1/*
2 * Escape 124 Video Decoder
3 * Copyright (C) 2008 Eli Friedman (eli.friedman@gmail.com)
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22#include "avcodec.h"
23
24#define ALT_BITSTREAM_READER_LE
25#include "get_bits.h"
26
27typedef union MacroBlock {
28    uint16_t pixels[4];
29    uint32_t pixels32[2];
30} MacroBlock;
31
32typedef union SuperBlock {
33    uint16_t pixels[64];
34    uint32_t pixels32[32];
35} SuperBlock;
36
37typedef struct CodeBook {
38    unsigned depth;
39    unsigned size;
40    MacroBlock* blocks;
41} CodeBook;
42
43typedef struct Escape124Context {
44    AVFrame frame;
45
46    unsigned num_superblocks;
47
48    CodeBook codebooks[3];
49} Escape124Context;
50
51static int can_safely_read(GetBitContext* gb, int bits) {
52    return get_bits_count(gb) + bits <= gb->size_in_bits;
53}
54
55/**
56 * Initialize the decoder
57 * @param avctx decoder context
58 * @return 0 success, negative on error
59 */
60static av_cold int escape124_decode_init(AVCodecContext *avctx)
61{
62    Escape124Context *s = avctx->priv_data;
63
64    avctx->pix_fmt = PIX_FMT_RGB555;
65
66    s->num_superblocks = ((unsigned)avctx->width / 8) *
67                         ((unsigned)avctx->height / 8);
68
69    return 0;
70}
71
72static av_cold int escape124_decode_close(AVCodecContext *avctx)
73{
74    unsigned i;
75    Escape124Context *s = avctx->priv_data;
76
77    for (i = 0; i < 3; i++)
78        av_free(s->codebooks[i].blocks);
79
80    if (s->frame.data[0])
81        avctx->release_buffer(avctx, &s->frame);
82
83    return 0;
84}
85
86static CodeBook unpack_codebook(GetBitContext* gb, unsigned depth,
87                                 unsigned size)
88{
89    unsigned i, j;
90    CodeBook cb = { 0 };
91
92    if (!can_safely_read(gb, size * 34))
93        return cb;
94
95    if (size >= INT_MAX / sizeof(MacroBlock))
96        return cb;
97    cb.blocks = av_malloc(size ? size * sizeof(MacroBlock) : 1);
98    if (!cb.blocks)
99        return cb;
100
101    cb.depth = depth;
102    cb.size = size;
103    for (i = 0; i < size; i++) {
104        unsigned mask_bits = get_bits(gb, 4);
105        unsigned color0 = get_bits(gb, 15);
106        unsigned color1 = get_bits(gb, 15);
107
108        for (j = 0; j < 4; j++) {
109            if (mask_bits & (1 << j))
110                cb.blocks[i].pixels[j] = color1;
111            else
112                cb.blocks[i].pixels[j] = color0;
113        }
114    }
115    return cb;
116}
117
118static unsigned decode_skip_count(GetBitContext* gb)
119{
120    unsigned value;
121    // This function reads a maximum of 23 bits,
122    // which is within the padding space
123    if (!can_safely_read(gb, 1))
124        return -1;
125    value = get_bits1(gb);
126    if (!value)
127        return value;
128
129    value += get_bits(gb, 3);
130    if (value != (1 + ((1 << 3) - 1)))
131        return value;
132
133    value += get_bits(gb, 7);
134    if (value != (1 + ((1 << 3) - 1)) + ((1 << 7) - 1))
135        return value;
136
137    return value + get_bits(gb, 12);
138}
139
140static MacroBlock decode_macroblock(Escape124Context* s, GetBitContext* gb,
141                                    int* codebook_index, int superblock_index)
142{
143    // This function reads a maximum of 22 bits; the callers
144    // guard this function appropriately
145    unsigned block_index, depth;
146
147    if (get_bits1(gb)) {
148        static const char transitions[3][2] = { {2, 1}, {0, 2}, {1, 0} };
149        *codebook_index = transitions[*codebook_index][get_bits1(gb)];
150    }
151
152    depth = s->codebooks[*codebook_index].depth;
153
154    // depth = 0 means that this shouldn't read any bits;
155    // in theory, this is the same as get_bits(gb, 0), but
156    // that doesn't actually work.
157    block_index = depth ? get_bits(gb, depth) : 0;
158
159    if (*codebook_index == 1) {
160        block_index += superblock_index << s->codebooks[1].depth;
161    }
162
163    // This condition can occur with invalid bitstreams and
164    // *codebook_index == 2
165    if (block_index >= s->codebooks[*codebook_index].size)
166        return (MacroBlock) { { 0 } };
167
168    return s->codebooks[*codebook_index].blocks[block_index];
169}
170
171static void insert_mb_into_sb(SuperBlock* sb, MacroBlock mb, unsigned index) {
172   // Formula: ((index / 4) * 16 + (index % 4) * 2) / 2
173   uint32_t *dst = sb->pixels32 + index + (index & -4);
174
175   // This technically violates C99 aliasing rules, but it should be safe.
176   dst[0] = mb.pixels32[0];
177   dst[4] = mb.pixels32[1];
178}
179
180static void copy_superblock(uint16_t* dest, unsigned dest_stride,
181                            uint16_t* src, unsigned src_stride)
182{
183    unsigned y;
184    if (src)
185        for (y = 0; y < 8; y++)
186            memcpy(dest + y * dest_stride, src + y * src_stride,
187                   sizeof(uint16_t) * 8);
188    else
189        for (y = 0; y < 8; y++)
190            memset(dest + y * dest_stride, 0, sizeof(uint16_t) * 8);
191}
192
193static const uint16_t mask_matrix[] = {0x1,   0x2,   0x10,   0x20,
194                                       0x4,   0x8,   0x40,   0x80,
195                                       0x100, 0x200, 0x1000, 0x2000,
196                                       0x400, 0x800, 0x4000, 0x8000};
197
198/**
199 * Decode a single frame
200 * @param avctx decoder context
201 * @param data decoded frame
202 * @param data_size size of the decoded frame
203 * @param buf input buffer
204 * @param buf_size input buffer size
205 * @return 0 success, -1 on error
206 */
207static int escape124_decode_frame(AVCodecContext *avctx,
208                                  void *data, int *data_size,
209                                  AVPacket *avpkt)
210{
211    const uint8_t *buf = avpkt->data;
212    int buf_size = avpkt->size;
213    Escape124Context *s = avctx->priv_data;
214
215    GetBitContext gb;
216    unsigned frame_flags, frame_size;
217    unsigned i;
218
219    unsigned superblock_index, cb_index = 1,
220             superblock_col_index = 0,
221             superblocks_per_row = avctx->width / 8, skip = -1;
222
223    uint16_t* old_frame_data, *new_frame_data;
224    unsigned old_stride, new_stride;
225
226    AVFrame new_frame = { { 0 } };
227
228    init_get_bits(&gb, buf, buf_size * 8);
229
230    // This call also guards the potential depth reads for the
231    // codebook unpacking.
232    if (!can_safely_read(&gb, 64))
233        return -1;
234
235    frame_flags = get_bits_long(&gb, 32);
236    frame_size  = get_bits_long(&gb, 32);
237
238    // Leave last frame unchanged
239    // FIXME: Is this necessary?  I haven't seen it in any real samples
240    if (!(frame_flags & 0x114) || !(frame_flags & 0x7800000)) {
241        av_log(NULL, AV_LOG_DEBUG, "Skipping frame\n");
242
243        *data_size = sizeof(AVFrame);
244        *(AVFrame*)data = s->frame;
245
246        return frame_size;
247    }
248
249    for (i = 0; i < 3; i++) {
250        if (frame_flags & (1 << (17 + i))) {
251            unsigned cb_depth, cb_size;
252            if (i == 2) {
253                // This codebook can be cut off at places other than
254                // powers of 2, leaving some of the entries undefined.
255                cb_size = get_bits_long(&gb, 20);
256                cb_depth = av_log2(cb_size - 1) + 1;
257            } else {
258                cb_depth = get_bits(&gb, 4);
259                if (i == 0) {
260                    // This is the most basic codebook: pow(2,depth) entries
261                    // for a depth-length key
262                    cb_size = 1 << cb_depth;
263                } else {
264                    // This codebook varies per superblock
265                    // FIXME: I don't think this handles integer overflow
266                    // properly
267                    cb_size = s->num_superblocks << cb_depth;
268                }
269            }
270            av_free(s->codebooks[i].blocks);
271            s->codebooks[i] = unpack_codebook(&gb, cb_depth, cb_size);
272            if (!s->codebooks[i].blocks)
273                return -1;
274        }
275    }
276
277    new_frame.reference = 3;
278    if (avctx->get_buffer(avctx, &new_frame)) {
279        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
280        return -1;
281    }
282
283    new_frame_data = (uint16_t*)new_frame.data[0];
284    new_stride = new_frame.linesize[0] / 2;
285    old_frame_data = (uint16_t*)s->frame.data[0];
286    old_stride = s->frame.linesize[0] / 2;
287
288    for (superblock_index = 0; superblock_index < s->num_superblocks;
289         superblock_index++) {
290        MacroBlock mb;
291        SuperBlock sb;
292        unsigned multi_mask = 0;
293
294        if (skip == -1) {
295            // Note that this call will make us skip the rest of the blocks
296            // if the frame prematurely ends
297            skip = decode_skip_count(&gb);
298        }
299
300        if (skip) {
301            copy_superblock(new_frame_data, new_stride,
302                            old_frame_data, old_stride);
303        } else {
304            copy_superblock(sb.pixels, 8,
305                            old_frame_data, old_stride);
306
307            while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
308                unsigned mask;
309                mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
310                mask = get_bits(&gb, 16);
311                multi_mask |= mask;
312                for (i = 0; i < 16; i++) {
313                    if (mask & mask_matrix[i]) {
314                        insert_mb_into_sb(&sb, mb, i);
315                    }
316                }
317            }
318
319            if (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
320                unsigned inv_mask = get_bits(&gb, 4);
321                for (i = 0; i < 4; i++) {
322                    if (inv_mask & (1 << i)) {
323                        multi_mask ^= 0xF << i*4;
324                    } else {
325                        multi_mask ^= get_bits(&gb, 4) << i*4;
326                    }
327                }
328
329                for (i = 0; i < 16; i++) {
330                    if (multi_mask & mask_matrix[i]) {
331                        if (!can_safely_read(&gb, 1))
332                            break;
333                        mb = decode_macroblock(s, &gb, &cb_index,
334                                               superblock_index);
335                        insert_mb_into_sb(&sb, mb, i);
336                    }
337                }
338            } else if (frame_flags & (1 << 16)) {
339                while (can_safely_read(&gb, 1) && !get_bits1(&gb)) {
340                    mb = decode_macroblock(s, &gb, &cb_index, superblock_index);
341                    insert_mb_into_sb(&sb, mb, get_bits(&gb, 4));
342                }
343            }
344
345            copy_superblock(new_frame_data, new_stride, sb.pixels, 8);
346        }
347
348        superblock_col_index++;
349        new_frame_data += 8;
350        if (old_frame_data)
351            old_frame_data += 8;
352        if (superblock_col_index == superblocks_per_row) {
353            new_frame_data += new_stride * 8 - superblocks_per_row * 8;
354            if (old_frame_data)
355                old_frame_data += old_stride * 8 - superblocks_per_row * 8;
356            superblock_col_index = 0;
357        }
358        skip--;
359    }
360
361    av_log(NULL, AV_LOG_DEBUG,
362           "Escape sizes: %i, %i, %i\n",
363           frame_size, buf_size, get_bits_count(&gb) / 8);
364
365    if (s->frame.data[0])
366        avctx->release_buffer(avctx, &s->frame);
367
368    *(AVFrame*)data = s->frame = new_frame;
369    *data_size = sizeof(AVFrame);
370
371    return frame_size;
372}
373
374
375AVCodec escape124_decoder = {
376    "escape124",
377    AVMEDIA_TYPE_VIDEO,
378    CODEC_ID_ESCAPE124,
379    sizeof(Escape124Context),
380    escape124_decode_init,
381    NULL,
382    escape124_decode_close,
383    escape124_decode_frame,
384    CODEC_CAP_DR1,
385    .long_name = NULL_IF_CONFIG_SMALL("Escape 124"),
386};
387
388