summaryrefslogtreecommitdiff
path: root/deps/icu-small/source/common/bmpset.cpp
blob: f84bfd7f5bfcf1044aff8e349226cd04c24f0f59 (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
// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
******************************************************************************
*
*   Copyright (C) 2007-2012, International Business Machines
*   Corporation and others.  All Rights Reserved.
*
******************************************************************************
*   file name:  bmpset.cpp
*   encoding:   UTF-8
*   tab size:   8 (not used)
*   indentation:4
*
*   created on: 2007jan29
*   created by: Markus W. Scherer
*/

#include "unicode/utypes.h"
#include "unicode/uniset.h"
#include "unicode/utf8.h"
#include "unicode/utf16.h"
#include "cmemory.h"
#include "bmpset.h"
#include "uassert.h"

U_NAMESPACE_BEGIN

BMPSet::BMPSet(const int32_t *parentList, int32_t parentListLength) :
        list(parentList), listLength(parentListLength) {
    uprv_memset(latin1Contains, 0, sizeof(latin1Contains));
    uprv_memset(table7FF, 0, sizeof(table7FF));
    uprv_memset(bmpBlockBits, 0, sizeof(bmpBlockBits));

    /*
     * Set the list indexes for binary searches for
     * U+0800, U+1000, U+2000, .., U+F000, U+10000.
     * U+0800 is the first 3-byte-UTF-8 code point. Lower code points are
     * looked up in the bit tables.
     * The last pair of indexes is for finding supplementary code points.
     */
    list4kStarts[0]=findCodePoint(0x800, 0, listLength-1);
    int32_t i;
    for(i=1; i<=0x10; ++i) {
        list4kStarts[i]=findCodePoint(i<<12, list4kStarts[i-1], listLength-1);
    }
    list4kStarts[0x11]=listLength-1;
    containsFFFD=containsSlow(0xfffd, list4kStarts[0xf], list4kStarts[0x10]);

    initBits();
    overrideIllegal();
}

BMPSet::BMPSet(const BMPSet &otherBMPSet, const int32_t *newParentList, int32_t newParentListLength) :
        containsFFFD(otherBMPSet.containsFFFD),
        list(newParentList), listLength(newParentListLength) {
    uprv_memcpy(latin1Contains, otherBMPSet.latin1Contains, sizeof(latin1Contains));
    uprv_memcpy(table7FF, otherBMPSet.table7FF, sizeof(table7FF));
    uprv_memcpy(bmpBlockBits, otherBMPSet.bmpBlockBits, sizeof(bmpBlockBits));
    uprv_memcpy(list4kStarts, otherBMPSet.list4kStarts, sizeof(list4kStarts));
}

BMPSet::~BMPSet() {
}

/*
 * Set bits in a bit rectangle in "vertical" bit organization.
 * start<limit<=0x800
 */
static void set32x64Bits(uint32_t table[64], int32_t start, int32_t limit) {
    U_ASSERT(start<limit);
    U_ASSERT(limit<=0x800);

    int32_t lead=start>>6;  // Named for UTF-8 2-byte lead byte with upper 5 bits.
    int32_t trail=start&0x3f;  // Named for UTF-8 2-byte trail byte with lower 6 bits.

    // Set one bit indicating an all-one block.
    uint32_t bits=(uint32_t)1<<lead;
    if((start+1)==limit) {  // Single-character shortcut.
        table[trail]|=bits;
        return;
    }

    int32_t limitLead=limit>>6;
    int32_t limitTrail=limit&0x3f;

    if(lead==limitLead) {
        // Partial vertical bit column.
        while(trail<limitTrail) {
            table[trail++]|=bits;
        }
    } else {
        // Partial vertical bit column,
        // followed by a bit rectangle,
        // followed by another partial vertical bit column.
        if(trail>0) {
            do {
                table[trail++]|=bits;
            } while(trail<64);
            ++lead;
        }
        if(lead<limitLead) {
            bits=~((1<<lead)-1);
            if(limitLead<0x20) {
                bits&=(1<<limitLead)-1;
            }
            for(trail=0; trail<64; ++trail) {
                table[trail]|=bits;
            }
        }
        // limit<=0x800. If limit==0x800 then limitLead=32 and limitTrail=0.
        // In that case, bits=1<<limitLead is undefined but the bits value
        // is not used because trail<limitTrail is already false.
        bits=(uint32_t)1<<((limitLead == 0x20) ? (limitLead - 1) : limitLead);
        for(trail=0; trail<limitTrail; ++trail) {
            table[trail]|=bits;
        }
    }
}

void BMPSet::initBits() {
    UChar32 start, limit;
    int32_t listIndex=0;

    // Set latin1Contains[].
    do {
        start=list[listIndex++];
        if(listIndex<listLength) {
            limit=list[listIndex++];
        } else {
            limit=0x110000;
        }
        if(start>=0x100) {
            break;
        }
        do {
            latin1Contains[start++]=1;
        } while(start<limit && start<0x100);
    } while(limit<=0x100);

    // Find the first range overlapping with (or after) 80..FF again,
    // to include them in table7FF as well.
    for(listIndex=0;;) {
        start=list[listIndex++];
        if(listIndex<listLength) {
            limit=list[listIndex++];
        } else {
            limit=0x110000;
        }
        if(limit>0x80) {
            if(start<0x80) {
                start=0x80;
            }
            break;
        }
    }

    // Set table7FF[].
    while(start<0x800) {
        set32x64Bits(table7FF, start, limit<=0x800 ? limit : 0x800);
        if(limit>0x800) {
            start=0x800;
            break;
        }

        start=list[listIndex++];
        if(listIndex<listLength) {
            limit=list[listIndex++];
        } else {
            limit=0x110000;
        }
    }

    // Set bmpBlockBits[].
    int32_t minStart=0x800;
    while(start<0x10000) {
        if(limit>0x10000) {
            limit=0x10000;
        }

        if(start<minStart) {
            start=minStart;
        }
        if(start<limit) {  // Else: Another range entirely in a known mixed-value block.
            if(start&0x3f) {
                // Mixed-value block of 64 code points.
                start>>=6;
                bmpBlockBits[start&0x3f]|=0x10001<<(start>>6);
                start=(start+1)<<6;  // Round up to the next block boundary.
                minStart=start;      // Ignore further ranges in this block.
            }
            if(start<limit) {
                if(start<(limit&~0x3f)) {
                    // Multiple all-ones blocks of 64 code points each.
                    set32x64Bits(bmpBlockBits, start>>6, limit>>6);
                }

                if(limit&0x3f) {
                    // Mixed-value block of 64 code points.
                    limit>>=6;
                    bmpBlockBits[limit&0x3f]|=0x10001<<(limit>>6);
                    limit=(limit+1)<<6;  // Round up to the next block boundary.
                    minStart=limit;      // Ignore further ranges in this block.
                }
            }
        }

        if(limit==0x10000) {
            break;
        }

        start=list[listIndex++];
        if(listIndex<listLength) {
            limit=list[listIndex++];
        } else {
            limit=0x110000;
        }
    }
}

/*
 * Override some bits and bytes to the result of contains(FFFD)
 * for faster validity checking at runtime.
 * No need to set 0 values where they were reset to 0 in the constructor
 * and not modified by initBits().
 * (table7FF[] 0..7F, bmpBlockBits[] 0..7FF)
 * Need to set 0 values for surrogates D800..DFFF.
 */
void BMPSet::overrideIllegal() {
    uint32_t bits, mask;
    int32_t i;

    if(containsFFFD) {
        bits=3;                 // Lead bytes 0xC0 and 0xC1.
        for(i=0; i<64; ++i) {
            table7FF[i]|=bits;
        }

        bits=1;                 // Lead byte 0xE0.
        for(i=0; i<32; ++i) {   // First half of 4k block.
            bmpBlockBits[i]|=bits;
        }

        mask=~(0x10001<<0xd);   // Lead byte 0xED.
        bits=1<<0xd;
        for(i=32; i<64; ++i) {  // Second half of 4k block.
            bmpBlockBits[i]=(bmpBlockBits[i]&mask)|bits;
        }
    } else {
        mask=~(0x10001<<0xd);   // Lead byte 0xED.
        for(i=32; i<64; ++i) {  // Second half of 4k block.
            bmpBlockBits[i]&=mask;
        }
    }
}

int32_t BMPSet::findCodePoint(UChar32 c, int32_t lo, int32_t hi) const {
    /* Examples:
                                       findCodePoint(c)
       set              list[]         c=0 1 3 4 7 8
       ===              ==============   ===========
       []               [110000]         0 0 0 0 0 0
       [\u0000-\u0003]  [0, 4, 110000]   1 1 1 2 2 2
       [\u0004-\u0007]  [4, 8, 110000]   0 0 0 1 1 2
       [:Any:]          [0, 110000]      1 1 1 1 1 1
     */

    // Return the smallest i such that c < list[i].  Assume
    // list[len - 1] == HIGH and that c is legal (0..HIGH-1).
    if (c < list[lo])
        return lo;
    // High runner test.  c is often after the last range, so an
    // initial check for this condition pays off.
    if (lo >= hi || c >= list[hi-1])
        return hi;
    // invariant: c >= list[lo]
    // invariant: c < list[hi]
    for (;;) {
        int32_t i = (lo + hi) >> 1;
        if (i == lo) {
            break; // Found!
        } else if (c < list[i]) {
            hi = i;
        } else {
            lo = i;
        }
    }
    return hi;
}

UBool
BMPSet::contains(UChar32 c) const {
    if((uint32_t)c<=0xff) {
        return (UBool)latin1Contains[c];
    } else if((uint32_t)c<=0x7ff) {
        return (UBool)((table7FF[c&0x3f]&((uint32_t)1<<(c>>6)))!=0);
    } else if((uint32_t)c<0xd800 || (c>=0xe000 && c<=0xffff)) {
        int lead=c>>12;
        uint32_t twoBits=(bmpBlockBits[(c>>6)&0x3f]>>lead)&0x10001;
        if(twoBits<=1) {
            // All 64 code points with the same bits 15..6
            // are either in the set or not.
            return (UBool)twoBits;
        } else {
            // Look up the code point in its 4k block of code points.
            return containsSlow(c, list4kStarts[lead], list4kStarts[lead+1]);
        }
    } else if((uint32_t)c<=0x10ffff) {
        // surrogate or supplementary code point
        return containsSlow(c, list4kStarts[0xd], list4kStarts[0x11]);
    } else {
        // Out-of-range code points get FALSE, consistent with long-standing
        // behavior of UnicodeSet::contains(c).
        return FALSE;
    }
}

/*
 * Check for sufficient length for trail unit for each surrogate pair.
 * Handle single surrogates as surrogate code points as usual in ICU.
 */
const UChar *
BMPSet::span(const UChar *s, const UChar *limit, USetSpanCondition spanCondition) const {
    UChar c, c2;

    if(spanCondition) {
        // span
        do {
            c=*s;
            if(c<=0xff) {
                if(!latin1Contains[c]) {
                    break;
                }
            } else if(c<=0x7ff) {
                if((table7FF[c&0x3f]&((uint32_t)1<<(c>>6)))==0) {
                    break;
                }
            } else if(c<0xd800 || c>=0xe000) {
                int lead=c>>12;
                uint32_t twoBits=(bmpBlockBits[(c>>6)&0x3f]>>lead)&0x10001;
                if(twoBits<=1) {
                    // All 64 code points with the same bits 15..6
                    // are either in the set or not.
                    if(twoBits==0) {
                        break;
                    }
                } else {
                    // Look up the code point in its 4k block of code points.
                    if(!containsSlow(c, list4kStarts[lead], list4kStarts[lead+1])) {
                        break;
                    }
                }
            } else if(c>=0xdc00 || (s+1)==limit || (c2=s[1])<0xdc00 || c2>=0xe000) {
                // surrogate code point
                if(!containsSlow(c, list4kStarts[0xd], list4kStarts[0xe])) {
                    break;
                }
            } else {
                // surrogate pair
                if(!containsSlow(U16_GET_SUPPLEMENTARY(c, c2), list4kStarts[0x10], list4kStarts[0x11])) {
                    break;
                }
                ++s;
            }
        } while(++s<limit);
    } else {
        // span not
        do {
            c=*s;
            if(c<=0xff) {
                if(latin1Contains[c]) {
                    break;
                }
            } else if(c<=0x7ff) {
                if((table7FF[c&0x3f]&((uint32_t)1<<(c>>6)))!=0) {
                    break;
                }
            } else if(c<0xd800 || c>=0xe000) {
                int lead=c>>12;
                uint32_t twoBits=(bmpBlockBits[(c>>6)&0x3f]>>lead)&0x10001;
                if(twoBits<=1) {
                    // All 64 code points with the same bits 15..6
                    // are either in the set or not.
                    if(twoBits!=0) {
                        break;
                    }
                } else {
                    // Look up the code point in its 4k block of code points.
                    if(containsSlow(c, list4kStarts[lead], list4kStarts[lead+1])) {
                        break;
                    }
                }
            } else if(c>=0xdc00 || (s+1)==limit || (c2=s[1])<0xdc00 || c2>=0xe000) {
                // surrogate code point
                if(containsSlow(c, list4kStarts[0xd], list4kStarts[0xe])) {
                    break;
                }
            } else {
                // surrogate pair
                if(containsSlow(U16_GET_SUPPLEMENTARY(c, c2), list4kStarts[0x10], list4kStarts[0x11])) {
                    break;
                }
                ++s;
            }
        } while(++s<limit);
    }
    return s;
}

/* Symmetrical with span(). */
const UChar *
BMPSet::spanBack(const UChar *s, const UChar *limit, USetSpanCondition spanCondition) const {
    UChar c, c2;

    if(spanCondition) {
        // span
        for(;;) {
            c=*(--limit);
            if(c<=0xff) {
                if(!latin1Contains[c]) {
                    break;
                }
            } else if(c<=0x7ff) {
                if((table7FF[c&0x3f]&((uint32_t)1<<(c>>6)))==0) {
                    break;
                }
            } else if(c<0xd800 || c>=0xe000) {
                int lead=c>>12;
                uint32_t twoBits=(bmpBlockBits[(c>>6)&0x3f]>>lead)&0x10001;
                if(twoBits<=1) {
                    // All 64 code points with the same bits 15..6
                    // are either in the set or not.
                    if(twoBits==0) {
                        break;
                    }
                } else {
                    // Look up the code point in its 4k block of code points.
                    if(!containsSlow(c, list4kStarts[lead], list4kStarts[lead+1])) {
                        break;
                    }
                }
            } else if(c<0xdc00 || s==limit || (c2=*(limit-1))<0xd800 || c2>=0xdc00) {
                // surrogate code point
                if(!containsSlow(c, list4kStarts[0xd], list4kStarts[0xe])) {
                    break;
                }
            } else {
                // surrogate pair
                if(!containsSlow(U16_GET_SUPPLEMENTARY(c2, c), list4kStarts[0x10], list4kStarts[0x11])) {
                    break;
                }
                --limit;
            }
            if(s==limit) {
                return s;
            }
        }
    } else {
        // span not
        for(;;) {
            c=*(--limit);
            if(c<=0xff) {
                if(latin1Contains[c]) {
                    break;
                }
            } else if(c<=0x7ff) {
                if((table7FF[c&0x3f]&((uint32_t)1<<(c>>6)))!=0) {
                    break;
                }
            } else if(c<0xd800 || c>=0xe000) {
                int lead=c>>12;
                uint32_t twoBits=(bmpBlockBits[(c>>6)&0x3f]>>lead)&0x10001;
                if(twoBits<=1) {
                    // All 64 code points with the same bits 15..6
                    // are either in the set or not.
                    if(twoBits!=0) {
                        break;
                    }
                } else {
                    // Look up the code point in its 4k block of code points.
                    if(containsSlow(c, list4kStarts[lead], list4kStarts[lead+1])) {
                        break;
                    }
                }
            } else if(c<0xdc00 || s==limit || (c2=*(limit-1))<0xd800 || c2>=0xdc00) {
                // surrogate code point
                if(containsSlow(c, list4kStarts[0xd], list4kStarts[0xe])) {
                    break;
                }
            } else {
                // surrogate pair
                if(containsSlow(U16_GET_SUPPLEMENTARY(c2, c), list4kStarts[0x10], list4kStarts[0x11])) {
                    break;
                }
                --limit;
            }
            if(s==limit) {
                return s;
            }
        }
    }
    return limit+1;
}

/*
 * Precheck for sufficient trail bytes at end of string only once per span.
 * Check validity.
 */
const uint8_t *
BMPSet::spanUTF8(const uint8_t *s, int32_t length, USetSpanCondition spanCondition) const {
    const uint8_t *limit=s+length;
    uint8_t b=*s;
    if(U8_IS_SINGLE(b)) {
        // Initial all-ASCII span.
        if(spanCondition) {
            do {
                if(!latin1Contains[b] || ++s==limit) {
                    return s;
                }
                b=*s;
            } while(U8_IS_SINGLE(b));
        } else {
            do {
                if(latin1Contains[b] || ++s==limit) {
                    return s;
                }
                b=*s;
            } while(U8_IS_SINGLE(b));
        }
        length=(int32_t)(limit-s);
    }

    if(spanCondition!=USET_SPAN_NOT_CONTAINED) {
        spanCondition=USET_SPAN_CONTAINED;  // Pin to 0/1 values.
    }

    const uint8_t *limit0=limit;

    /*
     * Make sure that the last 1/2/3/4-byte sequence before limit is complete
     * or runs into a lead byte.
     * In the span loop compare s with limit only once
     * per multi-byte character.
     *
     * Give a trailing illegal sequence the same value as the result of contains(FFFD),
     * including it if that is part of the span, otherwise set limit0 to before
     * the truncated sequence.
     */
    b=*(limit-1);
    if((int8_t)b<0) {
        // b>=0x80: lead or trail byte
        if(b<0xc0) {
            // single trail byte, check for preceding 3- or 4-byte lead byte
            if(length>=2 && (b=*(limit-2))>=0xe0) {
                limit-=2;
                if(containsFFFD!=spanCondition) {
                    limit0=limit;
                }
            } else if(b<0xc0 && b>=0x80 && length>=3 && (b=*(limit-3))>=0xf0) {
                // 4-byte lead byte with only two trail bytes
                limit-=3;
                if(containsFFFD!=spanCondition) {
                    limit0=limit;
                }
            }
        } else {
            // lead byte with no trail bytes
            --limit;
            if(containsFFFD!=spanCondition) {
                limit0=limit;
            }
        }
    }

    uint8_t t1, t2, t3;

    while(s<limit) {
        b=*s;
        if(U8_IS_SINGLE(b)) {
            // ASCII
            if(spanCondition) {
                do {
                    if(!latin1Contains[b]) {
                        return s;
                    } else if(++s==limit) {
                        return limit0;
                    }
                    b=*s;
                } while(U8_IS_SINGLE(b));
            } else {
                do {
                    if(latin1Contains[b]) {
                        return s;
                    } else if(++s==limit) {
                        return limit0;
                    }
                    b=*s;
                } while(U8_IS_SINGLE(b));
            }
        }
        ++s;  // Advance past the lead byte.
        if(b>=0xe0) {
            if(b<0xf0) {
                if( /* handle U+0000..U+FFFF inline */
                    (t1=(uint8_t)(s[0]-0x80)) <= 0x3f &&
                    (t2=(uint8_t)(s[1]-0x80)) <= 0x3f
                ) {
                    b&=0xf;
                    uint32_t twoBits=(bmpBlockBits[t1]>>b)&0x10001;
                    if(twoBits<=1) {
                        // All 64 code points with this lead byte and middle trail byte
                        // are either in the set or not.
                        if(twoBits!=(uint32_t)spanCondition) {
                            return s-1;
                        }
                    } else {
                        // Look up the code point in its 4k block of code points.
                        UChar32 c=(b<<12)|(t1<<6)|t2;
                        if(containsSlow(c, list4kStarts[b], list4kStarts[b+1]) != spanCondition) {
                            return s-1;
                        }
                    }
                    s+=2;
                    continue;
                }
            } else if( /* handle U+10000..U+10FFFF inline */
                (t1=(uint8_t)(s[0]-0x80)) <= 0x3f &&
                (t2=(uint8_t)(s[1]-0x80)) <= 0x3f &&
                (t3=(uint8_t)(s[2]-0x80)) <= 0x3f
            ) {
                // Give an illegal sequence the same value as the result of contains(FFFD).
                UChar32 c=((UChar32)(b-0xf0)<<18)|((UChar32)t1<<12)|(t2<<6)|t3;
                if( (   (0x10000<=c && c<=0x10ffff) ?
                            containsSlow(c, list4kStarts[0x10], list4kStarts[0x11]) :
                            containsFFFD
                    ) != spanCondition
                ) {
                    return s-1;
                }
                s+=3;
                continue;
            }
        } else {
            if( /* handle U+0000..U+07FF inline */
                b>=0xc0 &&
                (t1=(uint8_t)(*s-0x80)) <= 0x3f
            ) {
                if((USetSpanCondition)((table7FF[t1]&((uint32_t)1<<(b&0x1f)))!=0) != spanCondition) {
                    return s-1;
                }
                ++s;
                continue;
            }
        }

        // Give an illegal sequence the same value as the result of contains(FFFD).
        // Handle each byte of an illegal sequence separately to simplify the code;
        // no need to optimize error handling.
        if(containsFFFD!=spanCondition) {
            return s-1;
        }
    }

    return limit0;
}

/*
 * While going backwards through UTF-8 optimize only for ASCII.
 * Unlike UTF-16, UTF-8 is not forward-backward symmetrical, that is, it is not
 * possible to tell from the last byte in a multi-byte sequence how many
 * preceding bytes there should be. Therefore, going backwards through UTF-8
 * is much harder than going forward.
 */
int32_t
BMPSet::spanBackUTF8(const uint8_t *s, int32_t length, USetSpanCondition spanCondition) const {
    if(spanCondition!=USET_SPAN_NOT_CONTAINED) {
        spanCondition=USET_SPAN_CONTAINED;  // Pin to 0/1 values.
    }

    uint8_t b;

    do {
        b=s[--length];
        if(U8_IS_SINGLE(b)) {
            // ASCII sub-span
            if(spanCondition) {
                do {
                    if(!latin1Contains[b]) {
                        return length+1;
                    } else if(length==0) {
                        return 0;
                    }
                    b=s[--length];
                } while(U8_IS_SINGLE(b));
            } else {
                do {
                    if(latin1Contains[b]) {
                        return length+1;
                    } else if(length==0) {
                        return 0;
                    }
                    b=s[--length];
                } while(U8_IS_SINGLE(b));
            }
        }

        int32_t prev=length;
        UChar32 c;
        // trail byte: collect a multi-byte character
        // (or  lead byte in last-trail position)
        c=utf8_prevCharSafeBody(s, 0, &length, b, -3);
        // c is a valid code point, not ASCII, not a surrogate
        if(c<=0x7ff) {
            if((USetSpanCondition)((table7FF[c&0x3f]&((uint32_t)1<<(c>>6)))!=0) != spanCondition) {
                return prev+1;
            }
        } else if(c<=0xffff) {
            int lead=c>>12;
            uint32_t twoBits=(bmpBlockBits[(c>>6)&0x3f]>>lead)&0x10001;
            if(twoBits<=1) {
                // All 64 code points with the same bits 15..6
                // are either in the set or not.
                if(twoBits!=(uint32_t)spanCondition) {
                    return prev+1;
                }
            } else {
                // Look up the code point in its 4k block of code points.
                if(containsSlow(c, list4kStarts[lead], list4kStarts[lead+1]) != spanCondition) {
                    return prev+1;
                }
            }
        } else {
            if(containsSlow(c, list4kStarts[0x10], list4kStarts[0x11]) != spanCondition) {
                return prev+1;
            }
        }
    } while(length>0);
    return 0;
}

U_NAMESPACE_END