summaryrefslogtreecommitdiffstats
path: root/media/libwebp/dec/vp8l_dec.c
blob: 6af696ddccf3a7164ab2677d73488ab372a10e80 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
// Copyright 2012 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// main entry for the decoder
//
// Authors: Vikas Arora (vikaas.arora@gmail.com)
//          Jyrki Alakuijala (jyrki@google.com)

#include <stdlib.h>

#include "../dec/alphai_dec.h"
#include "../dec/vp8li_dec.h"
#include "../dsp/dsp.h"
#include "../dsp/lossless.h"
#include "../dsp/lossless_common.h"
#include "../dsp/yuv.h"
#include "../utils/endian_inl_utils.h"
#include "../utils/huffman_utils.h"
#include "../utils/utils.h"

#define NUM_ARGB_CACHE_ROWS          16

static const int kCodeLengthLiterals = 16;
static const int kCodeLengthRepeatCode = 16;
static const uint8_t kCodeLengthExtraBits[3] = { 2, 3, 7 };
static const uint8_t kCodeLengthRepeatOffsets[3] = { 3, 3, 11 };

// -----------------------------------------------------------------------------
//  Five Huffman codes are used at each meta code:
//  1. green + length prefix codes + color cache codes,
//  2. alpha,
//  3. red,
//  4. blue, and,
//  5. distance prefix codes.
typedef enum {
  GREEN = 0,
  RED   = 1,
  BLUE  = 2,
  ALPHA = 3,
  DIST  = 4
} HuffIndex;

static const uint16_t kAlphabetSize[HUFFMAN_CODES_PER_META_CODE] = {
  NUM_LITERAL_CODES + NUM_LENGTH_CODES,
  NUM_LITERAL_CODES, NUM_LITERAL_CODES, NUM_LITERAL_CODES,
  NUM_DISTANCE_CODES
};

static const uint8_t kLiteralMap[HUFFMAN_CODES_PER_META_CODE] = {
  0, 1, 1, 1, 0
};

#define NUM_CODE_LENGTH_CODES       19
static const uint8_t kCodeLengthCodeOrder[NUM_CODE_LENGTH_CODES] = {
  17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
};

#define CODE_TO_PLANE_CODES        120
static const uint8_t kCodeToPlane[CODE_TO_PLANE_CODES] = {
  0x18, 0x07, 0x17, 0x19, 0x28, 0x06, 0x27, 0x29, 0x16, 0x1a,
  0x26, 0x2a, 0x38, 0x05, 0x37, 0x39, 0x15, 0x1b, 0x36, 0x3a,
  0x25, 0x2b, 0x48, 0x04, 0x47, 0x49, 0x14, 0x1c, 0x35, 0x3b,
  0x46, 0x4a, 0x24, 0x2c, 0x58, 0x45, 0x4b, 0x34, 0x3c, 0x03,
  0x57, 0x59, 0x13, 0x1d, 0x56, 0x5a, 0x23, 0x2d, 0x44, 0x4c,
  0x55, 0x5b, 0x33, 0x3d, 0x68, 0x02, 0x67, 0x69, 0x12, 0x1e,
  0x66, 0x6a, 0x22, 0x2e, 0x54, 0x5c, 0x43, 0x4d, 0x65, 0x6b,
  0x32, 0x3e, 0x78, 0x01, 0x77, 0x79, 0x53, 0x5d, 0x11, 0x1f,
  0x64, 0x6c, 0x42, 0x4e, 0x76, 0x7a, 0x21, 0x2f, 0x75, 0x7b,
  0x31, 0x3f, 0x63, 0x6d, 0x52, 0x5e, 0x00, 0x74, 0x7c, 0x41,
  0x4f, 0x10, 0x20, 0x62, 0x6e, 0x30, 0x73, 0x7d, 0x51, 0x5f,
  0x40, 0x72, 0x7e, 0x61, 0x6f, 0x50, 0x71, 0x7f, 0x60, 0x70
};

// Memory needed for lookup tables of one Huffman tree group. Red, blue, alpha
// and distance alphabets are constant (256 for red, blue and alpha, 40 for
// distance) and lookup table sizes for them in worst case are 630 and 410
// respectively. Size of green alphabet depends on color cache size and is equal
// to 256 (green component values) + 24 (length prefix values)
// + color_cache_size (between 0 and 2048).
// All values computed for 8-bit first level lookup with Mark Adler's tool:
// http://www.hdfgroup.org/ftp/lib-external/zlib/zlib-1.2.5/examples/enough.c
#define FIXED_TABLE_SIZE (630 * 3 + 410)
static const uint16_t kTableSize[12] = {
  FIXED_TABLE_SIZE + 654,
  FIXED_TABLE_SIZE + 656,
  FIXED_TABLE_SIZE + 658,
  FIXED_TABLE_SIZE + 662,
  FIXED_TABLE_SIZE + 670,
  FIXED_TABLE_SIZE + 686,
  FIXED_TABLE_SIZE + 718,
  FIXED_TABLE_SIZE + 782,
  FIXED_TABLE_SIZE + 912,
  FIXED_TABLE_SIZE + 1168,
  FIXED_TABLE_SIZE + 1680,
  FIXED_TABLE_SIZE + 2704
};

static int DecodeImageStream(int xsize, int ysize,
                             int is_level0,
                             VP8LDecoder* const dec,
                             uint32_t** const decoded_data);

//------------------------------------------------------------------------------

int VP8LCheckSignature(const uint8_t* const data, size_t size) {
  return (size >= VP8L_FRAME_HEADER_SIZE &&
          data[0] == VP8L_MAGIC_BYTE &&
          (data[4] >> 5) == 0);  // version
}

static int ReadImageInfo(VP8LBitReader* const br,
                         int* const width, int* const height,
                         int* const has_alpha) {
  if (VP8LReadBits(br, 8) != VP8L_MAGIC_BYTE) return 0;
  *width = VP8LReadBits(br, VP8L_IMAGE_SIZE_BITS) + 1;
  *height = VP8LReadBits(br, VP8L_IMAGE_SIZE_BITS) + 1;
  *has_alpha = VP8LReadBits(br, 1);
  if (VP8LReadBits(br, VP8L_VERSION_BITS) != 0) return 0;
  return !br->eos_;
}

int VP8LGetInfo(const uint8_t* data, size_t data_size,
                int* const width, int* const height, int* const has_alpha) {
  if (data == NULL || data_size < VP8L_FRAME_HEADER_SIZE) {
    return 0;         // not enough data
  } else if (!VP8LCheckSignature(data, data_size)) {
    return 0;         // bad signature
  } else {
    int w, h, a;
    VP8LBitReader br;
    VP8LInitBitReader(&br, data, data_size);
    if (!ReadImageInfo(&br, &w, &h, &a)) {
      return 0;
    }
    if (width != NULL) *width = w;
    if (height != NULL) *height = h;
    if (has_alpha != NULL) *has_alpha = a;
    return 1;
  }
}

//------------------------------------------------------------------------------

static WEBP_INLINE int GetCopyDistance(int distance_symbol,
                                       VP8LBitReader* const br) {
  int extra_bits, offset;
  if (distance_symbol < 4) {
    return distance_symbol + 1;
  }
  extra_bits = (distance_symbol - 2) >> 1;
  offset = (2 + (distance_symbol & 1)) << extra_bits;
  return offset + VP8LReadBits(br, extra_bits) + 1;
}

static WEBP_INLINE int GetCopyLength(int length_symbol,
                                     VP8LBitReader* const br) {
  // Length and distance prefixes are encoded the same way.
  return GetCopyDistance(length_symbol, br);
}

static WEBP_INLINE int PlaneCodeToDistance(int xsize, int plane_code) {
  if (plane_code > CODE_TO_PLANE_CODES) {
    return plane_code - CODE_TO_PLANE_CODES;
  } else {
    const int dist_code = kCodeToPlane[plane_code - 1];
    const int yoffset = dist_code >> 4;
    const int xoffset = 8 - (dist_code & 0xf);
    const int dist = yoffset * xsize + xoffset;
    return (dist >= 1) ? dist : 1;  // dist<1 can happen if xsize is very small
  }
}

//------------------------------------------------------------------------------
// Decodes the next Huffman code from bit-stream.
// FillBitWindow(br) needs to be called at minimum every second call
// to ReadSymbol, in order to pre-fetch enough bits.
static WEBP_INLINE int ReadSymbol(const HuffmanCode* table,
                                  VP8LBitReader* const br) {
  int nbits;
  uint32_t val = VP8LPrefetchBits(br);
  table += val & HUFFMAN_TABLE_MASK;
  nbits = table->bits - HUFFMAN_TABLE_BITS;
  if (nbits > 0) {
    VP8LSetBitPos(br, br->bit_pos_ + HUFFMAN_TABLE_BITS);
    val = VP8LPrefetchBits(br);
    table += table->value;
    table += val & ((1 << nbits) - 1);
  }
  VP8LSetBitPos(br, br->bit_pos_ + table->bits);
  return table->value;
}

// Reads packed symbol depending on GREEN channel
#define BITS_SPECIAL_MARKER 0x100  // something large enough (and a bit-mask)
#define PACKED_NON_LITERAL_CODE 0  // must be < NUM_LITERAL_CODES
static WEBP_INLINE int ReadPackedSymbols(const HTreeGroup* group,
                                         VP8LBitReader* const br,
                                         uint32_t* const dst) {
  const uint32_t val = VP8LPrefetchBits(br) & (HUFFMAN_PACKED_TABLE_SIZE - 1);
  const HuffmanCode32 code = group->packed_table[val];
  assert(group->use_packed_table);
  if (code.bits < BITS_SPECIAL_MARKER) {
    VP8LSetBitPos(br, br->bit_pos_ + code.bits);
    *dst = code.value;
    return PACKED_NON_LITERAL_CODE;
  } else {
    VP8LSetBitPos(br, br->bit_pos_ + code.bits - BITS_SPECIAL_MARKER);
    assert(code.value >= NUM_LITERAL_CODES);
    return code.value;
  }
}

static int AccumulateHCode(HuffmanCode hcode, int shift,
                           HuffmanCode32* const huff) {
  huff->bits += hcode.bits;
  huff->value |= (uint32_t)hcode.value << shift;
  assert(huff->bits <= HUFFMAN_TABLE_BITS);
  return hcode.bits;
}

static void BuildPackedTable(HTreeGroup* const htree_group) {
  uint32_t code;
  for (code = 0; code < HUFFMAN_PACKED_TABLE_SIZE; ++code) {
    uint32_t bits = code;
    HuffmanCode32* const huff = &htree_group->packed_table[bits];
    HuffmanCode hcode = htree_group->htrees[GREEN][bits];
    if (hcode.value >= NUM_LITERAL_CODES) {
      huff->bits = hcode.bits + BITS_SPECIAL_MARKER;
      huff->value = hcode.value;
    } else {
      huff->bits = 0;
      huff->value = 0;
      bits >>= AccumulateHCode(hcode, 8, huff);
      bits >>= AccumulateHCode(htree_group->htrees[RED][bits], 16, huff);
      bits >>= AccumulateHCode(htree_group->htrees[BLUE][bits], 0, huff);
      bits >>= AccumulateHCode(htree_group->htrees[ALPHA][bits], 24, huff);
      (void)bits;
    }
  }
}

static int ReadHuffmanCodeLengths(
    VP8LDecoder* const dec, const int* const code_length_code_lengths,
    int num_symbols, int* const code_lengths) {
  int ok = 0;
  VP8LBitReader* const br = &dec->br_;
  int symbol;
  int max_symbol;
  int prev_code_len = DEFAULT_CODE_LENGTH;
  HuffmanCode table[1 << LENGTHS_TABLE_BITS];

  if (!VP8LBuildHuffmanTable(table, LENGTHS_TABLE_BITS,
                             code_length_code_lengths,
                             NUM_CODE_LENGTH_CODES)) {
    goto End;
  }

  if (VP8LReadBits(br, 1)) {    // use length
    const int length_nbits = 2 + 2 * VP8LReadBits(br, 3);
    max_symbol = 2 + VP8LReadBits(br, length_nbits);
    if (max_symbol > num_symbols) {
      goto End;
    }
  } else {
    max_symbol = num_symbols;
  }

  symbol = 0;
  while (symbol < num_symbols) {
    const HuffmanCode* p;
    int code_len;
    if (max_symbol-- == 0) break;
    VP8LFillBitWindow(br);
    p = &table[VP8LPrefetchBits(br) & LENGTHS_TABLE_MASK];
    VP8LSetBitPos(br, br->bit_pos_ + p->bits);
    code_len = p->value;
    if (code_len < kCodeLengthLiterals) {
      code_lengths[symbol++] = code_len;
      if (code_len != 0) prev_code_len = code_len;
    } else {
      const int use_prev = (code_len == kCodeLengthRepeatCode);
      const int slot = code_len - kCodeLengthLiterals;
      const int extra_bits = kCodeLengthExtraBits[slot];
      const int repeat_offset = kCodeLengthRepeatOffsets[slot];
      int repeat = VP8LReadBits(br, extra_bits) + repeat_offset;
      if (symbol + repeat > num_symbols) {
        goto End;
      } else {
        const int length = use_prev ? prev_code_len : 0;
        while (repeat-- > 0) code_lengths[symbol++] = length;
      }
    }
  }
  ok = 1;

 End:
  if (!ok) dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
  return ok;
}

// 'code_lengths' is pre-allocated temporary buffer, used for creating Huffman
// tree.
static int ReadHuffmanCode(int alphabet_size, VP8LDecoder* const dec,
                           int* const code_lengths, HuffmanCode* const table) {
  int ok = 0;
  int size = 0;
  VP8LBitReader* const br = &dec->br_;
  const int simple_code = VP8LReadBits(br, 1);

  memset(code_lengths, 0, alphabet_size * sizeof(*code_lengths));

  if (simple_code) {  // Read symbols, codes & code lengths directly.
    const int num_symbols = VP8LReadBits(br, 1) + 1;
    const int first_symbol_len_code = VP8LReadBits(br, 1);
    // The first code is either 1 bit or 8 bit code.
    int symbol = VP8LReadBits(br, (first_symbol_len_code == 0) ? 1 : 8);
    code_lengths[symbol] = 1;
    // The second code (if present), is always 8 bit long.
    if (num_symbols == 2) {
      symbol = VP8LReadBits(br, 8);
      code_lengths[symbol] = 1;
    }
    ok = 1;
  } else {  // Decode Huffman-coded code lengths.
    int i;
    int code_length_code_lengths[NUM_CODE_LENGTH_CODES] = { 0 };
    const int num_codes = VP8LReadBits(br, 4) + 4;
    if (num_codes > NUM_CODE_LENGTH_CODES) {
      dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
      return 0;
    }

    for (i = 0; i < num_codes; ++i) {
      code_length_code_lengths[kCodeLengthCodeOrder[i]] = VP8LReadBits(br, 3);
    }
    ok = ReadHuffmanCodeLengths(dec, code_length_code_lengths, alphabet_size,
                                code_lengths);
  }

  ok = ok && !br->eos_;
  if (ok) {
    size = VP8LBuildHuffmanTable(table, HUFFMAN_TABLE_BITS,
                                 code_lengths, alphabet_size);
  }
  if (!ok || size == 0) {
    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
    return 0;
  }
  return size;
}

static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
                            int color_cache_bits, int allow_recursion) {
  int i, j;
  VP8LBitReader* const br = &dec->br_;
  VP8LMetadata* const hdr = &dec->hdr_;
  uint32_t* huffman_image = NULL;
  HTreeGroup* htree_groups = NULL;
  HuffmanCode* huffman_tables = NULL;
  HuffmanCode* next = NULL;
  int num_htree_groups = 1;
  int max_alphabet_size = 0;
  int* code_lengths = NULL;
  const int table_size = kTableSize[color_cache_bits];

  if (allow_recursion && VP8LReadBits(br, 1)) {
    // use meta Huffman codes.
    const int huffman_precision = VP8LReadBits(br, 3) + 2;
    const int huffman_xsize = VP8LSubSampleSize(xsize, huffman_precision);
    const int huffman_ysize = VP8LSubSampleSize(ysize, huffman_precision);
    const int huffman_pixs = huffman_xsize * huffman_ysize;
    if (!DecodeImageStream(huffman_xsize, huffman_ysize, 0, dec,
                           &huffman_image)) {
      goto Error;
    }
    hdr->huffman_subsample_bits_ = huffman_precision;
    for (i = 0; i < huffman_pixs; ++i) {
      // The huffman data is stored in red and green bytes.
      const int group = (huffman_image[i] >> 8) & 0xffff;
      huffman_image[i] = group;
      if (group >= num_htree_groups) {
        num_htree_groups = group + 1;
      }
    }
  }

  if (br->eos_) goto Error;

  // Find maximum alphabet size for the htree group.
  for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; ++j) {
    int alphabet_size = kAlphabetSize[j];
    if (j == 0 && color_cache_bits > 0) {
      alphabet_size += 1 << color_cache_bits;
    }
    if (max_alphabet_size < alphabet_size) {
      max_alphabet_size = alphabet_size;
    }
  }

  huffman_tables = (HuffmanCode*)WebPSafeMalloc(num_htree_groups * table_size,
                                                sizeof(*huffman_tables));
  htree_groups = VP8LHtreeGroupsNew(num_htree_groups);
  code_lengths = (int*)WebPSafeCalloc((uint64_t)max_alphabet_size,
                                      sizeof(*code_lengths));

  if (htree_groups == NULL || code_lengths == NULL || huffman_tables == NULL) {
    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
    goto Error;
  }

  next = huffman_tables;
  for (i = 0; i < num_htree_groups; ++i) {
    HTreeGroup* const htree_group = &htree_groups[i];
    HuffmanCode** const htrees = htree_group->htrees;
    int size;
    int total_size = 0;
    int is_trivial_literal = 1;
    int max_bits = 0;
    for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; ++j) {
      int alphabet_size = kAlphabetSize[j];
      htrees[j] = next;
      if (j == 0 && color_cache_bits > 0) {
        alphabet_size += 1 << color_cache_bits;
      }
      size = ReadHuffmanCode(alphabet_size, dec, code_lengths, next);
      if (size == 0) {
        goto Error;
      }
      if (is_trivial_literal && kLiteralMap[j] == 1) {
        is_trivial_literal = (next->bits == 0);
      }
      total_size += next->bits;
      next += size;
      if (j <= ALPHA) {
        int local_max_bits = code_lengths[0];
        int k;
        for (k = 1; k < alphabet_size; ++k) {
          if (code_lengths[k] > local_max_bits) {
            local_max_bits = code_lengths[k];
          }
        }
        max_bits += local_max_bits;
      }
    }
    htree_group->is_trivial_literal = is_trivial_literal;
    htree_group->is_trivial_code = 0;
    if (is_trivial_literal) {
      const int red = htrees[RED][0].value;
      const int blue = htrees[BLUE][0].value;
      const int alpha = htrees[ALPHA][0].value;
      htree_group->literal_arb =
          ((uint32_t)alpha << 24) | (red << 16) | blue;
      if (total_size == 0 && htrees[GREEN][0].value < NUM_LITERAL_CODES) {
        htree_group->is_trivial_code = 1;
        htree_group->literal_arb |= htrees[GREEN][0].value << 8;
      }
    }
    htree_group->use_packed_table = !htree_group->is_trivial_code &&
                                    (max_bits < HUFFMAN_PACKED_BITS);
    if (htree_group->use_packed_table) BuildPackedTable(htree_group);
  }
  WebPSafeFree(code_lengths);

  // All OK. Finalize pointers and return.
  hdr->huffman_image_ = huffman_image;
  hdr->num_htree_groups_ = num_htree_groups;
  hdr->htree_groups_ = htree_groups;
  hdr->huffman_tables_ = huffman_tables;
  return 1;

 Error:
  WebPSafeFree(code_lengths);
  WebPSafeFree(huffman_image);
  WebPSafeFree(huffman_tables);
  VP8LHtreeGroupsFree(htree_groups);
  return 0;
}

//------------------------------------------------------------------------------
// Scaling.

#if !defined(WEBP_REDUCE_SIZE)
static int AllocateAndInitRescaler(VP8LDecoder* const dec, VP8Io* const io) {
  const int num_channels = 4;
  const int in_width = io->mb_w;
  const int out_width = io->scaled_width;
  const int in_height = io->mb_h;
  const int out_height = io->scaled_height;
  const uint64_t work_size = 2 * num_channels * (uint64_t)out_width;
  rescaler_t* work;        // Rescaler work area.
  const uint64_t scaled_data_size = (uint64_t)out_width;
  uint32_t* scaled_data;  // Temporary storage for scaled BGRA data.
  const uint64_t memory_size = sizeof(*dec->rescaler) +
                               work_size * sizeof(*work) +
                               scaled_data_size * sizeof(*scaled_data);
  uint8_t* memory = (uint8_t*)WebPSafeMalloc(memory_size, sizeof(*memory));
  if (memory == NULL) {
    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
    return 0;
  }
  assert(dec->rescaler_memory == NULL);
  dec->rescaler_memory = memory;

  dec->rescaler = (WebPRescaler*)memory;
  memory += sizeof(*dec->rescaler);
  work = (rescaler_t*)memory;
  memory += work_size * sizeof(*work);
  scaled_data = (uint32_t*)memory;

  WebPRescalerInit(dec->rescaler, in_width, in_height, (uint8_t*)scaled_data,
                   out_width, out_height, 0, num_channels, work);
  return 1;
}
#endif   // WEBP_REDUCE_SIZE

//------------------------------------------------------------------------------
// Export to ARGB

#if !defined(WEBP_REDUCE_SIZE)

// We have special "export" function since we need to convert from BGRA
static int Export(WebPRescaler* const rescaler, WEBP_CSP_MODE colorspace,
                  int rgba_stride, uint8_t* const rgba) {
  uint32_t* const src = (uint32_t*)rescaler->dst;
  const int dst_width = rescaler->dst_width;
  int num_lines_out = 0;
  while (WebPRescalerHasPendingOutput(rescaler)) {
    uint8_t* const dst = rgba + num_lines_out * rgba_stride;
    WebPRescalerExportRow(rescaler);
    WebPMultARGBRow(src, dst_width, 1);
    VP8LConvertFromBGRA(src, dst_width, colorspace, dst);
    ++num_lines_out;
  }
  return num_lines_out;
}

// Emit scaled rows.
static int EmitRescaledRowsRGBA(const VP8LDecoder* const dec,
                                uint8_t* in, int in_stride, int mb_h,
                                uint8_t* const out, int out_stride) {
  const WEBP_CSP_MODE colorspace = dec->output_->colorspace;
  int num_lines_in = 0;
  int num_lines_out = 0;
  while (num_lines_in < mb_h) {
    uint8_t* const row_in = in + num_lines_in * in_stride;
    uint8_t* const row_out = out + num_lines_out * out_stride;
    const int lines_left = mb_h - num_lines_in;
    const int needed_lines = WebPRescaleNeededLines(dec->rescaler, lines_left);
    int lines_imported;
    assert(needed_lines > 0 && needed_lines <= lines_left);
    WebPMultARGBRows(row_in, in_stride,
                     dec->rescaler->src_width, needed_lines, 0);
    lines_imported =
        WebPRescalerImport(dec->rescaler, lines_left, row_in, in_stride);
    assert(lines_imported == needed_lines);
    num_lines_in += lines_imported;
    num_lines_out += Export(dec->rescaler, colorspace, out_stride, row_out);
  }
  return num_lines_out;
}

#endif   // WEBP_REDUCE_SIZE

// Emit rows without any scaling.
static int EmitRows(WEBP_CSP_MODE colorspace,
                    const uint8_t* row_in, int in_stride,
                    int mb_w, int mb_h,
                    uint8_t* const out, int out_stride) {
  int lines = mb_h;
  uint8_t* row_out = out;
  while (lines-- > 0) {
    VP8LConvertFromBGRA((const uint32_t*)row_in, mb_w, colorspace, row_out);
    row_in += in_stride;
    row_out += out_stride;
  }
  return mb_h;  // Num rows out == num rows in.
}

//------------------------------------------------------------------------------
// Export to YUVA

static void ConvertToYUVA(const uint32_t* const src, int width, int y_pos,
                          const WebPDecBuffer* const output) {
  const WebPYUVABuffer* const buf = &output->u.YUVA;

  // first, the luma plane
  WebPConvertARGBToY(src, buf->y + y_pos * buf->y_stride, width);

  // then U/V planes
  {
    uint8_t* const u = buf->u + (y_pos >> 1) * buf->u_stride;
    uint8_t* const v = buf->v + (y_pos >> 1) * buf->v_stride;
    // even lines: store values
    // odd lines: average with previous values
    WebPConvertARGBToUV(src, u, v, width, !(y_pos & 1));
  }
  // Lastly, store alpha if needed.
  if (buf->a != NULL) {
    uint8_t* const a = buf->a + y_pos * buf->a_stride;
#if defined(WORDS_BIGENDIAN)
    WebPExtractAlpha((uint8_t*)src + 0, 0, width, 1, a, 0);
#else
    WebPExtractAlpha((uint8_t*)src + 3, 0, width, 1, a, 0);
#endif
  }
}

static int ExportYUVA(const VP8LDecoder* const dec, int y_pos) {
  WebPRescaler* const rescaler = dec->rescaler;
  uint32_t* const src = (uint32_t*)rescaler->dst;
  const int dst_width = rescaler->dst_width;
  int num_lines_out = 0;
  while (WebPRescalerHasPendingOutput(rescaler)) {
    WebPRescalerExportRow(rescaler);
    WebPMultARGBRow(src, dst_width, 1);
    ConvertToYUVA(src, dst_width, y_pos, dec->output_);
    ++y_pos;
    ++num_lines_out;
  }
  return num_lines_out;
}

static int EmitRescaledRowsYUVA(const VP8LDecoder* const dec,
                                uint8_t* in, int in_stride, int mb_h) {
  int num_lines_in = 0;
  int y_pos = dec->last_out_row_;
  while (num_lines_in < mb_h) {
    const int lines_left = mb_h - num_lines_in;
    const int needed_lines = WebPRescaleNeededLines(dec->rescaler, lines_left);
    int lines_imported;
    WebPMultARGBRows(in, in_stride, dec->rescaler->src_width, needed_lines, 0);
    lines_imported =
        WebPRescalerImport(dec->rescaler, lines_left, in, in_stride);
    assert(lines_imported == needed_lines);
    num_lines_in += lines_imported;
    in += needed_lines * in_stride;
    y_pos += ExportYUVA(dec, y_pos);
  }
  return y_pos;
}

static int EmitRowsYUVA(const VP8LDecoder* const dec,
                        const uint8_t* in, int in_stride,
                        int mb_w, int num_rows) {
  int y_pos = dec->last_out_row_;
  while (num_rows-- > 0) {
    ConvertToYUVA((const uint32_t*)in, mb_w, y_pos, dec->output_);
    in += in_stride;
    ++y_pos;
  }
  return y_pos;
}

//------------------------------------------------------------------------------
// Cropping.

// Sets io->mb_y, io->mb_h & io->mb_w according to start row, end row and
// crop options. Also updates the input data pointer, so that it points to the
// start of the cropped window. Note that pixels are in ARGB format even if
// 'in_data' is uint8_t*.
// Returns true if the crop window is not empty.
static int SetCropWindow(VP8Io* const io, int y_start, int y_end,
                         uint8_t** const in_data, int pixel_stride) {
  assert(y_start < y_end);
  assert(io->crop_left < io->crop_right);
  if (y_end > io->crop_bottom) {
    y_end = io->crop_bottom;  // make sure we don't overflow on last row.
  }
  if (y_start < io->crop_top) {
    const int delta = io->crop_top - y_start;
    y_start = io->crop_top;
    *in_data += delta * pixel_stride;
  }
  if (y_start >= y_end) return 0;  // Crop window is empty.

  *in_data += io->crop_left * sizeof(uint32_t);

  io->mb_y = y_start - io->crop_top;
  io->mb_w = io->crop_right - io->crop_left;
  io->mb_h = y_end - y_start;
  return 1;  // Non-empty crop window.
}

//------------------------------------------------------------------------------

static WEBP_INLINE int GetMetaIndex(
    const uint32_t* const image, int xsize, int bits, int x, int y) {
  if (bits == 0) return 0;
  return image[xsize * (y >> bits) + (x >> bits)];
}

static WEBP_INLINE HTreeGroup* GetHtreeGroupForPos(VP8LMetadata* const hdr,
                                                   int x, int y) {
  const int meta_index = GetMetaIndex(hdr->huffman_image_, hdr->huffman_xsize_,
                                      hdr->huffman_subsample_bits_, x, y);
  assert(meta_index < hdr->num_htree_groups_);
  return hdr->htree_groups_ + meta_index;
}

//------------------------------------------------------------------------------
// Main loop, with custom row-processing function

typedef void (*ProcessRowsFunc)(VP8LDecoder* const dec, int row);

static void ApplyInverseTransforms(VP8LDecoder* const dec, int num_rows,
                                   const uint32_t* const rows) {
  int n = dec->next_transform_;
  const int cache_pixs = dec->width_ * num_rows;
  const int start_row = dec->last_row_;
  const int end_row = start_row + num_rows;
  const uint32_t* rows_in = rows;
  uint32_t* const rows_out = dec->argb_cache_;

  // Inverse transforms.
  while (n-- > 0) {
    VP8LTransform* const transform = &dec->transforms_[n];
    VP8LInverseTransform(transform, start_row, end_row, rows_in, rows_out);
    rows_in = rows_out;
  }
  if (rows_in != rows_out) {
    // No transform called, hence just copy.
    memcpy(rows_out, rows_in, cache_pixs * sizeof(*rows_out));
  }
}

// Processes (transforms, scales & color-converts) the rows decoded after the
// last call.
static void ProcessRows(VP8LDecoder* const dec, int row) {
  const uint32_t* const rows = dec->pixels_ + dec->width_ * dec->last_row_;
  const int num_rows = row - dec->last_row_;

  assert(row <= dec->io_->crop_bottom);
  // We can't process more than NUM_ARGB_CACHE_ROWS at a time (that's the size
  // of argb_cache_), but we currently don't need more than that.
  assert(num_rows <= NUM_ARGB_CACHE_ROWS);
  if (num_rows > 0) {    // Emit output.
    VP8Io* const io = dec->io_;
    uint8_t* rows_data = (uint8_t*)dec->argb_cache_;
    const int in_stride = io->width * sizeof(uint32_t);  // in unit of RGBA

    ApplyInverseTransforms(dec, num_rows, rows);
    if (!SetCropWindow(io, dec->last_row_, row, &rows_data, in_stride)) {
      // Nothing to output (this time).
    } else {
      const WebPDecBuffer* const output = dec->output_;
      if (WebPIsRGBMode(output->colorspace)) {  // convert to RGBA
        const WebPRGBABuffer* const buf = &output->u.RGBA;
        uint8_t* const rgba = buf->rgba + dec->last_out_row_ * buf->stride;
        const int num_rows_out =
#if !defined(WEBP_REDUCE_SIZE)
         io->use_scaling ?
            EmitRescaledRowsRGBA(dec, rows_data, in_stride, io->mb_h,
                                 rgba, buf->stride) :
#endif  // WEBP_REDUCE_SIZE
            EmitRows(output->colorspace, rows_data, in_stride,
                     io->mb_w, io->mb_h, rgba, buf->stride);
        // Update 'last_out_row_'.
        dec->last_out_row_ += num_rows_out;
      } else {                              // convert to YUVA
        dec->last_out_row_ = io->use_scaling ?
            EmitRescaledRowsYUVA(dec, rows_data, in_stride, io->mb_h) :
            EmitRowsYUVA(dec, rows_data, in_stride, io->mb_w, io->mb_h);
      }
      assert(dec->last_out_row_ <= output->height);
    }
  }

  // Update 'last_row_'.
  dec->last_row_ = row;
  assert(dec->last_row_ <= dec->height_);
}

// Row-processing for the special case when alpha data contains only one
// transform (color indexing), and trivial non-green literals.
static int Is8bOptimizable(const VP8LMetadata* const hdr) {
  int i;
  if (hdr->color_cache_size_ > 0) return 0;
  // When the Huffman tree contains only one symbol, we can skip the
  // call to ReadSymbol() for red/blue/alpha channels.
  for (i = 0; i < hdr->num_htree_groups_; ++i) {
    HuffmanCode** const htrees = hdr->htree_groups_[i].htrees;
    if (htrees[RED][0].bits > 0) return 0;
    if (htrees[BLUE][0].bits > 0) return 0;
    if (htrees[ALPHA][0].bits > 0) return 0;
  }
  return 1;
}

static void AlphaApplyFilter(ALPHDecoder* const alph_dec,
                             int first_row, int last_row,
                             uint8_t* out, int stride) {
  if (alph_dec->filter_ != WEBP_FILTER_NONE) {
    int y;
    const uint8_t* prev_line = alph_dec->prev_line_;
    assert(WebPUnfilters[alph_dec->filter_] != NULL);
    for (y = first_row; y < last_row; ++y) {
      WebPUnfilters[alph_dec->filter_](prev_line, out, out, stride);
      prev_line = out;
      out += stride;
    }
    alph_dec->prev_line_ = prev_line;
  }
}

static void ExtractPalettedAlphaRows(VP8LDecoder* const dec, int last_row) {
  // For vertical and gradient filtering, we need to decode the part above the
  // crop_top row, in order to have the correct spatial predictors.
  ALPHDecoder* const alph_dec = (ALPHDecoder*)dec->io_->opaque;
  const int top_row =
      (alph_dec->filter_ == WEBP_FILTER_NONE ||
       alph_dec->filter_ == WEBP_FILTER_HORIZONTAL) ? dec->io_->crop_top
                                                    : dec->last_row_;
  const int first_row = (dec->last_row_ < top_row) ? top_row : dec->last_row_;
  assert(last_row <= dec->io_->crop_bottom);
  if (last_row > first_row) {
    // Special method for paletted alpha data. We only process the cropped area.
    const int width = dec->io_->width;
    uint8_t* out = alph_dec->output_ + width * first_row;
    const uint8_t* const in =
      (uint8_t*)dec->pixels_ + dec->width_ * first_row;
    VP8LTransform* const transform = &dec->transforms_[0];
    assert(dec->next_transform_ == 1);
    assert(transform->type_ == COLOR_INDEXING_TRANSFORM);
    VP8LColorIndexInverseTransformAlpha(transform, first_row, last_row,
                                        in, out);
    AlphaApplyFilter(alph_dec, first_row, last_row, out, width);
  }
  dec->last_row_ = dec->last_out_row_ = last_row;
}

//------------------------------------------------------------------------------
// Helper functions for fast pattern copy (8b and 32b)

// cyclic rotation of pattern word
static WEBP_INLINE uint32_t Rotate8b(uint32_t V) {
#if defined(WORDS_BIGENDIAN)
  return ((V & 0xff000000u) >> 24) | (V << 8);
#else
  return ((V & 0xffu) << 24) | (V >> 8);
#endif
}

// copy 1, 2 or 4-bytes pattern
static WEBP_INLINE void CopySmallPattern8b(const uint8_t* src, uint8_t* dst,
                                           int length, uint32_t pattern) {
  int i;
  // align 'dst' to 4-bytes boundary. Adjust the pattern along the way.
  while ((uintptr_t)dst & 3) {
    *dst++ = *src++;
    pattern = Rotate8b(pattern);
    --length;
  }
  // Copy the pattern 4 bytes at a time.
  for (i = 0; i < (length >> 2); ++i) {
    ((uint32_t*)dst)[i] = pattern;
  }
  // Finish with left-overs. 'pattern' is still correctly positioned,
  // so no Rotate8b() call is needed.
  for (i <<= 2; i < length; ++i) {
    dst[i] = src[i];
  }
}

static WEBP_INLINE void CopyBlock8b(uint8_t* const dst, int dist, int length) {
  const uint8_t* src = dst - dist;
  if (length >= 8) {
    uint32_t pattern = 0;
    switch (dist) {
      case 1:
        pattern = src[0];
#if defined(__arm__) || defined(_M_ARM)   // arm doesn't like multiply that much
        pattern |= pattern << 8;
        pattern |= pattern << 16;
#elif defined(WEBP_USE_MIPS_DSP_R2)
        __asm__ volatile ("replv.qb %0, %0" : "+r"(pattern));
#else
        pattern = 0x01010101u * pattern;
#endif
        break;
      case 2:
        memcpy(&pattern, src, sizeof(uint16_t));
#if defined(__arm__) || defined(_M_ARM)
        pattern |= pattern << 16;
#elif defined(WEBP_USE_MIPS_DSP_R2)
        __asm__ volatile ("replv.ph %0, %0" : "+r"(pattern));
#else
        pattern = 0x00010001u * pattern;
#endif
        break;
      case 4:
        memcpy(&pattern, src, sizeof(uint32_t));
        break;
      default:
        goto Copy;
        break;
    }
    CopySmallPattern8b(src, dst, length, pattern);
    return;
  }
 Copy:
  if (dist >= length) {  // no overlap -> use memcpy()
    memcpy(dst, src, length * sizeof(*dst));
  } else {
    int i;
    for (i = 0; i < length; ++i) dst[i] = src[i];
  }
}

// copy pattern of 1 or 2 uint32_t's
static WEBP_INLINE void CopySmallPattern32b(const uint32_t* src,
                                            uint32_t* dst,
                                            int length, uint64_t pattern) {
  int i;
  if ((uintptr_t)dst & 4) {           // Align 'dst' to 8-bytes boundary.
    *dst++ = *src++;
    pattern = (pattern >> 32) | (pattern << 32);
    --length;
  }
  assert(0 == ((uintptr_t)dst & 7));
  for (i = 0; i < (length >> 1); ++i) {
    ((uint64_t*)dst)[i] = pattern;    // Copy the pattern 8 bytes at a time.
  }
  if (length & 1) {                   // Finish with left-over.
    dst[i << 1] = src[i << 1];
  }
}

static WEBP_INLINE void CopyBlock32b(uint32_t* const dst,
                                     int dist, int length) {
  const uint32_t* const src = dst - dist;
  if (dist <= 2 && length >= 4 && ((uintptr_t)dst & 3) == 0) {
    uint64_t pattern;
    if (dist == 1) {
      pattern = (uint64_t)src[0];
      pattern |= pattern << 32;
    } else {
      memcpy(&pattern, src, sizeof(pattern));
    }
    CopySmallPattern32b(src, dst, length, pattern);
  } else if (dist >= length) {  // no overlap
    memcpy(dst, src, length * sizeof(*dst));
  } else {
    int i;
    for (i = 0; i < length; ++i) dst[i] = src[i];
  }
}

//------------------------------------------------------------------------------

static int DecodeAlphaData(VP8LDecoder* const dec, uint8_t* const data,
                           int width, int height, int last_row) {
  int ok = 1;
  int row = dec->last_pixel_ / width;
  int col = dec->last_pixel_ % width;
  VP8LBitReader* const br = &dec->br_;
  VP8LMetadata* const hdr = &dec->hdr_;
  int pos = dec->last_pixel_;         // current position
  const int end = width * height;     // End of data
  const int last = width * last_row;  // Last pixel to decode
  const int len_code_limit = NUM_LITERAL_CODES + NUM_LENGTH_CODES;
  const int mask = hdr->huffman_mask_;
  const HTreeGroup* htree_group =
      (pos < last) ? GetHtreeGroupForPos(hdr, col, row) : NULL;
  assert(pos <= end);
  assert(last_row <= height);
  assert(Is8bOptimizable(hdr));

  while (!br->eos_ && pos < last) {
    int code;
    // Only update when changing tile.
    if ((col & mask) == 0) {
      htree_group = GetHtreeGroupForPos(hdr, col, row);
    }
    assert(htree_group != NULL);
    VP8LFillBitWindow(br);
    code = ReadSymbol(htree_group->htrees[GREEN], br);
    if (code < NUM_LITERAL_CODES) {  // Literal
      data[pos] = code;
      ++pos;
      ++col;
      if (col >= width) {
        col = 0;
        ++row;
        if (row <= last_row && (row % NUM_ARGB_CACHE_ROWS == 0)) {
          ExtractPalettedAlphaRows(dec, row);
        }
      }
    } else if (code < len_code_limit) {  // Backward reference
      int dist_code, dist;
      const int length_sym = code - NUM_LITERAL_CODES;
      const int length = GetCopyLength(length_sym, br);
      const int dist_symbol = ReadSymbol(htree_group->htrees[DIST], br);
      VP8LFillBitWindow(br);
      dist_code = GetCopyDistance(dist_symbol, br);
      dist = PlaneCodeToDistance(width, dist_code);
      if (pos >= dist && end - pos >= length) {
        CopyBlock8b(data + pos, dist, length);
      } else {
        ok = 0;
        goto End;
      }
      pos += length;
      col += length;
      while (col >= width) {
        col -= width;
        ++row;
        if (row <= last_row && (row % NUM_ARGB_CACHE_ROWS == 0)) {
          ExtractPalettedAlphaRows(dec, row);
        }
      }
      if (pos < last && (col & mask)) {
        htree_group = GetHtreeGroupForPos(hdr, col, row);
      }
    } else {  // Not reached
      ok = 0;
      goto End;
    }
    br->eos_ = VP8LIsEndOfStream(br);
  }
  // Process the remaining rows corresponding to last row-block.
  ExtractPalettedAlphaRows(dec, row > last_row ? last_row : row);

 End:
  br->eos_ = VP8LIsEndOfStream(br);
  if (!ok || (br->eos_ && pos < end)) {
    ok = 0;
    dec->status_ = br->eos_ ? VP8_STATUS_SUSPENDED
                            : VP8_STATUS_BITSTREAM_ERROR;
  } else {
    dec->last_pixel_ = pos;
  }
  return ok;
}

static void SaveState(VP8LDecoder* const dec, int last_pixel) {
  assert(dec->incremental_);
  dec->saved_br_ = dec->br_;
  dec->saved_last_pixel_ = last_pixel;
  if (dec->hdr_.color_cache_size_ > 0) {
    VP8LColorCacheCopy(&dec->hdr_.color_cache_, &dec->hdr_.saved_color_cache_);
  }
}

static void RestoreState(VP8LDecoder* const dec) {
  assert(dec->br_.eos_);
  dec->status_ = VP8_STATUS_SUSPENDED;
  dec->br_ = dec->saved_br_;
  dec->last_pixel_ = dec->saved_last_pixel_;
  if (dec->hdr_.color_cache_size_ > 0) {
    VP8LColorCacheCopy(&dec->hdr_.saved_color_cache_, &dec->hdr_.color_cache_);
  }
}

#define SYNC_EVERY_N_ROWS 8  // minimum number of rows between check-points
static int DecodeImageData(VP8LDecoder* const dec, uint32_t* const data,
                           int width, int height, int last_row,
                           ProcessRowsFunc process_func) {
  int row = dec->last_pixel_ / width;
  int col = dec->last_pixel_ % width;
  VP8LBitReader* const br = &dec->br_;
  VP8LMetadata* const hdr = &dec->hdr_;
  uint32_t* src = data + dec->last_pixel_;
  uint32_t* last_cached = src;
  uint32_t* const src_end = data + width * height;     // End of data
  uint32_t* const src_last = data + width * last_row;  // Last pixel to decode
  const int len_code_limit = NUM_LITERAL_CODES + NUM_LENGTH_CODES;
  const int color_cache_limit = len_code_limit + hdr->color_cache_size_;
  int next_sync_row = dec->incremental_ ? row : 1 << 24;
  VP8LColorCache* const color_cache =
      (hdr->color_cache_size_ > 0) ? &hdr->color_cache_ : NULL;
  const int mask = hdr->huffman_mask_;
  const HTreeGroup* htree_group =
      (src < src_last) ? GetHtreeGroupForPos(hdr, col, row) : NULL;
  assert(dec->last_row_ < last_row);
  assert(src_last <= src_end);

  while (src < src_last) {
    int code;
    if (row >= next_sync_row) {
      SaveState(dec, (int)(src - data));
      next_sync_row = row + SYNC_EVERY_N_ROWS;
    }
    // Only update when changing tile. Note we could use this test:
    // if "((((prev_col ^ col) | prev_row ^ row)) > mask)" -> tile changed
    // but that's actually slower and needs storing the previous col/row.
    if ((col & mask) == 0) {
      htree_group = GetHtreeGroupForPos(hdr, col, row);
    }
    assert(htree_group != NULL);
    if (htree_group->is_trivial_code) {
      *src = htree_group->literal_arb;
      goto AdvanceByOne;
    }
    VP8LFillBitWindow(br);
    if (htree_group->use_packed_table) {
      code = ReadPackedSymbols(htree_group, br, src);
      if (VP8LIsEndOfStream(br)) break;
      if (code == PACKED_NON_LITERAL_CODE) goto AdvanceByOne;
    } else {
      code = ReadSymbol(htree_group->htrees[GREEN], br);
    }
    if (VP8LIsEndOfStream(br)) break;
    if (code < NUM_LITERAL_CODES) {  // Literal
      if (htree_group->is_trivial_literal) {
        *src = htree_group->literal_arb | (code << 8);
      } else {
        int red, blue, alpha;
        red = ReadSymbol(htree_group->htrees[RED], br);
        VP8LFillBitWindow(br);
        blue = ReadSymbol(htree_group->htrees[BLUE], br);
        alpha = ReadSymbol(htree_group->htrees[ALPHA], br);
        if (VP8LIsEndOfStream(br)) break;
        *src = ((uint32_t)alpha << 24) | (red << 16) | (code << 8) | blue;
      }
    AdvanceByOne:
      ++src;
      ++col;
      if (col >= width) {
        col = 0;
        ++row;
        if (process_func != NULL) {
          if (row <= last_row && (row % NUM_ARGB_CACHE_ROWS == 0)) {
            process_func(dec, row);
          }
        }
        if (color_cache != NULL) {
          while (last_cached < src) {
            VP8LColorCacheInsert(color_cache, *last_cached++);
          }
        }
      }
    } else if (code < len_code_limit) {  // Backward reference
      int dist_code, dist;
      const int length_sym = code - NUM_LITERAL_CODES;
      const int length = GetCopyLength(length_sym, br);
      const int dist_symbol = ReadSymbol(htree_group->htrees[DIST], br);
      VP8LFillBitWindow(br);
      dist_code = GetCopyDistance(dist_symbol, br);
      dist = PlaneCodeToDistance(width, dist_code);
      if (VP8LIsEndOfStream(br)) break;
      if (src - data < (ptrdiff_t)dist || src_end - src < (ptrdiff_t)length) {
        goto Error;
      } else {
        CopyBlock32b(src, dist, length);
      }
      src += length;
      col += length;
      while (col >= width) {
        col -= width;
        ++row;
        if (process_func != NULL) {
          if (row <= last_row && (row % NUM_ARGB_CACHE_ROWS == 0)) {
            process_func(dec, row);
          }
        }
      }
      // Because of the check done above (before 'src' was incremented by
      // 'length'), the following holds true.
      assert(src <= src_end);
      if (col & mask) htree_group = GetHtreeGroupForPos(hdr, col, row);
      if (color_cache != NULL) {
        while (last_cached < src) {
          VP8LColorCacheInsert(color_cache, *last_cached++);
        }
      }
    } else if (code < color_cache_limit) {  // Color cache
      const int key = code - len_code_limit;
      assert(color_cache != NULL);
      while (last_cached < src) {
        VP8LColorCacheInsert(color_cache, *last_cached++);
      }
      *src = VP8LColorCacheLookup(color_cache, key);
      goto AdvanceByOne;
    } else {  // Not reached
      goto Error;
    }
  }

  br->eos_ = VP8LIsEndOfStream(br);
  if (dec->incremental_ && br->eos_ && src < src_end) {
    RestoreState(dec);
  } else if (!br->eos_) {
    // Process the remaining rows corresponding to last row-block.
    if (process_func != NULL) {
      process_func(dec, row > last_row ? last_row : row);
    }
    dec->status_ = VP8_STATUS_OK;
    dec->last_pixel_ = (int)(src - data);  // end-of-scan marker
  } else {
    // if not incremental, and we are past the end of buffer (eos_=1), then this
    // is a real bitstream error.
    goto Error;
  }
  return 1;

 Error:
  dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
  return 0;
}

// -----------------------------------------------------------------------------
// VP8LTransform

static void ClearTransform(VP8LTransform* const transform) {
  WebPSafeFree(transform->data_);
  transform->data_ = NULL;
}

// For security reason, we need to remap the color map to span
// the total possible bundled values, and not just the num_colors.
static int ExpandColorMap(int num_colors, VP8LTransform* const transform) {
  int i;
  const int final_num_colors = 1 << (8 >> transform->bits_);
  uint32_t* const new_color_map =
      (uint32_t*)WebPSafeMalloc((uint64_t)final_num_colors,
                                sizeof(*new_color_map));
  if (new_color_map == NULL) {
    return 0;
  } else {
    uint8_t* const data = (uint8_t*)transform->data_;
    uint8_t* const new_data = (uint8_t*)new_color_map;
    new_color_map[0] = transform->data_[0];
    for (i = 4; i < 4 * num_colors; ++i) {
      // Equivalent to AddPixelEq(), on a byte-basis.
      new_data[i] = (data[i] + new_data[i - 4]) & 0xff;
    }
    for (; i < 4 * final_num_colors; ++i) {
      new_data[i] = 0;  // black tail.
    }
    WebPSafeFree(transform->data_);
    transform->data_ = new_color_map;
  }
  return 1;
}

static int ReadTransform(int* const xsize, int const* ysize,
                         VP8LDecoder* const dec) {
  int ok = 1;
  VP8LBitReader* const br = &dec->br_;
  VP8LTransform* transform = &dec->transforms_[dec->next_transform_];
  const VP8LImageTransformType type =
      (VP8LImageTransformType)VP8LReadBits(br, 2);

  // Each transform type can only be present once in the stream.
  if (dec->transforms_seen_ & (1U << type)) {
    return 0;  // Already there, let's not accept the second same transform.
  }
  dec->transforms_seen_ |= (1U << type);

  transform->type_ = type;
  transform->xsize_ = *xsize;
  transform->ysize_ = *ysize;
  transform->data_ = NULL;
  ++dec->next_transform_;
  assert(dec->next_transform_ <= NUM_TRANSFORMS);

  switch (type) {
    case PREDICTOR_TRANSFORM:
    case CROSS_COLOR_TRANSFORM:
      transform->bits_ = VP8LReadBits(br, 3) + 2;
      ok = DecodeImageStream(VP8LSubSampleSize(transform->xsize_,
                                               transform->bits_),
                             VP8LSubSampleSize(transform->ysize_,
                                               transform->bits_),
                             0, dec, &transform->data_);
      break;
    case COLOR_INDEXING_TRANSFORM: {
       const int num_colors = VP8LReadBits(br, 8) + 1;
       const int bits = (num_colors > 16) ? 0
                      : (num_colors > 4) ? 1
                      : (num_colors > 2) ? 2
                      : 3;
       *xsize = VP8LSubSampleSize(transform->xsize_, bits);
       transform->bits_ = bits;
       ok = DecodeImageStream(num_colors, 1, 0, dec, &transform->data_);
       ok = ok && ExpandColorMap(num_colors, transform);
      break;
    }
    case SUBTRACT_GREEN:
      break;
    default:
      assert(0);    // can't happen
      break;
  }

  return ok;
}

// -----------------------------------------------------------------------------
// VP8LMetadata

static void InitMetadata(VP8LMetadata* const hdr) {
  assert(hdr != NULL);
  memset(hdr, 0, sizeof(*hdr));
}

static void ClearMetadata(VP8LMetadata* const hdr) {
  assert(hdr != NULL);

  WebPSafeFree(hdr->huffman_image_);
  WebPSafeFree(hdr->huffman_tables_);
  VP8LHtreeGroupsFree(hdr->htree_groups_);
  VP8LColorCacheClear(&hdr->color_cache_);
  VP8LColorCacheClear(&hdr->saved_color_cache_);
  InitMetadata(hdr);
}

// -----------------------------------------------------------------------------
// VP8LDecoder

VP8LDecoder* VP8LNew(void) {
  VP8LDecoder* const dec = (VP8LDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
  if (dec == NULL) return NULL;
  dec->status_ = VP8_STATUS_OK;
  dec->state_ = READ_DIM;

  VP8LDspInit();  // Init critical function pointers.

  return dec;
}

void VP8LClear(VP8LDecoder* const dec) {
  int i;
  if (dec == NULL) return;
  ClearMetadata(&dec->hdr_);

  WebPSafeFree(dec->pixels_);
  dec->pixels_ = NULL;
  for (i = 0; i < dec->next_transform_; ++i) {
    ClearTransform(&dec->transforms_[i]);
  }
  dec->next_transform_ = 0;
  dec->transforms_seen_ = 0;

  WebPSafeFree(dec->rescaler_memory);
  dec->rescaler_memory = NULL;

  dec->output_ = NULL;   // leave no trace behind
}

void VP8LDelete(VP8LDecoder* const dec) {
  if (dec != NULL) {
    VP8LClear(dec);
    WebPSafeFree(dec);
  }
}

static void UpdateDecoder(VP8LDecoder* const dec, int width, int height) {
  VP8LMetadata* const hdr = &dec->hdr_;
  const int num_bits = hdr->huffman_subsample_bits_;
  dec->width_ = width;
  dec->height_ = height;

  hdr->huffman_xsize_ = VP8LSubSampleSize(width, num_bits);
  hdr->huffman_mask_ = (num_bits == 0) ? ~0 : (1 << num_bits) - 1;
}

static int DecodeImageStream(int xsize, int ysize,
                             int is_level0,
                             VP8LDecoder* const dec,
                             uint32_t** const decoded_data) {
  int ok = 1;
  int transform_xsize = xsize;
  int transform_ysize = ysize;
  VP8LBitReader* const br = &dec->br_;
  VP8LMetadata* const hdr = &dec->hdr_;
  uint32_t* data = NULL;
  int color_cache_bits = 0;

  // Read the transforms (may recurse).
  if (is_level0) {
    while (ok && VP8LReadBits(br, 1)) {
      ok = ReadTransform(&transform_xsize, &transform_ysize, dec);
    }
  }

  // Color cache
  if (ok && VP8LReadBits(br, 1)) {
    color_cache_bits = VP8LReadBits(br, 4);
    ok = (color_cache_bits >= 1 && color_cache_bits <= MAX_CACHE_BITS);
    if (!ok) {
      dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
      goto End;
    }
  }

  // Read the Huffman codes (may recurse).
  ok = ok && ReadHuffmanCodes(dec, transform_xsize, transform_ysize,
                              color_cache_bits, is_level0);
  if (!ok) {
    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
    goto End;
  }

  // Finish setting up the color-cache
  if (color_cache_bits > 0) {
    hdr->color_cache_size_ = 1 << color_cache_bits;
    if (!VP8LColorCacheInit(&hdr->color_cache_, color_cache_bits)) {
      dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
      ok = 0;
      goto End;
    }
  } else {
    hdr->color_cache_size_ = 0;
  }
  UpdateDecoder(dec, transform_xsize, transform_ysize);

  if (is_level0) {   // level 0 complete
    dec->state_ = READ_HDR;
    goto End;
  }

  {
    const uint64_t total_size = (uint64_t)transform_xsize * transform_ysize;
    data = (uint32_t*)WebPSafeMalloc(total_size, sizeof(*data));
    if (data == NULL) {
      dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
      ok = 0;
      goto End;
    }
  }

  // Use the Huffman trees to decode the LZ77 encoded data.
  ok = DecodeImageData(dec, data, transform_xsize, transform_ysize,
                       transform_ysize, NULL);
  ok = ok && !br->eos_;

 End:
  if (!ok) {
    WebPSafeFree(data);
    ClearMetadata(hdr);
  } else {
    if (decoded_data != NULL) {
      *decoded_data = data;
    } else {
      // We allocate image data in this function only for transforms. At level 0
      // (that is: not the transforms), we shouldn't have allocated anything.
      assert(data == NULL);
      assert(is_level0);
    }
    dec->last_pixel_ = 0;  // Reset for future DECODE_DATA_FUNC() calls.
    if (!is_level0) ClearMetadata(hdr);  // Clean up temporary data behind.
  }
  return ok;
}

//------------------------------------------------------------------------------
// Allocate internal buffers dec->pixels_ and dec->argb_cache_.
static int AllocateInternalBuffers32b(VP8LDecoder* const dec, int final_width) {
  const uint64_t num_pixels = (uint64_t)dec->width_ * dec->height_;
  // Scratch buffer corresponding to top-prediction row for transforming the
  // first row in the row-blocks. Not needed for paletted alpha.
  const uint64_t cache_top_pixels = (uint16_t)final_width;
  // Scratch buffer for temporary BGRA storage. Not needed for paletted alpha.
  const uint64_t cache_pixels = (uint64_t)final_width * NUM_ARGB_CACHE_ROWS;
  const uint64_t total_num_pixels =
      num_pixels + cache_top_pixels + cache_pixels;

  assert(dec->width_ <= final_width);
  dec->pixels_ = (uint32_t*)WebPSafeMalloc(total_num_pixels, sizeof(uint32_t));
  if (dec->pixels_ == NULL) {
    dec->argb_cache_ = NULL;    // for sanity check
    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
    return 0;
  }
  dec->argb_cache_ = dec->pixels_ + num_pixels + cache_top_pixels;
  return 1;
}

static int AllocateInternalBuffers8b(VP8LDecoder* const dec) {
  const uint64_t total_num_pixels = (uint64_t)dec->width_ * dec->height_;
  dec->argb_cache_ = NULL;    // for sanity check
  dec->pixels_ = (uint32_t*)WebPSafeMalloc(total_num_pixels, sizeof(uint8_t));
  if (dec->pixels_ == NULL) {
    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
    return 0;
  }
  return 1;
}

//------------------------------------------------------------------------------

// Special row-processing that only stores the alpha data.
static void ExtractAlphaRows(VP8LDecoder* const dec, int last_row) {
  int cur_row = dec->last_row_;
  int num_rows = last_row - cur_row;
  const uint32_t* in = dec->pixels_ + dec->width_ * cur_row;

  assert(last_row <= dec->io_->crop_bottom);
  while (num_rows > 0) {
    const int num_rows_to_process =
        (num_rows > NUM_ARGB_CACHE_ROWS) ? NUM_ARGB_CACHE_ROWS : num_rows;
    // Extract alpha (which is stored in the green plane).
    ALPHDecoder* const alph_dec = (ALPHDecoder*)dec->io_->opaque;
    uint8_t* const output = alph_dec->output_;
    const int width = dec->io_->width;      // the final width (!= dec->width_)
    const int cache_pixs = width * num_rows_to_process;
    uint8_t* const dst = output + width * cur_row;
    const uint32_t* const src = dec->argb_cache_;
    ApplyInverseTransforms(dec, num_rows_to_process, in);
    WebPExtractGreen(src, dst, cache_pixs);
    AlphaApplyFilter(alph_dec,
                     cur_row, cur_row + num_rows_to_process, dst, width);
    num_rows -= num_rows_to_process;
    in += num_rows_to_process * dec->width_;
    cur_row += num_rows_to_process;
  }
  assert(cur_row == last_row);
  dec->last_row_ = dec->last_out_row_ = last_row;
}

int VP8LDecodeAlphaHeader(ALPHDecoder* const alph_dec,
                          const uint8_t* const data, size_t data_size) {
  int ok = 0;
  VP8LDecoder* dec = VP8LNew();

  if (dec == NULL) return 0;

  assert(alph_dec != NULL);
  alph_dec->vp8l_dec_ = dec;

  dec->width_ = alph_dec->width_;
  dec->height_ = alph_dec->height_;
  dec->io_ = &alph_dec->io_;
  dec->io_->opaque = alph_dec;
  dec->io_->width = alph_dec->width_;
  dec->io_->height = alph_dec->height_;

  dec->status_ = VP8_STATUS_OK;
  VP8LInitBitReader(&dec->br_, data, data_size);

  if (!DecodeImageStream(alph_dec->width_, alph_dec->height_, 1, dec, NULL)) {
    goto Err;
  }

  // Special case: if alpha data uses only the color indexing transform and
  // doesn't use color cache (a frequent case), we will use DecodeAlphaData()
  // method that only needs allocation of 1 byte per pixel (alpha channel).
  if (dec->next_transform_ == 1 &&
      dec->transforms_[0].type_ == COLOR_INDEXING_TRANSFORM &&
      Is8bOptimizable(&dec->hdr_)) {
    alph_dec->use_8b_decode_ = 1;
    ok = AllocateInternalBuffers8b(dec);
  } else {
    // Allocate internal buffers (note that dec->width_ may have changed here).
    alph_dec->use_8b_decode_ = 0;
    ok = AllocateInternalBuffers32b(dec, alph_dec->width_);
  }

  if (!ok) goto Err;

  return 1;

 Err:
  VP8LDelete(alph_dec->vp8l_dec_);
  alph_dec->vp8l_dec_ = NULL;
  return 0;
}

int VP8LDecodeAlphaImageStream(ALPHDecoder* const alph_dec, int last_row) {
  VP8LDecoder* const dec = alph_dec->vp8l_dec_;
  assert(dec != NULL);
  assert(last_row <= dec->height_);

  if (dec->last_row_ >= last_row) {
    return 1;  // done
  }

  if (!alph_dec->use_8b_decode_) WebPInitAlphaProcessing();

  // Decode (with special row processing).
  return alph_dec->use_8b_decode_ ?
      DecodeAlphaData(dec, (uint8_t*)dec->pixels_, dec->width_, dec->height_,
                      last_row) :
      DecodeImageData(dec, dec->pixels_, dec->width_, dec->height_,
                      last_row, ExtractAlphaRows);
}

//------------------------------------------------------------------------------

int VP8LDecodeHeader(VP8LDecoder* const dec, VP8Io* const io) {
  int width, height, has_alpha;

  if (dec == NULL) return 0;
  if (io == NULL) {
    dec->status_ = VP8_STATUS_INVALID_PARAM;
    return 0;
  }

  dec->io_ = io;
  dec->status_ = VP8_STATUS_OK;
  VP8LInitBitReader(&dec->br_, io->data, io->data_size);
  if (!ReadImageInfo(&dec->br_, &width, &height, &has_alpha)) {
    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
    goto Error;
  }
  dec->state_ = READ_DIM;
  io->width = width;
  io->height = height;

  if (!DecodeImageStream(width, height, 1, dec, NULL)) goto Error;
  return 1;

 Error:
  VP8LClear(dec);
  assert(dec->status_ != VP8_STATUS_OK);
  return 0;
}

int VP8LDecodeImage(VP8LDecoder* const dec) {
  VP8Io* io = NULL;
  WebPDecParams* params = NULL;

  // Sanity checks.
  if (dec == NULL) return 0;

  assert(dec->hdr_.huffman_tables_ != NULL);
  assert(dec->hdr_.htree_groups_ != NULL);
  assert(dec->hdr_.num_htree_groups_ > 0);

  io = dec->io_;
  assert(io != NULL);
  params = (WebPDecParams*)io->opaque;
  assert(params != NULL);

  // Initialization.
  if (dec->state_ != READ_DATA) {
    dec->output_ = params->output;
    assert(dec->output_ != NULL);

    if (!WebPIoInitFromOptions(params->options, io, MODE_BGRA)) {
      dec->status_ = VP8_STATUS_INVALID_PARAM;
      goto Err;
    }

    if (!AllocateInternalBuffers32b(dec, io->width)) goto Err;

#if !defined(WEBP_REDUCE_SIZE)
    if (io->use_scaling && !AllocateAndInitRescaler(dec, io)) goto Err;
#else
    if (io->use_scaling) {
      dec->status_ = VP8_STATUS_INVALID_PARAM;
      goto Err;
    }
#endif
    if (io->use_scaling || WebPIsPremultipliedMode(dec->output_->colorspace)) {
      // need the alpha-multiply functions for premultiplied output or rescaling
      WebPInitAlphaProcessing();
    }

    if (!WebPIsRGBMode(dec->output_->colorspace)) {
      WebPInitConvertARGBToYUV();
      if (dec->output_->u.YUVA.a != NULL) WebPInitAlphaProcessing();
    }
    if (dec->incremental_) {
      if (dec->hdr_.color_cache_size_ > 0 &&
          dec->hdr_.saved_color_cache_.colors_ == NULL) {
        if (!VP8LColorCacheInit(&dec->hdr_.saved_color_cache_,
                                dec->hdr_.color_cache_.hash_bits_)) {
          dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
          goto Err;
        }
      }
    }
    dec->state_ = READ_DATA;
  }

  // Decode.
  if (!DecodeImageData(dec, dec->pixels_, dec->width_, dec->height_,
                       io->crop_bottom, ProcessRows)) {
    goto Err;
  }

  params->last_y = dec->last_out_row_;
  return 1;

 Err:
  VP8LClear(dec);
  assert(dec->status_ != VP8_STATUS_OK);
  return 0;
}

//------------------------------------------------------------------------------