aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/icu/i18n/translit.cpp
blob: c7d6b510576d247ce3911533c03c9d6084a80186 (plain) (blame)
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
// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
 **********************************************************************
 *   Copyright (C) 1999-2016, International Business Machines
 *   Corporation and others.  All Rights Reserved.
 **********************************************************************
 *   Date        Name        Description
 *   11/17/99    aliu        Creation.
 **********************************************************************
 */

#include "utypeinfo.h"  // for 'typeid' to work

#include "unicode/utypes.h"

#if !UCONFIG_NO_TRANSLITERATION

#include "unicode/putil.h"
#include "unicode/translit.h"
#include "unicode/locid.h"
#include "unicode/msgfmt.h"
#include "unicode/rep.h"
#include "unicode/resbund.h"
#include "unicode/unifilt.h"
#include "unicode/uniset.h"
#include "unicode/uscript.h"
#include "unicode/strenum.h"
#include "unicode/utf16.h"
#include "cpdtrans.h"
#include "nultrans.h"
#include "rbt_data.h"
#include "rbt_pars.h"
#include "rbt.h"
#include "transreg.h"
#include "name2uni.h"
#include "nortrans.h"
#include "remtrans.h"
#include "titletrn.h"
#include "tolowtrn.h"
#include "toupptrn.h"
#include "uni2name.h"
#include "brktrans.h"
#include "esctrn.h"
#include "unesctrn.h"
#include "tridpars.h"
#include "anytrans.h"
#include "util.h"
#include "hash.h"
#include "mutex.h"
#include "ucln_in.h"
#include "uassert.h"
#include "cmemory.h"
#include "cstring.h"
#include "uinvchar.h"

static const UChar TARGET_SEP  = 0x002D; /*-*/
static const UChar ID_DELIM    = 0x003B; /*;*/
static const UChar VARIANT_SEP = 0x002F; // '/'

/**
 * Prefix for resource bundle key for the display name for a
 * transliterator.  The ID is appended to this to form the key.
 * The resource bundle value should be a String.
 */
static const char RB_DISPLAY_NAME_PREFIX[] = "%Translit%%";

/**
 * Prefix for resource bundle key for the display name for a
 * transliterator SCRIPT.  The ID is appended to this to form the key.
 * The resource bundle value should be a String.
 */
static const char RB_SCRIPT_DISPLAY_NAME_PREFIX[] = "%Translit%";

/**
 * Resource bundle key for display name pattern.
 * The resource bundle value should be a String forming a
 * MessageFormat pattern, e.g.:
 * "{0,choice,0#|1#{1} Transliterator|2#{1} to {2} Transliterator}".
 */
static const char RB_DISPLAY_NAME_PATTERN[] = "TransliteratorNamePattern";

/**
 * Resource bundle key for the list of RuleBasedTransliterator IDs.
 * The resource bundle value should be a String[] with each element
 * being a valid ID.  The ID will be appended to RB_RULE_BASED_PREFIX
 * to obtain the class name in which the RB_RULE key will be sought.
 */
static const char RB_RULE_BASED_IDS[] = "RuleBasedTransliteratorIDs";

/**
 * The mutex controlling access to registry object.
 */
static icu::UMutex registryMutex;

/**
 * System transliterator registry; non-null when initialized.
 */
static icu::TransliteratorRegistry* registry = 0;

// Macro to check/initialize the registry. ONLY USE WITHIN
// MUTEX. Avoids function call when registry is initialized.
#define HAVE_REGISTRY(status) (registry!=0 || initializeRegistry(status))

U_NAMESPACE_BEGIN

UOBJECT_DEFINE_ABSTRACT_RTTI_IMPLEMENTATION(Transliterator)

/**
 * Return TRUE if the given UTransPosition is valid for text of
 * the given length.
 */
static inline UBool positionIsValid(UTransPosition& index, int32_t len) {
    return !(index.contextStart < 0 ||
             index.start < index.contextStart ||
             index.limit < index.start ||
             index.contextLimit < index.limit ||
             len < index.contextLimit);
}

/**
 * Default constructor.
 * @param theID the string identifier for this transliterator
 * @param theFilter the filter.  Any character for which
 * <tt>filter.contains()</tt> returns <tt>FALSE</tt> will not be
 * altered by this transliterator.  If <tt>filter</tt> is
 * <tt>null</tt> then no filtering is applied.
 */
Transliterator::Transliterator(const UnicodeString& theID,
                               UnicodeFilter* adoptedFilter) :
    UObject(), ID(theID), filter(adoptedFilter),
    maximumContextLength(0)
{
    // NUL-terminate the ID string, which is a non-aliased copy.
    ID.append((UChar)0);
    ID.truncate(ID.length()-1);
}

/**
 * Destructor.
 */
Transliterator::~Transliterator() {
    if (filter) {
        delete filter;
    }
}

/**
 * Copy constructor.
 */
Transliterator::Transliterator(const Transliterator& other) :
    UObject(other), ID(other.ID), filter(0),
    maximumContextLength(other.maximumContextLength)
{
    // NUL-terminate the ID string, which is a non-aliased copy.
    ID.append((UChar)0);
    ID.truncate(ID.length()-1);

    if (other.filter != 0) {
        // We own the filter, so we must have our own copy
        filter = other.filter->clone();
    }
}

Transliterator* Transliterator::clone() const {
    return NULL;
}

/**
 * Assignment operator.
 */
Transliterator& Transliterator::operator=(const Transliterator& other) {
    if (this == &other) { return *this; }  // self-assignment: no-op
    ID = other.ID;
    // NUL-terminate the ID string
    ID.getTerminatedBuffer();

    maximumContextLength = other.maximumContextLength;
    adoptFilter((other.filter == 0) ? 0 : other.filter->clone());
    return *this;
}

/**
 * Transliterates a segment of a string.  <code>Transliterator</code> API.
 * @param text the string to be transliterated
 * @param start the beginning index, inclusive; <code>0 <= start
 * <= limit</code>.
 * @param limit the ending index, exclusive; <code>start <= limit
 * <= text.length()</code>.
 * @return the new limit index, or -1
 */
int32_t Transliterator::transliterate(Replaceable& text,
                                      int32_t start, int32_t limit) const {
    if (start < 0 ||
        limit < start ||
        text.length() < limit) {
        return -1;
    }

    UTransPosition offsets;
    offsets.contextStart= start;
    offsets.contextLimit = limit;
    offsets.start = start;
    offsets.limit = limit;
    filteredTransliterate(text, offsets, FALSE, TRUE);
    return offsets.limit;
}

/**
 * Transliterates an entire string in place. Convenience method.
 * @param text the string to be transliterated
 */
void Transliterator::transliterate(Replaceable& text) const {
    transliterate(text, 0, text.length());
}

/**
 * Transliterates the portion of the text buffer that can be
 * transliterated unambiguosly after new text has been inserted,
 * typically as a result of a keyboard event.  The new text in
 * <code>insertion</code> will be inserted into <code>text</code>
 * at <code>index.contextLimit</code>, advancing
 * <code>index.contextLimit</code> by <code>insertion.length()</code>.
 * Then the transliterator will try to transliterate characters of
 * <code>text</code> between <code>index.start</code> and
 * <code>index.contextLimit</code>.  Characters before
 * <code>index.start</code> will not be changed.
 *
 * <p>Upon return, values in <code>index</code> will be updated.
 * <code>index.contextStart</code> will be advanced to the first
 * character that future calls to this method will read.
 * <code>index.start</code> and <code>index.contextLimit</code> will
 * be adjusted to delimit the range of text that future calls to
 * this method may change.
 *
 * <p>Typical usage of this method begins with an initial call
 * with <code>index.contextStart</code> and <code>index.contextLimit</code>
 * set to indicate the portion of <code>text</code> to be
 * transliterated, and <code>index.start == index.contextStart</code>.
 * Thereafter, <code>index</code> can be used without
 * modification in future calls, provided that all changes to
 * <code>text</code> are made via this method.
 *
 * <p>This method assumes that future calls may be made that will
 * insert new text into the buffer.  As a result, it only performs
 * unambiguous transliterations.  After the last call to this
 * method, there may be untransliterated text that is waiting for
 * more input to resolve an ambiguity.  In order to perform these
 * pending transliterations, clients should call {@link
 * #finishKeyboardTransliteration} after the last call to this
 * method has been made.
 * 
 * @param text the buffer holding transliterated and untransliterated text
 * @param index an array of three integers.
 *
 * <ul><li><code>index.contextStart</code>: the beginning index,
 * inclusive; <code>0 <= index.contextStart <= index.contextLimit</code>.
 *
 * <li><code>index.contextLimit</code>: the ending index, exclusive;
 * <code>index.contextStart <= index.contextLimit <= text.length()</code>.
 * <code>insertion</code> is inserted at
 * <code>index.contextLimit</code>.
 *
 * <li><code>index.start</code>: the next character to be
 * considered for transliteration; <code>index.contextStart <=
 * index.start <= index.contextLimit</code>.  Characters before
 * <code>index.start</code> will not be changed by future calls
 * to this method.</ul>
 *
 * @param insertion text to be inserted and possibly
 * transliterated into the translation buffer at
 * <code>index.contextLimit</code>.  If <code>null</code> then no text
 * is inserted.
 * @see #START
 * @see #LIMIT
 * @see #CURSOR
 * @see #handleTransliterate
 * @exception IllegalArgumentException if <code>index</code>
 * is invalid
 */
void Transliterator::transliterate(Replaceable& text,
                                   UTransPosition& index,
                                   const UnicodeString& insertion,
                                   UErrorCode &status) const {
    _transliterate(text, index, &insertion, status);
}

/**
 * Transliterates the portion of the text buffer that can be
 * transliterated unambiguosly after a new character has been
 * inserted, typically as a result of a keyboard event.  This is a
 * convenience method; see {@link
 * #transliterate(Replaceable, int[], String)} for details.
 * @param text the buffer holding transliterated and
 * untransliterated text
 * @param index an array of three integers.  See {@link
 * #transliterate(Replaceable, int[], String)}.
 * @param insertion text to be inserted and possibly
 * transliterated into the translation buffer at
 * <code>index.contextLimit</code>.
 * @see #transliterate(Replaceable, int[], String)
 */
void Transliterator::transliterate(Replaceable& text,
                                   UTransPosition& index,
                                   UChar32 insertion,
                                   UErrorCode& status) const {
    UnicodeString str(insertion);
    _transliterate(text, index, &str, status);
}

/**
 * Transliterates the portion of the text buffer that can be
 * transliterated unambiguosly.  This is a convenience method; see
 * {@link #transliterate(Replaceable, int[], String)} for
 * details.
 * @param text the buffer holding transliterated and
 * untransliterated text
 * @param index an array of three integers.  See {@link
 * #transliterate(Replaceable, int[], String)}.
 * @see #transliterate(Replaceable, int[], String)
 */
void Transliterator::transliterate(Replaceable& text,
                                   UTransPosition& index,
                                   UErrorCode& status) const {
    _transliterate(text, index, 0, status);
}

/**
 * Finishes any pending transliterations that were waiting for
 * more characters.  Clients should call this method as the last
 * call after a sequence of one or more calls to
 * <code>transliterate()</code>.
 * @param text the buffer holding transliterated and
 * untransliterated text.
 * @param index the array of indices previously passed to {@link
 * #transliterate}
 */
void Transliterator::finishTransliteration(Replaceable& text,
                                           UTransPosition& index) const {
    if (!positionIsValid(index, text.length())) {
        return;
    }

    filteredTransliterate(text, index, FALSE, TRUE);
}

/**
 * This internal method does keyboard transliteration.  If the
 * 'insertion' is non-null then we append it to 'text' before
 * proceeding.  This method calls through to the pure virtual
 * framework method handleTransliterate() to do the actual
 * work.
 */
void Transliterator::_transliterate(Replaceable& text,
                                    UTransPosition& index,
                                    const UnicodeString* insertion,
                                    UErrorCode &status) const {
    if (U_FAILURE(status)) {
        return;
    }

    if (!positionIsValid(index, text.length())) {
        status = U_ILLEGAL_ARGUMENT_ERROR;
        return;
    }

//    int32_t originalStart = index.contextStart;
    if (insertion != 0) {
        text.handleReplaceBetween(index.limit, index.limit, *insertion);
        index.limit += insertion->length();
        index.contextLimit += insertion->length();
    }

    if (index.limit > 0 &&
        U16_IS_LEAD(text.charAt(index.limit - 1))) {
        // Oops, there is a dangling lead surrogate in the buffer.
        // This will break most transliterators, since they will
        // assume it is part of a pair.  Don't transliterate until
        // more text comes in.
        return;
    }

    filteredTransliterate(text, index, TRUE, TRUE);

#if 0
    // TODO
    // I CAN'T DO what I'm attempting below now that the Kleene star
    // operator is supported.  For example, in the rule

    //   ([:Lu:]+) { x } > $1;

    // what is the maximum context length?  getMaximumContextLength()
    // will return 1, but this is just the length of the ante context
    // part of the pattern string -- 1 character, which is a standin
    // for a Quantifier, which contains a StringMatcher, which
    // contains a UnicodeSet.

    // There is a complicated way to make this work again, and that's
    // to add a "maximum left context" protocol into the
    // UnicodeMatcher hierarchy.  At present I'm not convinced this is
    // worth it.

    // ---

    // The purpose of the code below is to keep the context small
    // while doing incremental transliteration.  When part of the left
    // context (between contextStart and start) is no longer needed,
    // we try to advance contextStart past that portion.  We use the
    // maximum context length to do so.
    int32_t newCS = index.start;
    int32_t n = getMaximumContextLength();
    while (newCS > originalStart && n-- > 0) {
        --newCS;
        newCS -= U16_LENGTH(text.char32At(newCS)) - 1;
    }
    index.contextStart = uprv_max(newCS, originalStart);
#endif
}

/**
 * This method breaks up the input text into runs of unfiltered
 * characters.  It passes each such run to
 * <subclass>.handleTransliterate().  Subclasses that can handle the
 * filter logic more efficiently themselves may override this method.
 *
 * All transliteration calls in this class go through this method.
 */
void Transliterator::filteredTransliterate(Replaceable& text,
                                           UTransPosition& index,
                                           UBool incremental,
                                           UBool rollback) const {
    // Short circuit path for transliterators with no filter in
    // non-incremental mode.
    if (filter == 0 && !rollback) {
        handleTransliterate(text, index, incremental);
        return;
    }

    //----------------------------------------------------------------------
    // This method processes text in two groupings:
    //
    // RUNS -- A run is a contiguous group of characters which are contained
    // in the filter for this transliterator (filter.contains(ch) == TRUE).
    // Text outside of runs may appear as context but it is not modified.
    // The start and limit Position values are narrowed to each run.
    //
    // PASSES (incremental only) -- To make incremental mode work correctly,
    // each run is broken up into n passes, where n is the length (in code
    // points) of the run.  Each pass contains the first n characters.  If a
    // pass is completely transliterated, it is committed, and further passes
    // include characters after the committed text.  If a pass is blocked,
    // and does not transliterate completely, then this method rolls back
    // the changes made during the pass, extends the pass by one code point,
    // and tries again.
    //----------------------------------------------------------------------
    
    // globalLimit is the limit value for the entire operation.  We
    // set index.limit to the end of each unfiltered run before
    // calling handleTransliterate(), so we need to maintain the real
    // value of index.limit here.  After each transliteration, we
    // update globalLimit for insertions or deletions that have
    // happened.
    int32_t globalLimit = index.limit;
    
    // If there is a non-null filter, then break the input text up.  Say the
    // input text has the form:
    //   xxxabcxxdefxx
    // where 'x' represents a filtered character (filter.contains('x') ==
    // false).  Then we break this up into:
    //   xxxabc xxdef xx
    // Each pass through the loop consumes a run of filtered
    // characters (which are ignored) and a subsequent run of
    // unfiltered characters (which are transliterated).
    
    for (;;) {

        if (filter != NULL) {
            // Narrow the range to be transliterated to the first segment
            // of unfiltered characters at or after index.start.

            // Advance past filtered chars
            UChar32 c;
            while (index.start < globalLimit &&
                   !filter->contains(c=text.char32At(index.start))) {
                index.start += U16_LENGTH(c);
            }

            // Find the end of this run of unfiltered chars
            index.limit = index.start;
            while (index.limit < globalLimit &&
                   filter->contains(c=text.char32At(index.limit))) {
                index.limit += U16_LENGTH(c);
            }
        }

        // Check to see if the unfiltered run is empty.  This only
        // happens at the end of the string when all the remaining
        // characters are filtered.
        if (index.limit == index.start) {
            // assert(index.start == globalLimit);
            break;
        }

        // Is this run incremental?  If there is additional
        // filtered text (if limit < globalLimit) then we pass in
        // an incremental value of FALSE to force the subclass to
        // complete the transliteration for this run.
        UBool isIncrementalRun =
            (index.limit < globalLimit ? FALSE : incremental);
        
        int32_t delta;

        // Implement rollback.  To understand the need for rollback,
        // consider the following transliterator:
        //
        //  "t" is "a > A;"
        //  "u" is "A > b;"
        //  "v" is a compound of "t; NFD; u" with a filter [:Ll:]
        //
        // Now apply "c" to the input text "a".  The result is "b".  But if
        // the transliteration is done incrementally, then the NFD holds
        // things up after "t" has already transformed "a" to "A".  When
        // finishTransliterate() is called, "A" is _not_ processed because
        // it gets excluded by the [:Ll:] filter, and the end result is "A"
        // -- incorrect.  The problem is that the filter is applied to a
        // partially-transliterated result, when we only want it to apply to
        // input text.  Although this example hinges on a compound
        // transliterator containing NFD and a specific filter, it can
        // actually happen with any transliterator which may do a partial
        // transformation in incremental mode into characters outside its
        // filter.
        //
        // To handle this, when in incremental mode we supply characters to
        // handleTransliterate() in several passes.  Each pass adds one more
        // input character to the input text.  That is, for input "ABCD", we
        // first try "A", then "AB", then "ABC", and finally "ABCD".  If at
        // any point we block (upon return, start < limit) then we roll
        // back.  If at any point we complete the run (upon return start ==
        // limit) then we commit that run.

        if (rollback && isIncrementalRun) {

            int32_t runStart = index.start;
            int32_t runLimit = index.limit;
            int32_t runLength =  runLimit - runStart;

            // Make a rollback copy at the end of the string
            int32_t rollbackOrigin = text.length();
            text.copy(runStart, runLimit, rollbackOrigin);

            // Variables reflecting the commitment of completely
            // transliterated text.  passStart is the runStart, advanced
            // past committed text.  rollbackStart is the rollbackOrigin,
            // advanced past rollback text that corresponds to committed
            // text.
            int32_t passStart = runStart;
            int32_t rollbackStart = rollbackOrigin;

            // The limit for each pass; we advance by one code point with
            // each iteration.
            int32_t passLimit = index.start;

            // Total length, in 16-bit code units, of uncommitted text.
            // This is the length to be rolled back.
            int32_t uncommittedLength = 0;

            // Total delta (change in length) for all passes
            int32_t totalDelta = 0;

            // PASS MAIN LOOP -- Start with a single character, and extend
            // the text by one character at a time.  Roll back partial
            // transliterations and commit complete transliterations.
            for (;;) {
                // Length of additional code point, either one or two
                int32_t charLength = U16_LENGTH(text.char32At(passLimit));
                passLimit += charLength;
                if (passLimit > runLimit) {
                    break;
                }
                uncommittedLength += charLength;

                index.limit = passLimit;

                // Delegate to subclass for actual transliteration.  Upon
                // return, start will be updated to point after the
                // transliterated text, and limit and contextLimit will be
                // adjusted for length changes.
                handleTransliterate(text, index, TRUE);

                delta = index.limit - passLimit; // change in length

                // We failed to completely transliterate this pass.
                // Roll back the text.  Indices remain unchanged; reset
                // them where necessary.
                if (index.start != index.limit) {
                    // Find the rollbackStart, adjusted for length changes
                    // and the deletion of partially transliterated text.
                    int32_t rs = rollbackStart + delta - (index.limit - passStart);

                    // Delete the partially transliterated text
                    text.handleReplaceBetween(passStart, index.limit, UnicodeString());

                    // Copy the rollback text back
                    text.copy(rs, rs + uncommittedLength, passStart);

                    // Restore indices to their original values
                    index.start = passStart;
                    index.limit = passLimit;
                    index.contextLimit -= delta;
                }

                // We did completely transliterate this pass.  Update the
                // commit indices to record how far we got.  Adjust indices
                // for length change.
                else {
                    // Move the pass indices past the committed text.
                    passStart = passLimit = index.start;

                    // Adjust the rollbackStart for length changes and move
                    // it past the committed text.  All characters we've
                    // processed to this point are committed now, so zero
                    // out the uncommittedLength.
                    rollbackStart += delta + uncommittedLength;
                    uncommittedLength = 0;

                    // Adjust indices for length changes.
                    runLimit += delta;
                    totalDelta += delta;
                }
            }

            // Adjust overall limit and rollbackOrigin for insertions and
            // deletions.  Don't need to worry about contextLimit because
            // handleTransliterate() maintains that.
            rollbackOrigin += totalDelta;
            globalLimit += totalDelta;

            // Delete the rollback copy
            text.handleReplaceBetween(rollbackOrigin, rollbackOrigin + runLength, UnicodeString());

            // Move start past committed text
            index.start = passStart;
        }

        else {
            // Delegate to subclass for actual transliteration.
            int32_t limit = index.limit;
            handleTransliterate(text, index, isIncrementalRun);
            delta = index.limit - limit; // change in length

            // In a properly written transliterator, start == limit after
            // handleTransliterate() returns when incremental is false.
            // Catch cases where the subclass doesn't do this, and throw
            // an exception.  (Just pinning start to limit is a bad idea,
            // because what's probably happening is that the subclass
            // isn't transliterating all the way to the end, and it should
            // in non-incremental mode.)
            if (!incremental && index.start != index.limit) {
                // We can't throw an exception, so just fudge things
                index.start = index.limit;
            }

            // Adjust overall limit for insertions/deletions.  Don't need
            // to worry about contextLimit because handleTransliterate()
            // maintains that.
            globalLimit += delta;
        }

        if (filter == NULL || isIncrementalRun) {
            break;
        }

        // If we did completely transliterate this
        // run, then repeat with the next unfiltered run.
    }

    // Start is valid where it is.  Limit needs to be put back where
    // it was, modulo adjustments for deletions/insertions.
    index.limit = globalLimit;
}

void Transliterator::filteredTransliterate(Replaceable& text,
                                           UTransPosition& index,
                                           UBool incremental) const {
    filteredTransliterate(text, index, incremental, FALSE);
}

/**
 * Method for subclasses to use to set the maximum context length.
 * @see #getMaximumContextLength
 */
void Transliterator::setMaximumContextLength(int32_t maxContextLength) {
    maximumContextLength = maxContextLength;
}

/**
 * Returns a programmatic identifier for this transliterator.
 * If this identifier is passed to <code>getInstance()</code>, it
 * will return this object, if it has been registered.
 * @see #registerInstance
 * @see #getAvailableIDs
 */
const UnicodeString& Transliterator::getID(void) const {
    return ID;
}

/**
 * Returns a name for this transliterator that is appropriate for
 * display to the user in the default locale.  See {@link
 * #getDisplayName(Locale)} for details.
 */
UnicodeString& U_EXPORT2 Transliterator::getDisplayName(const UnicodeString& ID,
                                              UnicodeString& result) {
    return getDisplayName(ID, Locale::getDefault(), result);
}

/**
 * Returns a name for this transliterator that is appropriate for
 * display to the user in the given locale.  This name is taken
 * from the locale resource data in the standard manner of the
 * <code>java.text</code> package.
 *
 * <p>If no localized names exist in the system resource bundles,
 * a name is synthesized using a localized
 * <code>MessageFormat</code> pattern from the resource data.  The
 * arguments to this pattern are an integer followed by one or two
 * strings.  The integer is the number of strings, either 1 or 2.
 * The strings are formed by splitting the ID for this
 * transliterator at the first TARGET_SEP.  If there is no TARGET_SEP, then the
 * entire ID forms the only string.
 * @param inLocale the Locale in which the display name should be
 * localized.
 * @see java.text.MessageFormat
 */
UnicodeString& U_EXPORT2 Transliterator::getDisplayName(const UnicodeString& id,
                                              const Locale& inLocale,
                                              UnicodeString& result) {
    UErrorCode status = U_ZERO_ERROR;

    ResourceBundle bundle(U_ICUDATA_TRANSLIT, inLocale, status);

    // Suspend checking status until later...

    result.truncate(0);

    // Normalize the ID
    UnicodeString source, target, variant;
    UBool sawSource;
    TransliteratorIDParser::IDtoSTV(id, source, target, variant, sawSource);
    if (target.length() < 1) {
        // No target; malformed id
        return result;
    }
    if (variant.length() > 0) { // Change "Foo" to "/Foo"
        variant.insert(0, VARIANT_SEP);
    }
    UnicodeString ID(source);
    ID.append(TARGET_SEP).append(target).append(variant);

    // build the char* key
    if (uprv_isInvariantUString(ID.getBuffer(), ID.length())) {
        char key[200];
        uprv_strcpy(key, RB_DISPLAY_NAME_PREFIX);
        int32_t length=(int32_t)uprv_strlen(RB_DISPLAY_NAME_PREFIX);
        ID.extract(0, (int32_t)(sizeof(key)-length), key+length, (int32_t)(sizeof(key)-length), US_INV);

        // Try to retrieve a UnicodeString from the bundle.
        UnicodeString resString = bundle.getStringEx(key, status);

        if (U_SUCCESS(status) && resString.length() != 0) {
            return result = resString; // [sic] assign & return
        }

#if !UCONFIG_NO_FORMATTING
        // We have failed to get a name from the locale data.  This is
        // typical, since most transliterators will not have localized
        // name data.  The next step is to retrieve the MessageFormat
        // pattern from the locale data and to use it to synthesize the
        // name from the ID.

        status = U_ZERO_ERROR;
        resString = bundle.getStringEx(RB_DISPLAY_NAME_PATTERN, status);

        if (U_SUCCESS(status) && resString.length() != 0) {
            MessageFormat msg(resString, inLocale, status);
            // Suspend checking status until later...

            // We pass either 2 or 3 Formattable objects to msg.
            Formattable args[3];
            int32_t nargs;
            args[0].setLong(2); // # of args to follow
            args[1].setString(source);
            args[2].setString(target);
            nargs = 3;

            // Use display names for the scripts, if they exist
            UnicodeString s;
            length=(int32_t)uprv_strlen(RB_SCRIPT_DISPLAY_NAME_PREFIX);
            for (int j=1; j<=2; ++j) {
                status = U_ZERO_ERROR;
                uprv_strcpy(key, RB_SCRIPT_DISPLAY_NAME_PREFIX);
                args[j].getString(s);
                if (uprv_isInvariantUString(s.getBuffer(), s.length())) {
                    s.extract(0, sizeof(key)-length-1, key+length, (int32_t)sizeof(key)-length-1, US_INV);

                    resString = bundle.getStringEx(key, status);

                    if (U_SUCCESS(status)) {
                        args[j] = resString;
                    }
                }
            }

            status = U_ZERO_ERROR;
            FieldPosition pos; // ignored by msg
            msg.format(args, nargs, result, pos, status);
            if (U_SUCCESS(status)) {
                result.append(variant);
                return result;
            }
        }
#endif
    }

    // We should not reach this point unless there is something
    // wrong with the build or the RB_DISPLAY_NAME_PATTERN has
    // been deleted from the root RB_LOCALE_ELEMENTS resource.
    result = ID;
    return result;
}

/**
 * Returns the filter used by this transliterator, or <tt>null</tt>
 * if this transliterator uses no filter.  Caller musn't delete
 * the result!
 */
const UnicodeFilter* Transliterator::getFilter(void) const {
    return filter;
}

/**
 * Returns the filter used by this transliterator, or
 * <tt>NULL</tt> if this transliterator uses no filter.  The
 * caller must eventually delete the result.  After this call,
 * this transliterator's filter is set to <tt>NULL</tt>.
 */
UnicodeFilter* Transliterator::orphanFilter(void) {
    UnicodeFilter *result = filter;
    filter = NULL;
    return result;
}

/**
 * Changes the filter used by this transliterator.  If the filter
 * is set to <tt>null</tt> then no filtering will occur.
 *
 * <p>Callers must take care if a transliterator is in use by
 * multiple threads.  The filter should not be changed by one
 * thread while another thread may be transliterating.
 */
void Transliterator::adoptFilter(UnicodeFilter* filterToAdopt) {
    delete filter;
    filter = filterToAdopt;
}

/**
 * Returns this transliterator's inverse.  See the class
 * documentation for details.  This implementation simply inverts
 * the two entities in the ID and attempts to retrieve the
 * resulting transliterator.  That is, if <code>getID()</code>
 * returns "A-B", then this method will return the result of
 * <code>getInstance("B-A")</code>, or <code>null</code> if that
 * call fails.
 *
 * <p>This method does not take filtering into account.  The
 * returned transliterator will have no filter.
 *
 * <p>Subclasses with knowledge of their inverse may wish to
 * override this method.
 *
 * @return a transliterator that is an inverse, not necessarily
 * exact, of this transliterator, or <code>null</code> if no such
 * transliterator is registered.
 * @see #registerInstance
 */
Transliterator* Transliterator::createInverse(UErrorCode& status) const {
    UParseError parseError;
    return Transliterator::createInstance(ID, UTRANS_REVERSE,parseError,status);
}

Transliterator* U_EXPORT2
Transliterator::createInstance(const UnicodeString& ID,
                                UTransDirection dir,
                                UErrorCode& status)
{
    UParseError parseError;
    return createInstance(ID, dir, parseError, status);
}

/**
 * Returns a <code>Transliterator</code> object given its ID.
 * The ID must be either a system transliterator ID or a ID registered
 * using <code>registerInstance()</code>.
 *
 * @param ID a valid ID, as enumerated by <code>getAvailableIDs()</code>
 * @return A <code>Transliterator</code> object with the given ID
 * @see #registerInstance
 * @see #getAvailableIDs
 * @see #getID
 */
Transliterator* U_EXPORT2
Transliterator::createInstance(const UnicodeString& ID,
                                UTransDirection dir,
                                UParseError& parseError,
                                UErrorCode& status)
{
    if (U_FAILURE(status)) {
        return 0;
    }

    UnicodeString canonID;
    UVector list(status);
    if (U_FAILURE(status)) {
        return NULL;
    }

    UnicodeSet* globalFilter = nullptr;
    // TODO add code for parseError...currently unused, but
    // later may be used by parsing code...
    if (!TransliteratorIDParser::parseCompoundID(ID, dir, canonID, list, globalFilter)) {
        status = U_INVALID_ID;
        delete globalFilter;
        return NULL;
    }
    LocalPointer<UnicodeSet> lpGlobalFilter(globalFilter);
    
    TransliteratorIDParser::instantiateList(list, status);
    if (U_FAILURE(status)) {
        return NULL;
    }
    
    U_ASSERT(list.size() > 0);
    Transliterator* t = NULL;
    
    if (list.size() > 1 || canonID.indexOf(ID_DELIM) >= 0) {
        // [NOTE: If it's a compoundID, we instantiate a CompoundTransliterator even if it only
        // has one child transliterator.  This is so that toRules() will return the right thing
        // (without any inactive ID), but our main ID still comes out correct.  That is, if we
        // instantiate "(Lower);Latin-Greek;", we want the rules to come out as "::Latin-Greek;"
        // even though the ID is "(Lower);Latin-Greek;".
        t = new CompoundTransliterator(list, parseError, status);
    }
    else {
        t = (Transliterator*)list.elementAt(0);
    }
    // Check null pointer
    if (t != NULL) {
        t->setID(canonID);
        if (lpGlobalFilter.isValid()) {
            t->adoptFilter(lpGlobalFilter.orphan());
        }
    }
    else if (U_SUCCESS(status)) {
        status = U_MEMORY_ALLOCATION_ERROR;
    }
    return t;
}

/**
 * Create a transliterator from a basic ID.  This is an ID
 * containing only the forward direction source, target, and
 * variant.
 * @param id a basic ID of the form S-T or S-T/V.
 * @return a newly created Transliterator or null if the ID is
 * invalid.
 */
Transliterator* Transliterator::createBasicInstance(const UnicodeString& id,
                                                    const UnicodeString* canon) {
    UParseError pe;
    UErrorCode ec = U_ZERO_ERROR;
    TransliteratorAlias* alias = 0;
    Transliterator* t = 0;

    umtx_lock(&registryMutex);
    if (HAVE_REGISTRY(ec)) {
        t = registry->get(id, alias, ec);
    }
    umtx_unlock(&registryMutex);

    if (U_FAILURE(ec)) {
        delete t;
        delete alias;
        return 0;
    }

    // We may have not gotten a transliterator:  Because we can't
    // instantiate a transliterator from inside TransliteratorRegistry::
    // get() (that would deadlock), we sometimes pass back an alias.  This
    // contains the data we need to finish the instantiation outside the
    // registry mutex.  The alias may, in turn, generate another alias, so
    // we handle aliases in a loop.  The max times through the loop is two.
    // [alan]
    while (alias != 0) {
        U_ASSERT(t==0);
        // Rule-based aliases are handled with TransliteratorAlias::
        // parse(), followed by TransliteratorRegistry::reget().
        // Other aliases are handled with TransliteratorAlias::create().
        if (alias->isRuleBased()) {
            // Step 1. parse
            TransliteratorParser parser(ec);
            alias->parse(parser, pe, ec);
            delete alias;
            alias = 0;

            // Step 2. reget
            umtx_lock(&registryMutex);
            if (HAVE_REGISTRY(ec)) {
                t = registry->reget(id, parser, alias, ec);
            }
            umtx_unlock(&registryMutex);

            // Step 3. Loop back around!
        } else {
            t = alias->create(pe, ec);
            delete alias;
            alias = 0;
            break;
        }
        if (U_FAILURE(ec)) {
            delete t;
            delete alias;
            t = NULL;
            break;
        }
    }

    if (t != NULL && canon != NULL) {
        t->setID(*canon);
    }

    return t;
}

/**
 * Returns a <code>Transliterator</code> object constructed from
 * the given rule string.  This will be a RuleBasedTransliterator,
 * if the rule string contains only rules, or a
 * CompoundTransliterator, if it contains ID blocks, or a
 * NullTransliterator, if it contains ID blocks which parse as
 * empty for the given direction.
 */
Transliterator* U_EXPORT2
Transliterator::createFromRules(const UnicodeString& ID,
                                const UnicodeString& rules,
                                UTransDirection dir,
                                UParseError& parseError,
                                UErrorCode& status)
{
    Transliterator* t = NULL;

    TransliteratorParser parser(status);
    parser.parse(rules, dir, parseError, status);

    if (U_FAILURE(status)) {
        return 0;
    }

    // NOTE: The logic here matches that in TransliteratorRegistry.
    if (parser.idBlockVector.size() == 0 && parser.dataVector.size() == 0) {
        t = new NullTransliterator();
    }
    else if (parser.idBlockVector.size() == 0 && parser.dataVector.size() == 1) {
        t = new RuleBasedTransliterator(ID, (TransliterationRuleData*)parser.dataVector.orphanElementAt(0), TRUE);
    }
    else if (parser.idBlockVector.size() == 1 && parser.dataVector.size() == 0) {
        // idBlock, no data -- this is an alias.  The ID has
        // been munged from reverse into forward mode, if
        // necessary, so instantiate the ID in the forward
        // direction.
        if (parser.compoundFilter != NULL) {
            UnicodeString filterPattern;
            parser.compoundFilter->toPattern(filterPattern, FALSE);
            t = createInstance(filterPattern + UnicodeString(ID_DELIM)
                    + *((UnicodeString*)parser.idBlockVector.elementAt(0)), UTRANS_FORWARD, parseError, status);
        }
        else
            t = createInstance(*((UnicodeString*)parser.idBlockVector.elementAt(0)), UTRANS_FORWARD, parseError, status);


        if (t != NULL) {
            t->setID(ID);
        }
    }
    else {
        UVector transliterators(status);
        // TODO ICU-21701 missing U_FAILURE check here.
        //      Error and nullptr checking through this whole block looks suspect.
        int32_t passNumber = 1;

        int32_t limit = parser.idBlockVector.size();
        if (parser.dataVector.size() > limit)
            limit = parser.dataVector.size();

        for (int32_t i = 0; i < limit; i++) {
            if (i < parser.idBlockVector.size()) {
                UnicodeString* idBlock = (UnicodeString*)parser.idBlockVector.elementAt(i);
                if (!idBlock->isEmpty()) {
                    Transliterator* temp = createInstance(*idBlock, UTRANS_FORWARD, parseError, status);
                    if (U_FAILURE(status)) {
                        delete temp;
                        return nullptr;
                    }
                    if (temp != NULL && typeid(*temp) != typeid(NullTransliterator)) {
                        transliterators.addElement(temp, status);
                        if (U_FAILURE(status)) {
                            delete temp;
                            return nullptr;
                        }
                    } else {
                        delete temp;
                    }
                }
            }
            if (!parser.dataVector.isEmpty()) {
                TransliterationRuleData* data = (TransliterationRuleData*)parser.dataVector.orphanElementAt(0);
                // TODO: Should passNumber be turned into a decimal-string representation (1 -> "1")?
                RuleBasedTransliterator* temprbt = new RuleBasedTransliterator(UnicodeString(CompoundTransliterator::PASS_STRING) + UnicodeString(passNumber++),
                        data, TRUE);
                // Check if NULL before adding it to transliterators to avoid future usage of NULL pointer.
                if (temprbt == NULL) {
                    if (U_SUCCESS(status)) {
                        status = U_MEMORY_ALLOCATION_ERROR;
                    }
                    return t;
                }
                transliterators.addElement(temprbt, status);
                if (U_FAILURE(status)) {
                    delete temprbt;
                    return t;
                }
                // TODO: ICU-21701 the transliterators vector will leak its contents if anything goes wrong.
                //       Under normal operation, the CompoundTransliterator constructor adopts the
                //       the contents of the vector.
            }
        }

        t = new CompoundTransliterator(transliterators, passNumber - 1, parseError, status);
        // Null pointer check
        if (t != NULL) {
            t->setID(ID);
            t->adoptFilter(parser.orphanCompoundFilter());
        }
    }
    if (U_SUCCESS(status) && t == NULL) {
        status = U_MEMORY_ALLOCATION_ERROR;
    }
    return t;
}

UnicodeString& Transliterator::toRules(UnicodeString& rulesSource,
                                       UBool escapeUnprintable) const {
    // The base class implementation of toRules munges the ID into
    // the correct format.  That is: foo => ::foo
    if (escapeUnprintable) {
        rulesSource.truncate(0);
        UnicodeString id = getID();
        for (int32_t i=0; i<id.length();) {
            UChar32 c = id.char32At(i);
            if (!ICU_Utility::escapeUnprintable(rulesSource, c)) {
                rulesSource.append(c);
            }
            i += U16_LENGTH(c);
        }
    } else {
        rulesSource = getID();
    }
    // KEEP in sync with rbt_pars
    rulesSource.insert(0, UNICODE_STRING_SIMPLE("::"));
    rulesSource.append(ID_DELIM);
    return rulesSource;
}

int32_t Transliterator::countElements() const {
    const CompoundTransliterator* ct = dynamic_cast<const CompoundTransliterator*>(this);
    return ct != NULL ? ct->getCount() : 0;
}

const Transliterator& Transliterator::getElement(int32_t index, UErrorCode& ec) const {
    if (U_FAILURE(ec)) {
        return *this;
    }
    const CompoundTransliterator* cpd = dynamic_cast<const CompoundTransliterator*>(this);
    int32_t n = (cpd == NULL) ? 1 : cpd->getCount();
    if (index < 0 || index >= n) {
        ec = U_INDEX_OUTOFBOUNDS_ERROR;
        return *this;
    } else {
        return (n == 1) ? *this : cpd->getTransliterator(index);
    }
}

UnicodeSet& Transliterator::getSourceSet(UnicodeSet& result) const {
    handleGetSourceSet(result);
    if (filter != NULL) {
        UnicodeSet* filterSet = dynamic_cast<UnicodeSet*>(filter);
        UBool deleteFilterSet = FALSE;
        // Most, but not all filters will be UnicodeSets.  Optimize for
        // the high-runner case.
        if (filterSet == NULL) {
            filterSet = new UnicodeSet();
            // Check null pointer
            if (filterSet == NULL) {
                return result;
            }
            deleteFilterSet = TRUE;
            filter->addMatchSetTo(*filterSet);
        }
        result.retainAll(*filterSet);
        if (deleteFilterSet) {
            delete filterSet;
        }
    }
    return result;
}

void Transliterator::handleGetSourceSet(UnicodeSet& result) const {
    result.clear();
}

UnicodeSet& Transliterator::getTargetSet(UnicodeSet& result) const {
    return result.clear();
}

// For public consumption
void U_EXPORT2 Transliterator::registerFactory(const UnicodeString& id,
                                     Transliterator::Factory factory,
                                     Transliterator::Token context) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        _registerFactory(id, factory, context);
    }
}

// To be called only by Transliterator subclasses that are called
// to register themselves by initializeRegistry().
void Transliterator::_registerFactory(const UnicodeString& id,
                                      Transliterator::Factory factory,
                                      Transliterator::Token context) {
    UErrorCode ec = U_ZERO_ERROR;
    registry->put(id, factory, context, TRUE, ec);
}

// To be called only by Transliterator subclasses that are called
// to register themselves by initializeRegistry().
void Transliterator::_registerSpecialInverse(const UnicodeString& target,
                                             const UnicodeString& inverseTarget,
                                             UBool bidirectional) {
    UErrorCode status = U_ZERO_ERROR;
    TransliteratorIDParser::registerSpecialInverse(target, inverseTarget, bidirectional, status);
}

/**
 * Registers a instance <tt>obj</tt> of a subclass of
 * <code>Transliterator</code> with the system.  This object must
 * implement the <tt>clone()</tt> method.  When
 * <tt>getInstance()</tt> is called with an ID string that is
 * equal to <tt>obj.getID()</tt>, then <tt>obj.clone()</tt> is
 * returned.
 *
 * @param obj an instance of subclass of
 * <code>Transliterator</code> that defines <tt>clone()</tt>
 * @see #getInstance
 * @see #unregister
 */
void U_EXPORT2 Transliterator::registerInstance(Transliterator* adoptedPrototype) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        _registerInstance(adoptedPrototype);
    }
}

void Transliterator::_registerInstance(Transliterator* adoptedPrototype) {
    UErrorCode ec = U_ZERO_ERROR;
    registry->put(adoptedPrototype, TRUE, ec);
}

void U_EXPORT2 Transliterator::registerAlias(const UnicodeString& aliasID,
                                             const UnicodeString& realID) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        _registerAlias(aliasID, realID);
    }
}

void Transliterator::_registerAlias(const UnicodeString& aliasID,
                                    const UnicodeString& realID) {
    UErrorCode ec = U_ZERO_ERROR;
    registry->put(aliasID, realID, FALSE, TRUE, ec);
}

/**
 * Unregisters a transliterator or class.  This may be either
 * a system transliterator or a user transliterator or class.
 * 
 * @param ID the ID of the transliterator or class
 * @see #registerInstance

 */
void U_EXPORT2 Transliterator::unregister(const UnicodeString& ID) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        registry->remove(ID);
    }
}

/**
 * == OBSOLETE - remove in ICU 3.4 ==
 * Return the number of IDs currently registered with the system.
 * To retrieve the actual IDs, call getAvailableID(i) with
 * i from 0 to countAvailableIDs() - 1.
 */
int32_t U_EXPORT2 Transliterator::countAvailableIDs(void) {
    int32_t retVal = 0;
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        retVal = registry->countAvailableIDs();
    }
    return retVal;
}

/**
 * == OBSOLETE - remove in ICU 3.4 ==
 * Return the index-th available ID.  index must be between 0
 * and countAvailableIDs() - 1, inclusive.  If index is out of
 * range, the result of getAvailableID(0) is returned.
 */
const UnicodeString& U_EXPORT2 Transliterator::getAvailableID(int32_t index) {
    const UnicodeString* result = NULL;
    umtx_lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        result = &registry->getAvailableID(index);
    }
    umtx_unlock(&registryMutex);
    U_ASSERT(result != NULL); // fail if no registry
    return *result;
}

StringEnumeration* U_EXPORT2 Transliterator::getAvailableIDs(UErrorCode& ec) {
    if (U_FAILURE(ec)) return NULL;
    StringEnumeration* result = NULL;
    umtx_lock(&registryMutex);
    if (HAVE_REGISTRY(ec)) {
        result = registry->getAvailableIDs();
    }
    umtx_unlock(&registryMutex);
    if (result == NULL) {
        ec = U_INTERNAL_TRANSLITERATOR_ERROR;
    }
    return result;
}

int32_t U_EXPORT2 Transliterator::countAvailableSources(void) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    return HAVE_REGISTRY(ec) ? _countAvailableSources() : 0;
}

UnicodeString& U_EXPORT2 Transliterator::getAvailableSource(int32_t index,
                                                  UnicodeString& result) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        _getAvailableSource(index, result);
    }
    return result;
}

int32_t U_EXPORT2 Transliterator::countAvailableTargets(const UnicodeString& source) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    return HAVE_REGISTRY(ec) ? _countAvailableTargets(source) : 0;
}

UnicodeString& U_EXPORT2 Transliterator::getAvailableTarget(int32_t index,
                                                  const UnicodeString& source,
                                                  UnicodeString& result) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        _getAvailableTarget(index, source, result);
    }
    return result;
}

int32_t U_EXPORT2 Transliterator::countAvailableVariants(const UnicodeString& source,
                                               const UnicodeString& target) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    return HAVE_REGISTRY(ec) ? _countAvailableVariants(source, target) : 0;
}

UnicodeString& U_EXPORT2 Transliterator::getAvailableVariant(int32_t index,
                                                   const UnicodeString& source,
                                                   const UnicodeString& target,
                                                   UnicodeString& result) {
    Mutex lock(&registryMutex);
    UErrorCode ec = U_ZERO_ERROR;
    if (HAVE_REGISTRY(ec)) {
        _getAvailableVariant(index, source, target, result);
    }
    return result;
}

int32_t Transliterator::_countAvailableSources(void) {
    return registry->countAvailableSources();
}

UnicodeString& Transliterator::_getAvailableSource(int32_t index,
                                                  UnicodeString& result) {
    return registry->getAvailableSource(index, result);
}

int32_t Transliterator::_countAvailableTargets(const UnicodeString& source) {
    return registry->countAvailableTargets(source);
}

UnicodeString& Transliterator::_getAvailableTarget(int32_t index,
                                                  const UnicodeString& source,
                                                  UnicodeString& result) {
    return registry->getAvailableTarget(index, source, result);
}

int32_t Transliterator::_countAvailableVariants(const UnicodeString& source,
                                               const UnicodeString& target) {
    return registry->countAvailableVariants(source, target);
}

UnicodeString& Transliterator::_getAvailableVariant(int32_t index,
                                                   const UnicodeString& source,
                                                   const UnicodeString& target,
                                                   UnicodeString& result) {
    return registry->getAvailableVariant(index, source, target, result);
}

#ifdef U_USE_DEPRECATED_TRANSLITERATOR_API

/**
 * Method for subclasses to use to obtain a character in the given
 * string, with filtering.
 * @deprecated the new architecture provides filtering at the top
 * level.  This method will be removed Dec 31 2001.
 */
UChar Transliterator::filteredCharAt(const Replaceable& text, int32_t i) const {
    UChar c;
    const UnicodeFilter* localFilter = getFilter();
    return (localFilter == 0) ? text.charAt(i) :
        (localFilter->contains(c = text.charAt(i)) ? c : (UChar)0xFFFE);
}

#endif

/**
 * If the registry is initialized, return TRUE.  If not, initialize it
 * and return TRUE.  If the registry cannot be initialized, return
 * FALSE (rare).
 *
 * IMPORTANT: Upon entry, registryMutex must be LOCKED.  The entire
 * initialization is done with the lock held.  There is NO REASON to
 * unlock, since no other thread that is waiting on the registryMutex
 * cannot itself proceed until the registry is initialized.
 */
UBool Transliterator::initializeRegistry(UErrorCode &status) {
    if (registry != 0) {
        return TRUE;
    }

    registry = new TransliteratorRegistry(status);
    if (registry == 0 || U_FAILURE(status)) {
        delete registry;
        registry = 0;
        return FALSE; // can't create registry, no recovery
    }

    /* The following code parses the index table located in
     * icu/data/translit/root.txt.  The index is an n x 4 table
     * that follows this format:
     *  <id>{
     *      file{
     *          resource{"<resource>"}
     *          direction{"<direction>"}
     *      }
     *  }
     *  <id>{
     *      internal{
     *          resource{"<resource>"}
     *          direction{"<direction"}
     *       }
     *  }
     *  <id>{
     *      alias{"<getInstanceArg"}
     *  }
     * <id> is the ID of the system transliterator being defined.  These
     * are public IDs enumerated by Transliterator.getAvailableIDs(),
     * unless the second field is "internal".
     * 
     * <resource> is a ResourceReader resource name.  Currently these refer
     * to file names under com/ibm/text/resources.  This string is passed
     * directly to ResourceReader, together with <encoding>.
     * 
     * <direction> is either "FORWARD" or "REVERSE".
     * 
     * <getInstanceArg> is a string to be passed directly to
     * Transliterator.getInstance().  The returned Transliterator object
     * then has its ID changed to <id> and is returned.
     *
     * The extra blank field on "alias" lines is to make the array square.
     */
    //static const char translit_index[] = "translit_index";

    UErrorCode lstatus = U_ZERO_ERROR;
    UResourceBundle *bundle, *transIDs, *colBund;
    bundle = ures_open(U_ICUDATA_TRANSLIT, NULL/*open default locale*/, &lstatus);
    transIDs = ures_getByKey(bundle, RB_RULE_BASED_IDS, 0, &lstatus);
    const UnicodeString T_PART = UNICODE_STRING_SIMPLE("-t-");

    int32_t row, maxRows;
    if (lstatus == U_MEMORY_ALLOCATION_ERROR) {
        delete registry;
        registry = nullptr;
        status = U_MEMORY_ALLOCATION_ERROR;
        return FALSE;
    }
    if (U_SUCCESS(lstatus)) {
        maxRows = ures_getSize(transIDs);
        for (row = 0; row < maxRows; row++) {
            colBund = ures_getByIndex(transIDs, row, 0, &lstatus);
            if (U_SUCCESS(lstatus)) {
                UnicodeString id(ures_getKey(colBund), -1, US_INV);
                if(id.indexOf(T_PART) != -1) {
                    ures_close(colBund);
                    continue;
                }
                UResourceBundle* res = ures_getNextResource(colBund, NULL, &lstatus);
                const char* typeStr = ures_getKey(res);
                UChar type;
                u_charsToUChars(typeStr, &type, 1);

                if (U_SUCCESS(lstatus)) {
                    int32_t len = 0;
                    const UChar *resString;
                    switch (type) {
                    case 0x66: // 'f'
                    case 0x69: // 'i'
                        // 'file' or 'internal';
                        // row[2]=resource, row[3]=direction
                        {
                            
                            resString = ures_getStringByKey(res, "resource", &len, &lstatus);
                            UBool visible = (type == 0x0066 /*f*/);
                            UTransDirection dir = 
                                (ures_getUnicodeStringByKey(res, "direction", &lstatus).charAt(0) ==
                                 0x0046 /*F*/) ?
                                UTRANS_FORWARD : UTRANS_REVERSE;
                            registry->put(id, UnicodeString(TRUE, resString, len), dir, TRUE, visible, lstatus);
                        }
                        break;
                    case 0x61: // 'a'
                        // 'alias'; row[2]=createInstance argument
                        resString = ures_getString(res, &len, &lstatus);
                        registry->put(id, UnicodeString(TRUE, resString, len), TRUE, TRUE, lstatus);
                        break;
                    }
                }
                ures_close(res);
            }
            ures_close(colBund);
        }
    }

    ures_close(transIDs);
    ures_close(bundle);

    // Manually add prototypes that the system knows about to the
    // cache.  This is how new non-rule-based transliterators are
    // added to the system.
    
    // This is to allow for null pointer check
    NullTransliterator* tempNullTranslit = new NullTransliterator();
    LowercaseTransliterator* tempLowercaseTranslit = new LowercaseTransliterator();
    UppercaseTransliterator* tempUppercaseTranslit = new UppercaseTransliterator();
    TitlecaseTransliterator* tempTitlecaseTranslit = new TitlecaseTransliterator();
    UnicodeNameTransliterator* tempUnicodeTranslit = new UnicodeNameTransliterator();
    NameUnicodeTransliterator* tempNameUnicodeTranslit = new NameUnicodeTransliterator();
#if !UCONFIG_NO_BREAK_ITERATION
     // TODO: could or should these transliterators be referenced polymorphically once constructed?
     BreakTransliterator* tempBreakTranslit         = new BreakTransliterator();
#endif
    // Check for null pointers
    if (tempNullTranslit == NULL || tempLowercaseTranslit == NULL || tempUppercaseTranslit == NULL ||
        tempTitlecaseTranslit == NULL || tempUnicodeTranslit == NULL || 
#if !UCONFIG_NO_BREAK_ITERATION
        tempBreakTranslit == NULL ||
#endif
        tempNameUnicodeTranslit == NULL )
    {
        delete tempNullTranslit;
        delete tempLowercaseTranslit;
        delete tempUppercaseTranslit;
        delete tempTitlecaseTranslit;
        delete tempUnicodeTranslit;
        delete tempNameUnicodeTranslit;
#if !UCONFIG_NO_BREAK_ITERATION
        delete tempBreakTranslit;
#endif
        // Since there was an error, remove registry
        delete registry;
        registry = NULL;

        status = U_MEMORY_ALLOCATION_ERROR;
        return 0;
    }

    registry->put(tempNullTranslit, TRUE, status);
    registry->put(tempLowercaseTranslit, TRUE, status);
    registry->put(tempUppercaseTranslit, TRUE, status);
    registry->put(tempTitlecaseTranslit, TRUE, status);
    registry->put(tempUnicodeTranslit, TRUE, status);
    registry->put(tempNameUnicodeTranslit, TRUE, status);
#if !UCONFIG_NO_BREAK_ITERATION
    registry->put(tempBreakTranslit, FALSE, status);   // FALSE means invisible.
#endif

    RemoveTransliterator::registerIDs(); // Must be within mutex
    EscapeTransliterator::registerIDs();
    UnescapeTransliterator::registerIDs();
    NormalizationTransliterator::registerIDs();
    AnyTransliterator::registerIDs();

    _registerSpecialInverse(UNICODE_STRING_SIMPLE("Null"),
                            UNICODE_STRING_SIMPLE("Null"), FALSE);
    _registerSpecialInverse(UNICODE_STRING_SIMPLE("Upper"),
                            UNICODE_STRING_SIMPLE("Lower"), TRUE);
    _registerSpecialInverse(UNICODE_STRING_SIMPLE("Title"),
                            UNICODE_STRING_SIMPLE("Lower"), FALSE);

    ucln_i18n_registerCleanup(UCLN_I18N_TRANSLITERATOR, utrans_transliterator_cleanup);

    return TRUE;
}

U_NAMESPACE_END

// Defined in transreg.h:

/**
 * Release all static memory held by transliterator.  This will
 * necessarily invalidate any rule-based transliterators held by the
 * user, because RBTs hold pointers to common data objects.
 */
U_CFUNC UBool utrans_transliterator_cleanup(void) {
    U_NAMESPACE_USE
    TransliteratorIDParser::cleanup();
    if (registry) {
        delete registry;
        registry = NULL;
    }
    return TRUE;
}

#endif /* #if !UCONFIG_NO_TRANSLITERATION */

//eof