_model) + 2;

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

        vec[i] = rac_get_model256_sym(c, &ic->vec_entry_model);

    for (; i < 4; i++)

        vec[i] = 0;

    memset(prev_line, 0, sizeof(prev_line));

    for (j = 0; j < block_size; j++) {

        A = 0;

        B = 0;

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

            C = B;

            B = prev_line[i];

            A = rac_get_model_sym(c, &ic->vq_model[A + B * 5 + C * 25]);

            prev_line[i] = A;

            if (A < 4)

               dst[i] = vec[A];

            else

               dst[i] = rac_get_model256_sym(c, &ic->esc_model);

        }

        dst += stride;

    }

}

static int decode_dct(RangeCoder *c, DCTBlockCoder *bc, int *block,

                      int bx, int by)

{

    int skip, val, sign, pos = 1, zz_pos, dc;

    int blk_pos = bx + by * bc->prev_dc_stride;

    memset(block, 0, sizeof(*block) * 64);

    dc = decode_coeff(c, &bc->dc_model);

    if (by) {

        if (bx) {

            int l, tl, t;

            l  = bc->prev_dc[blk_pos - 1];

            tl = bc->prev_dc[blk_pos - 1 - bc->prev_dc_stride];

            t  = bc->prev_dc[blk_pos     - bc->prev_dc_stride];

            if (FFABS(t - tl) <= FFABS(l - tl))

                dc += l;

            else

                dc += t;

        } else {

            dc += bc->prev_dc[blk_pos - bc->prev_dc_stride];

        }

    } else if (bx) {

        dc += bc->prev_dc[bx - 1];

    }

    bc->prev_dc[blk_pos] = dc;

    block[0]             = dc * bc->qmat[0];

    while (pos < 64) {

        val = rac_get_model256_sym(c, &bc->ac_model);

        if (!val)

            return 0;

        if (val == 0xF0) {

            pos += 16;

            continue;

        }

        skip = val >> 4;

        val  = val & 0xF;

        if (!val)

            return -1;

        pos += skip;

        if (pos >= 64)

            return -1;

        sign = rac_get_model2_sym(c, &bc->sign_model);

        if (val > 1) {

            val--;

            val = (1 << val) + rac_get_bits(c, val);

        }

        if (!sign)

            val = -val;

        zz_pos = ff_zigzag_direct[pos];

        block[zz_pos] = val * bc->qmat[zz_pos];

        pos++;

    }

    return pos == 64 ? 0 : -1;

}

static void decode_dct_block(RangeCoder *c, DCTBlockCoder *bc,

                             uint8_t *dst, int stride, int block_size,

                             int *block, int mb_x, int mb_y)

{

    int i, j;

    int bx, by;

    int nblocks = block_size >> 3;

    bx = mb_x * nblocks;

    by = mb_y * nblocks;

    for (j = 0; j < nblocks; j++) {

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

            if (decode_dct(c, bc, block, bx + i, by + j)) {

                c->got_error = 1;

                return;

            }

            ff_mss34_dct_put(dst + i * 8, stride, block);

        }

        dst += 8 * stride;

    }

}

static void decode_haar_block(RangeCoder *c, HaarBlockCoder *hc,

                              uint8_t *dst, int stride, int block_size,

                              int *block)

{

    const int hsize = block_size >> 1;

    int A, B, C, D, t1, t2, t3, t4;

    int i, j;

    for (j = 0; j < block_size; j++) {

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

            if (i < hsize && j < hsize)

                block[i] = rac_get_model256_sym(c, &hc->coef_model);

            else

                block[i] = decode_coeff(c, &hc->coef_hi_model);

            block[i] *= hc->scale;

        }

        block += block_size;

    }

    block -= block_size * block_size;

    for (j = 0; j < hsize; j++) {

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

            A = block[i];

            B = block[i + hsize];

            C = block[i + hsize * block_size];

            D = block[i + hsize * block_size + hsize];

            t1 = A - B;

            t2 = C - D;

            t3 = A + B;

            t4 = C + D;

            dst[i * 2]              = av_clip_uint8(t1 - t2);

            dst[i * 2 + stride]     = av_clip_uint8(t1 + t2);

            dst[i * 2 + 1]          = av_clip_uint8(t3 - t4);

            dst[i * 2 + 1 + stride] = av_clip_uint8(t3 + t4);

        }

        block += block_size;

        dst   += stride * 2;

    }

}

static void reset_coders(MSS3Context *ctx, int quality)

{

    int i, j;

    for (i = 0; i < 3; i++) {

        ctx->btype[i].last_type = SKIP_BLOCK;

        for (j = 0; j < 5; j++)

            model_reset(&ctx->btype[i].bt_model[j]);

        ctx->fill_coder[i].fill_val = 0;

        model_reset(&ctx->fill_coder[i].coef_model);

        model256_reset(&ctx->image_coder[i].esc_model);

        model256_reset(&ctx->image_coder[i].vec_entry_model);

        model_reset(&ctx->image_coder[i].vec_size_model);

        for (j = 0; j < 125; j++)

            model_reset(&ctx->image_coder[i].vq_model[j]);

        if (ctx->dct_coder[i].quality != quality) {

            ctx->dct_coder[i].quality = quality;

            ff_mss34_gen_quant_mat(ctx->dct_coder[i].qmat, quality, !i);

        }

        memset(ctx->dct_coder[i].prev_dc, 0,

               sizeof(*ctx->dct_coder[i].prev_dc) *

               ctx->dct_coder[i].prev_dc_stride *

               ctx->dct_coder[i].prev_dc_height);

        model_reset(&ctx->dct_coder[i].dc_model);

        model2_reset(&ctx->dct_coder[i].sign_model);

        model256_reset(&ctx->dct_coder[i].ac_model);

        if (ctx->haar_coder[i].quality != quality) {

            ctx->haar_coder[i].quality = quality;

            ctx->haar_coder[i].scale   = 17 - 7 * quality / 50;

        }

        model_reset(&ctx->haar_coder[i].coef_hi_model);

        model256_reset(&ctx->haar_coder[i].coef_model);

    }

}

static av_cold void init_coders(MSS3Context *ctx)

{

    int i, j;

    for (i = 0; i < 3; i++) {

        for (j = 0; j < 5; j++)

            model_init(&ctx->btype[i].bt_model[j], 5);

        model_init(&ctx->fill_coder[i].coef_model, 12);

        model256_init(&ctx->image_coder[i].esc_model);

        model256_init(&ctx->image_coder[i].vec_entry_model);

        model_init(&ctx->image_coder[i].vec_size_model, 3);

        for (j = 0; j < 125; j++)

            model_init(&ctx->image_coder[i].vq_model[j], 5);

        model_init(&ctx->dct_coder[i].dc_model, 12);

        model256_init(&ctx->dct_coder[i].ac_model);

        model_init(&ctx->haar_coder[i].coef_hi_model, 12);

        model256_init(&ctx->haar_coder[i].coef_model);

    }

}

static int mss3_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,

                             AVPacket *avpkt)

{

    const uint8_t *buf = avpkt->data;

    int buf_size = avpkt->size;

    MSS3Context *c = avctx->priv_data;

    RangeCoder *acoder = &c->coder;

    GetByteContext gb;

    uint8_t *dst[3];

    int dec_width, dec_height, dec_x, dec_y, quality, keyframe;

    int x, y, i, mb_width, mb_height, blk_size, btype;

    int ret;

    if (buf_size < HEADER_SIZE) {

        av_log(avctx, AV_LOG_ERROR,

               "Frame should have at least %d bytes, got %d instead\n",

               HEADER_SIZE, buf_size);

        return AVERROR_INVALIDDATA;

    }

    bytestream2_init(&gb, buf, buf_size);

    keyframe   = bytestream2_get_be32(&gb);

    if (keyframe & ~0x301) {

        av_log(avctx, AV_LOG_ERROR, "Invalid frame type %X\n", keyframe);

        return AVERROR_INVALIDDATA;

    }

    keyframe   = !(keyframe & 1);

    bytestream2_skip(&gb, 6);

    dec_x      = bytestream2_get_be16(&gb);

    dec_y      = bytestream2_get_be16(&gb);

    dec_width  = bytestream2_get_be16(&gb);

    dec_height = bytestream2_get_be16(&gb);

    if (dec_x + dec_width > avctx->width ||

        dec_y + dec_height > avctx->height ||

        (dec_width | dec_height) & 0xF) {

        av_log(avctx, AV_LOG_ERROR, "Invalid frame dimensions %dx%d +%d,%d\n",

               dec_width, dec_height, dec_x, dec_y);

        return AVERROR_INVALIDDATA;

    }

    bytestream2_skip(&gb, 4);

    quality    = bytestream2_get_byte(&gb);

    if (quality < 1 || quality > 100) {

        av_log(avctx, AV_LOG_ERROR, "Invalid quality setting %d\n", quality);

        return AVERROR_INVALIDDATA;

    }

    bytestream2_skip(&gb, 4);

    if (keyframe && !bytestream2_get_bytes_left(&gb)) {

        av_log(avctx, AV_LOG_ERROR, "Keyframe without data found\n");

        return AVERROR_INVALIDDATA;

    }

    if (!keyframe && c->got_error)

        return buf_size;

    c->got_error = 0;

    if ((ret = ff_reget_buffer(avctx, c->pic)) < 0)

        return ret;

    c->pic->key_frame = keyframe;

    c->pic->pict_type = keyframe ? AV_PICTURE_TYPE_I : AV_PICTURE_TYPE_P;

    if (!bytestream2_get_bytes_left(&gb)) {

        if ((ret = av_frame_ref(data, c->pic)) < 0)

            return ret;

        *got_frame      = 1;

        return buf_size;

    }

    reset_coders(c, quality);

    rac_init(acoder, buf + HEADER_SIZE, buf_size - HEADER_SIZE);

    mb_width  = dec_width  >> 4;

    mb_height = dec_height >> 4;

    dst[0] = c->pic->data[0] + dec_x     +  dec_y      * c->pic->linesize[0];

    dst[1] = c->pic->data[1] + dec_x / 2 + (dec_y / 2) * c->pic->linesize[1];

    dst[2] = c->pic->data[2] + dec_x / 2 + (dec_y / 2) * c->pic->linesize[2];

    for (y = 0; y < mb_height; y++) {

        for (x = 0; x < mb_width; x++) {

            for (i = 0; i < 3; i++) {

                blk_size = 8 << !i;

                btype = decode_block_type(acoder, c->btype + i);

                switch (btype) {

                case FILL_BLOCK:

                    decode_fill_block(acoder, c->fill_coder + i,

                                      dst[i] + x * blk_size,

                                      c->pic->linesize[i], blk_size);

                    break;

                case IMAGE_BLOCK:

                    decode_image_block(acoder, c->image_coder + i,

                                       dst[i] + x * blk_size,

                                       c->pic->linesize[i], blk_size);

                    break;

                case DCT_BLOCK:

                    decode_dct_block(acoder, c->dct_coder + i,

                                     dst[i] + x * blk_size,

                                     c->pic->linesize[i], blk_size,

                                     c->dctblock, x, y);

                    break;

                case HAAR_BLOCK:

                    decode_haar_block(acoder, c->haar_coder + i,

                                      dst[i] + x * blk_size,

                                      c->pic->linesize[i], blk_size,

                                      c->hblock);

                    break;

                }

                if (c->got_error || acoder->got_error) {

                    av_log(avctx, AV_LOG_ERROR, "Error decoding block %d,%d\n",

                           x, y);

                    c->got_error = 1;

                    return AVERROR_INVALIDDATA;

                }

            }

        }

        dst[0] += c->pic->linesize[0] * 16;

        dst[1] += c->pic->linesize[1] * 8;

        dst[2] += c->pic->linesize[2] * 8;

    }

    if ((ret = av_frame_ref(data, c->pic)) < 0)

        return ret;

    *got_frame      = 1;

    return buf_size;

}

static av_cold int mss3_decode_init(AVCodecContext *avctx)

{

    MSS3Context * const c = avctx->priv_data;

    int i;

    c->avctx = avctx;

    c->pic = av_frame_alloc();

    if (!c->pic)

        return AVERROR(ENOMEM);

    if ((avctx->width & 0xF) || (avctx->height & 0xF)) {

        av_log(avctx, AV_LOG_ERROR,

               "Image dimensions should be a multiple of 16.\n");

        return AVERROR_INVALIDDATA;

    }

    c->got_error = 0;

    for (i = 0; i < 3; i++) {

        int b_width  = avctx->width  >> (2 + !!i);

        int b_height = avctx->height >> (2 + !!i);

        c->dct_coder[i].prev_dc_stride = b_width;

        c->dct_coder[i].prev_dc_height = b_height;

        c->dct_coder[i].prev_dc = av_malloc(sizeof(*c->dct_coder[i].prev_dc) *

                                            b_width * b_height);

        if (!c->dct_coder[i].prev_dc) {

            av_log(avctx, AV_LOG_ERROR, "Cannot allocate buffer\n");

            av_frame_free(&c->pic);

            while (i >= 0) {

                av_freep(&c->dct_coder[i].prev_dc);

                i--;

            }

            return AVERROR(ENOMEM);

        }

    }

    avctx->pix_fmt     = AV_PIX_FMT_YUV420P;

    init_coders(c);

    return 0;

}

static av_cold int mss3_decode_end(AVCodecContext *avctx)

{

    MSS3Context * const c = avctx->priv_data;

    int i;

    av_frame_free(&c->pic);

    for (i = 0; i < 3; i++)

        av_freep(&c->dct_coder[i].prev_dc);

    return 0;

}

AVCodec ff_msa1_decoder = {

    .name           = "msa1",

    .long_name      = NULL_IF_CONFIG_SMALL("MS ATC Screen"),

    .type           = AVMEDIA_TYPE_VIDEO,

    .id             = AV_CODEC_ID_MSA1,

    .priv_data_size = sizeof(MSS3Context),

    .init           = mss3_decode_init,

    .close          = mss3_decode_end,

    .decode         = mss3_decode_frame,

    .capabilities   = CODEC_CAP_DR1,

};