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1 // Copyright (C) 2016 and later: Unicode, Inc. and others.
2 // License & terms of use: http://www.unicode.org/copyright.html
3 /*
4 *******************************************************************************
5 *
6 *   Copyright (C) 1999-2015, International Business Machines
7 *   Corporation and others.  All Rights Reserved.
8 *
9 *******************************************************************************
10 *   file name:  utf8.h
11 *   encoding:   US-ASCII
12 *   tab size:   8 (not used)
13 *   indentation:4
14 *
15 *   created on: 1999sep13
16 *   created by: Markus W. Scherer
17 */
18 
19 /**
20  * \file
21  * \brief C API: 8-bit Unicode handling macros
22  *
23  * This file defines macros to deal with 8-bit Unicode (UTF-8) code units (bytes) and strings.
24  *
25  * For more information see utf.h and the ICU User Guide Strings chapter
26  * (http://userguide.icu-project.org/strings).
27  *
28  * <em>Usage:</em>
29  * ICU coding guidelines for if() statements should be followed when using these macros.
30  * Compound statements (curly braces {}) must be used  for if-else-while...
31  * bodies and all macro statements should be terminated with semicolon.
32  */
33 
34 #ifndef __UTF8_H__
35 #define __UTF8_H__
36 
37 #include "unicode/umachine.h"
38 #ifndef __UTF_H__
39 #   include "unicode/utf.h"
40 #endif
41 
42 /* internal definitions ----------------------------------------------------- */
43 
44 /**
45  * \var utf8_countTrailBytes
46  * Internal array with numbers of trail bytes for any given byte used in
47  * lead byte position.
48  *
49  * This is internal since it is not meant to be called directly by external clients;
50  * however it is called by public macros in this file and thus must remain stable,
51  * and should not be hidden when other internal functions are hidden (otherwise
52  * public macros would fail to compile).
53  * @internal
54  */
55 #ifdef U_UTF8_IMPL
56 U_EXPORT const uint8_t
57 #elif defined(U_STATIC_IMPLEMENTATION) || defined(U_COMMON_IMPLEMENTATION)
58 U_CFUNC const uint8_t
59 #else
60 U_CFUNC U_IMPORT const uint8_t /* U_IMPORT2? */ /*U_IMPORT*/
61 #endif
62 utf8_countTrailBytes[256];
63 
64 /**
65  * Counts the trail bytes for a UTF-8 lead byte.
66  * Returns 0 for 0..0xbf as well as for 0xfe and 0xff.
67  *
68  * This is internal since it is not meant to be called directly by external clients;
69  * however it is called by public macros in this file and thus must remain stable.
70  *
71  * Note: Beginning with ICU 50, the implementation uses a multi-condition expression
72  * which was shown in 2012 (on x86-64) to compile to fast, branch-free code.
73  * leadByte is evaluated multiple times.
74  *
75  * The pre-ICU 50 implementation used the exported array utf8_countTrailBytes:
76  * #define U8_COUNT_TRAIL_BYTES(leadByte) (utf8_countTrailBytes[leadByte])
77  * leadByte was evaluated exactly once.
78  *
79  * @param leadByte The first byte of a UTF-8 sequence. Must be 0..0xff.
80  * @internal
81  */
82 #define U8_COUNT_TRAIL_BYTES(leadByte) \
83     ((uint8_t)(leadByte)<0xf0 ? \
84         ((uint8_t)(leadByte)>=0xc0)+((uint8_t)(leadByte)>=0xe0) : \
85         (uint8_t)(leadByte)<0xfe ? 3+((uint8_t)(leadByte)>=0xf8)+((uint8_t)(leadByte)>=0xfc) : 0)
86 
87 /**
88  * Counts the trail bytes for a UTF-8 lead byte of a valid UTF-8 sequence.
89  * The maximum supported lead byte is 0xf4 corresponding to U+10FFFF.
90  * leadByte might be evaluated multiple times.
91  *
92  * This is internal since it is not meant to be called directly by external clients;
93  * however it is called by public macros in this file and thus must remain stable.
94  *
95  * @param leadByte The first byte of a UTF-8 sequence. Must be 0..0xff.
96  * @internal
97  */
98 #define U8_COUNT_TRAIL_BYTES_UNSAFE(leadByte) \
99     (((leadByte)>=0xc0)+((leadByte)>=0xe0)+((leadByte)>=0xf0))
100 
101 /**
102  * Mask a UTF-8 lead byte, leave only the lower bits that form part of the code point value.
103  *
104  * This is internal since it is not meant to be called directly by external clients;
105  * however it is called by public macros in this file and thus must remain stable.
106  * @internal
107  */
108 #define U8_MASK_LEAD_BYTE(leadByte, countTrailBytes) ((leadByte)&=(1<<(6-(countTrailBytes)))-1)
109 
110 /**
111  * Function for handling "next code point" with error-checking.
112  *
113  * This is internal since it is not meant to be called directly by external clients;
114  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
115  * file and thus must remain stable, and should not be hidden when other internal
116  * functions are hidden (otherwise public macros would fail to compile).
117  * @internal
118  */
119 U_STABLE UChar32 U_EXPORT2
120 utf8_nextCharSafeBody(const uint8_t *s, int32_t *pi, int32_t length, UChar32 c, UBool strict);
121 
122 /**
123  * Function for handling "append code point" with error-checking.
124  *
125  * This is internal since it is not meant to be called directly by external clients;
126  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
127  * file and thus must remain stable, and should not be hidden when other internal
128  * functions are hidden (otherwise public macros would fail to compile).
129  * @internal
130  */
131 U_STABLE int32_t U_EXPORT2
132 utf8_appendCharSafeBody(uint8_t *s, int32_t i, int32_t length, UChar32 c, UBool *pIsError);
133 
134 /**
135  * Function for handling "previous code point" with error-checking.
136  *
137  * This is internal since it is not meant to be called directly by external clients;
138  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
139  * file and thus must remain stable, and should not be hidden when other internal
140  * functions are hidden (otherwise public macros would fail to compile).
141  * @internal
142  */
143 U_STABLE UChar32 U_EXPORT2
144 utf8_prevCharSafeBody(const uint8_t *s, int32_t start, int32_t *pi, UChar32 c, UBool strict);
145 
146 /**
147  * Function for handling "skip backward one code point" with error-checking.
148  *
149  * This is internal since it is not meant to be called directly by external clients;
150  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
151  * file and thus must remain stable, and should not be hidden when other internal
152  * functions are hidden (otherwise public macros would fail to compile).
153  * @internal
154  */
155 U_STABLE int32_t U_EXPORT2
156 utf8_back1SafeBody(const uint8_t *s, int32_t start, int32_t i);
157 
158 /* single-code point definitions -------------------------------------------- */
159 
160 /**
161  * Does this code unit (byte) encode a code point by itself (US-ASCII 0..0x7f)?
162  * @param c 8-bit code unit (byte)
163  * @return TRUE or FALSE
164  * @stable ICU 2.4
165  */
166 #define U8_IS_SINGLE(c) (((c)&0x80)==0)
167 
168 /**
169  * Is this code unit (byte) a UTF-8 lead byte?
170  * @param c 8-bit code unit (byte)
171  * @return TRUE or FALSE
172  * @stable ICU 2.4
173  */
174 #define U8_IS_LEAD(c) ((uint8_t)((c)-0xc0)<0x3e)
175 
176 /**
177  * Is this code unit (byte) a UTF-8 trail byte?
178  * @param c 8-bit code unit (byte)
179  * @return TRUE or FALSE
180  * @stable ICU 2.4
181  */
182 #define U8_IS_TRAIL(c) (((c)&0xc0)==0x80)
183 
184 /**
185  * How many code units (bytes) are used for the UTF-8 encoding
186  * of this Unicode code point?
187  * @param c 32-bit code point
188  * @return 1..4, or 0 if c is a surrogate or not a Unicode code point
189  * @stable ICU 2.4
190  */
191 #define U8_LENGTH(c) \
192     ((uint32_t)(c)<=0x7f ? 1 : \
193         ((uint32_t)(c)<=0x7ff ? 2 : \
194             ((uint32_t)(c)<=0xd7ff ? 3 : \
195                 ((uint32_t)(c)<=0xdfff || (uint32_t)(c)>0x10ffff ? 0 : \
196                     ((uint32_t)(c)<=0xffff ? 3 : 4)\
197                 ) \
198             ) \
199         ) \
200     )
201 
202 /**
203  * The maximum number of UTF-8 code units (bytes) per Unicode code point (U+0000..U+10ffff).
204  * @return 4
205  * @stable ICU 2.4
206  */
207 #define U8_MAX_LENGTH 4
208 
209 /**
210  * Get a code point from a string at a random-access offset,
211  * without changing the offset.
212  * The offset may point to either the lead byte or one of the trail bytes
213  * for a code point, in which case the macro will read all of the bytes
214  * for the code point.
215  * The result is undefined if the offset points to an illegal UTF-8
216  * byte sequence.
217  * Iteration through a string is more efficient with U8_NEXT_UNSAFE or U8_NEXT.
218  *
219  * @param s const uint8_t * string
220  * @param i string offset
221  * @param c output UChar32 variable
222  * @see U8_GET
223  * @stable ICU 2.4
224  */
225 #define U8_GET_UNSAFE(s, i, c) { \
226     int32_t _u8_get_unsafe_index=(int32_t)(i); \
227     U8_SET_CP_START_UNSAFE(s, _u8_get_unsafe_index); \
228     U8_NEXT_UNSAFE(s, _u8_get_unsafe_index, c); \
229 }
230 
231 /**
232  * Get a code point from a string at a random-access offset,
233  * without changing the offset.
234  * The offset may point to either the lead byte or one of the trail bytes
235  * for a code point, in which case the macro will read all of the bytes
236  * for the code point.
237  *
238  * The length can be negative for a NUL-terminated string.
239  *
240  * If the offset points to an illegal UTF-8 byte sequence, then
241  * c is set to a negative value.
242  * Iteration through a string is more efficient with U8_NEXT_UNSAFE or U8_NEXT.
243  *
244  * @param s const uint8_t * string
245  * @param start int32_t starting string offset
246  * @param i int32_t string offset, must be start<=i<length
247  * @param length int32_t string length
248  * @param c output UChar32 variable, set to <0 in case of an error
249  * @see U8_GET_UNSAFE
250  * @stable ICU 2.4
251  */
252 #define U8_GET(s, start, i, length, c) { \
253     int32_t _u8_get_index=(i); \
254     U8_SET_CP_START(s, start, _u8_get_index); \
255     U8_NEXT(s, _u8_get_index, length, c); \
256 }
257 
258 /**
259  * Get a code point from a string at a random-access offset,
260  * without changing the offset.
261  * The offset may point to either the lead byte or one of the trail bytes
262  * for a code point, in which case the macro will read all of the bytes
263  * for the code point.
264  *
265  * The length can be negative for a NUL-terminated string.
266  *
267  * If the offset points to an illegal UTF-8 byte sequence, then
268  * c is set to U+FFFD.
269  * Iteration through a string is more efficient with U8_NEXT_UNSAFE or U8_NEXT_OR_FFFD.
270  *
271  * This macro does not distinguish between a real U+FFFD in the text
272  * and U+FFFD returned for an ill-formed sequence.
273  * Use U8_GET() if that distinction is important.
274  *
275  * @param s const uint8_t * string
276  * @param start int32_t starting string offset
277  * @param i int32_t string offset, must be start<=i<length
278  * @param length int32_t string length
279  * @param c output UChar32 variable, set to U+FFFD in case of an error
280  * @see U8_GET
281  * @stable ICU 51
282  */
283 #define U8_GET_OR_FFFD(s, start, i, length, c) { \
284     int32_t _u8_get_index=(i); \
285     U8_SET_CP_START(s, start, _u8_get_index); \
286     U8_NEXT_OR_FFFD(s, _u8_get_index, length, c); \
287 }
288 
289 /* definitions with forward iteration --------------------------------------- */
290 
291 /**
292  * Get a code point from a string at a code point boundary offset,
293  * and advance the offset to the next code point boundary.
294  * (Post-incrementing forward iteration.)
295  * "Unsafe" macro, assumes well-formed UTF-8.
296  *
297  * The offset may point to the lead byte of a multi-byte sequence,
298  * in which case the macro will read the whole sequence.
299  * The result is undefined if the offset points to a trail byte
300  * or an illegal UTF-8 sequence.
301  *
302  * @param s const uint8_t * string
303  * @param i string offset
304  * @param c output UChar32 variable
305  * @see U8_NEXT
306  * @stable ICU 2.4
307  */
308 #define U8_NEXT_UNSAFE(s, i, c) { \
309     (c)=(uint8_t)(s)[(i)++]; \
310     if((c)>=0x80) { \
311         if((c)<0xe0) { \
312             (c)=(((c)&0x1f)<<6)|((s)[(i)++]&0x3f); \
313         } else if((c)<0xf0) { \
314             /* no need for (c&0xf) because the upper bits are truncated after <<12 in the cast to (UChar) */ \
315             (c)=(UChar)(((c)<<12)|(((s)[i]&0x3f)<<6)|((s)[(i)+1]&0x3f)); \
316             (i)+=2; \
317         } else { \
318             (c)=(((c)&7)<<18)|(((s)[i]&0x3f)<<12)|(((s)[(i)+1]&0x3f)<<6)|((s)[(i)+2]&0x3f); \
319             (i)+=3; \
320         } \
321     } \
322 }
323 
324 /**
325  * Get a code point from a string at a code point boundary offset,
326  * and advance the offset to the next code point boundary.
327  * (Post-incrementing forward iteration.)
328  * "Safe" macro, checks for illegal sequences and for string boundaries.
329  *
330  * The length can be negative for a NUL-terminated string.
331  *
332  * The offset may point to the lead byte of a multi-byte sequence,
333  * in which case the macro will read the whole sequence.
334  * If the offset points to a trail byte or an illegal UTF-8 sequence, then
335  * c is set to a negative value.
336  *
337  * @param s const uint8_t * string
338  * @param i int32_t string offset, must be i<length
339  * @param length int32_t string length
340  * @param c output UChar32 variable, set to <0 in case of an error
341  * @see U8_NEXT_UNSAFE
342  * @stable ICU 2.4
343  */
344 #define U8_NEXT(s, i, length, c) { \
345     (c)=(uint8_t)(s)[(i)++]; \
346     if((c)>=0x80) { \
347         uint8_t __t1, __t2; \
348         if( /* handle U+1000..U+CFFF inline */ \
349             (0xe0<(c) && (c)<=0xec) && \
350             (((i)+1)<(length) || (length)<0) && \
351             (__t1=(uint8_t)((s)[i]-0x80))<=0x3f && \
352             (__t2=(uint8_t)((s)[(i)+1]-0x80))<= 0x3f \
353         ) { \
354             /* no need for (c&0xf) because the upper bits are truncated after <<12 in the cast to (UChar) */ \
355             (c)=(UChar)(((c)<<12)|(__t1<<6)|__t2); \
356             (i)+=2; \
357         } else if( /* handle U+0080..U+07FF inline */ \
358             ((c)<0xe0 && (c)>=0xc2) && \
359             ((i)!=(length)) && \
360             (__t1=(uint8_t)((s)[i]-0x80))<=0x3f \
361         ) { \
362             (c)=(((c)&0x1f)<<6)|__t1; \
363             ++(i); \
364         } else { \
365             /* function call for "complicated" and error cases */ \
366             (c)=utf8_nextCharSafeBody((const uint8_t *)s, &(i), (length), c, -1); \
367         } \
368     } \
369 }
370 
371 /**
372  * Get a code point from a string at a code point boundary offset,
373  * and advance the offset to the next code point boundary.
374  * (Post-incrementing forward iteration.)
375  * "Safe" macro, checks for illegal sequences and for string boundaries.
376  *
377  * The length can be negative for a NUL-terminated string.
378  *
379  * The offset may point to the lead byte of a multi-byte sequence,
380  * in which case the macro will read the whole sequence.
381  * If the offset points to a trail byte or an illegal UTF-8 sequence, then
382  * c is set to U+FFFD.
383  *
384  * This macro does not distinguish between a real U+FFFD in the text
385  * and U+FFFD returned for an ill-formed sequence.
386  * Use U8_NEXT() if that distinction is important.
387  *
388  * @param s const uint8_t * string
389  * @param i int32_t string offset, must be i<length
390  * @param length int32_t string length
391  * @param c output UChar32 variable, set to U+FFFD in case of an error
392  * @see U8_NEXT
393  * @stable ICU 51
394  */
395 #define U8_NEXT_OR_FFFD(s, i, length, c) { \
396     (c)=(uint8_t)(s)[(i)++]; \
397     if((c)>=0x80) { \
398         uint8_t __t1, __t2; \
399         if( /* handle U+1000..U+CFFF inline */ \
400             (0xe0<(c) && (c)<=0xec) && \
401             (((i)+1)<(length) || (length)<0) && \
402             (__t1=(uint8_t)((s)[i]-0x80))<=0x3f && \
403             (__t2=(uint8_t)((s)[(i)+1]-0x80))<= 0x3f \
404         ) { \
405             /* no need for (c&0xf) because the upper bits are truncated after <<12 in the cast to (UChar) */ \
406             (c)=(UChar)(((c)<<12)|(__t1<<6)|__t2); \
407             (i)+=2; \
408         } else if( /* handle U+0080..U+07FF inline */ \
409             ((c)<0xe0 && (c)>=0xc2) && \
410             ((i)!=(length)) && \
411             (__t1=(uint8_t)((s)[i]-0x80))<=0x3f \
412         ) { \
413             (c)=(((c)&0x1f)<<6)|__t1; \
414             ++(i); \
415         } else { \
416             /* function call for "complicated" and error cases */ \
417             (c)=utf8_nextCharSafeBody((const uint8_t *)s, &(i), (length), c, -3); \
418         } \
419     } \
420 }
421 
422 /**
423  * Append a code point to a string, overwriting 1 to 4 bytes.
424  * The offset points to the current end of the string contents
425  * and is advanced (post-increment).
426  * "Unsafe" macro, assumes a valid code point and sufficient space in the string.
427  * Otherwise, the result is undefined.
428  *
429  * @param s const uint8_t * string buffer
430  * @param i string offset
431  * @param c code point to append
432  * @see U8_APPEND
433  * @stable ICU 2.4
434  */
435 #define U8_APPEND_UNSAFE(s, i, c) { \
436     if((uint32_t)(c)<=0x7f) { \
437         (s)[(i)++]=(uint8_t)(c); \
438     } else { \
439         if((uint32_t)(c)<=0x7ff) { \
440             (s)[(i)++]=(uint8_t)(((c)>>6)|0xc0); \
441         } else { \
442             if((uint32_t)(c)<=0xffff) { \
443                 (s)[(i)++]=(uint8_t)(((c)>>12)|0xe0); \
444             } else { \
445                 (s)[(i)++]=(uint8_t)(((c)>>18)|0xf0); \
446                 (s)[(i)++]=(uint8_t)((((c)>>12)&0x3f)|0x80); \
447             } \
448             (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80); \
449         } \
450         (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80); \
451     } \
452 }
453 
454 /**
455  * Append a code point to a string, overwriting 1 to 4 bytes.
456  * The offset points to the current end of the string contents
457  * and is advanced (post-increment).
458  * "Safe" macro, checks for a valid code point.
459  * If a non-ASCII code point is written, checks for sufficient space in the string.
460  * If the code point is not valid or trail bytes do not fit,
461  * then isError is set to TRUE.
462  *
463  * @param s const uint8_t * string buffer
464  * @param i int32_t string offset, must be i<capacity
465  * @param capacity int32_t size of the string buffer
466  * @param c UChar32 code point to append
467  * @param isError output UBool set to TRUE if an error occurs, otherwise not modified
468  * @see U8_APPEND_UNSAFE
469  * @stable ICU 2.4
470  */
471 #define U8_APPEND(s, i, capacity, c, isError) { \
472     if((uint32_t)(c)<=0x7f) { \
473         (s)[(i)++]=(uint8_t)(c); \
474     } else if((uint32_t)(c)<=0x7ff && (i)+1<(capacity)) { \
475         (s)[(i)++]=(uint8_t)(((c)>>6)|0xc0); \
476         (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80); \
477     } else if((uint32_t)(c)<=0xd7ff && (i)+2<(capacity)) { \
478         (s)[(i)++]=(uint8_t)(((c)>>12)|0xe0); \
479         (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80); \
480         (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80); \
481     } else { \
482         (i)=utf8_appendCharSafeBody(s, (i), (capacity), c, &(isError)); \
483     } \
484 }
485 
486 /**
487  * Advance the string offset from one code point boundary to the next.
488  * (Post-incrementing iteration.)
489  * "Unsafe" macro, assumes well-formed UTF-8.
490  *
491  * @param s const uint8_t * string
492  * @param i string offset
493  * @see U8_FWD_1
494  * @stable ICU 2.4
495  */
496 #define U8_FWD_1_UNSAFE(s, i) { \
497     (i)+=1+U8_COUNT_TRAIL_BYTES_UNSAFE((uint8_t)(s)[i]); \
498 }
499 
500 /**
501  * Advance the string offset from one code point boundary to the next.
502  * (Post-incrementing iteration.)
503  * "Safe" macro, checks for illegal sequences and for string boundaries.
504  *
505  * The length can be negative for a NUL-terminated string.
506  *
507  * @param s const uint8_t * string
508  * @param i int32_t string offset, must be i<length
509  * @param length int32_t string length
510  * @see U8_FWD_1_UNSAFE
511  * @stable ICU 2.4
512  */
513 #define U8_FWD_1(s, i, length) { \
514     uint8_t __b=(uint8_t)(s)[(i)++]; \
515     if(U8_IS_LEAD(__b)) { \
516         uint8_t __count=U8_COUNT_TRAIL_BYTES(__b); \
517         if((i)+__count>(length) && (length)>=0) { \
518             __count=(uint8_t)((length)-(i)); \
519         } \
520         while(__count>0 && U8_IS_TRAIL((s)[i])) { \
521             ++(i); \
522             --__count; \
523         } \
524     } \
525 }
526 
527 /**
528  * Advance the string offset from one code point boundary to the n-th next one,
529  * i.e., move forward by n code points.
530  * (Post-incrementing iteration.)
531  * "Unsafe" macro, assumes well-formed UTF-8.
532  *
533  * @param s const uint8_t * string
534  * @param i string offset
535  * @param n number of code points to skip
536  * @see U8_FWD_N
537  * @stable ICU 2.4
538  */
539 #define U8_FWD_N_UNSAFE(s, i, n) { \
540     int32_t __N=(n); \
541     while(__N>0) { \
542         U8_FWD_1_UNSAFE(s, i); \
543         --__N; \
544     } \
545 }
546 
547 /**
548  * Advance the string offset from one code point boundary to the n-th next one,
549  * i.e., move forward by n code points.
550  * (Post-incrementing iteration.)
551  * "Safe" macro, checks for illegal sequences and for string boundaries.
552  *
553  * The length can be negative for a NUL-terminated string.
554  *
555  * @param s const uint8_t * string
556  * @param i int32_t string offset, must be i<length
557  * @param length int32_t string length
558  * @param n number of code points to skip
559  * @see U8_FWD_N_UNSAFE
560  * @stable ICU 2.4
561  */
562 #define U8_FWD_N(s, i, length, n) { \
563     int32_t __N=(n); \
564     while(__N>0 && ((i)<(length) || ((length)<0 && (s)[i]!=0))) { \
565         U8_FWD_1(s, i, length); \
566         --__N; \
567     } \
568 }
569 
570 /**
571  * Adjust a random-access offset to a code point boundary
572  * at the start of a code point.
573  * If the offset points to a UTF-8 trail byte,
574  * then the offset is moved backward to the corresponding lead byte.
575  * Otherwise, it is not modified.
576  * "Unsafe" macro, assumes well-formed UTF-8.
577  *
578  * @param s const uint8_t * string
579  * @param i string offset
580  * @see U8_SET_CP_START
581  * @stable ICU 2.4
582  */
583 #define U8_SET_CP_START_UNSAFE(s, i) { \
584     while(U8_IS_TRAIL((s)[i])) { --(i); } \
585 }
586 
587 /**
588  * Adjust a random-access offset to a code point boundary
589  * at the start of a code point.
590  * If the offset points to a UTF-8 trail byte,
591  * then the offset is moved backward to the corresponding lead byte.
592  * Otherwise, it is not modified.
593  * "Safe" macro, checks for illegal sequences and for string boundaries.
594  *
595  * @param s const uint8_t * string
596  * @param start int32_t starting string offset (usually 0)
597  * @param i int32_t string offset, must be start<=i
598  * @see U8_SET_CP_START_UNSAFE
599  * @stable ICU 2.4
600  */
601 #define U8_SET_CP_START(s, start, i) { \
602     if(U8_IS_TRAIL((s)[(i)])) { \
603         (i)=utf8_back1SafeBody(s, start, (i)); \
604     } \
605 }
606 
607 /* definitions with backward iteration -------------------------------------- */
608 
609 /**
610  * Move the string offset from one code point boundary to the previous one
611  * and get the code point between them.
612  * (Pre-decrementing backward iteration.)
613  * "Unsafe" macro, assumes well-formed UTF-8.
614  *
615  * The input offset may be the same as the string length.
616  * If the offset is behind a multi-byte sequence, then the macro will read
617  * the whole sequence.
618  * If the offset is behind a lead byte, then that itself
619  * will be returned as the code point.
620  * The result is undefined if the offset is behind an illegal UTF-8 sequence.
621  *
622  * @param s const uint8_t * string
623  * @param i string offset
624  * @param c output UChar32 variable
625  * @see U8_PREV
626  * @stable ICU 2.4
627  */
628 #define U8_PREV_UNSAFE(s, i, c) { \
629     (c)=(uint8_t)(s)[--(i)]; \
630     if(U8_IS_TRAIL(c)) { \
631         uint8_t __b, __count=1, __shift=6; \
632 \
633         /* c is a trail byte */ \
634         (c)&=0x3f; \
635         for(;;) { \
636             __b=(uint8_t)(s)[--(i)]; \
637             if(__b>=0xc0) { \
638                 U8_MASK_LEAD_BYTE(__b, __count); \
639                 (c)|=(UChar32)__b<<__shift; \
640                 break; \
641             } else { \
642                 (c)|=(UChar32)(__b&0x3f)<<__shift; \
643                 ++__count; \
644                 __shift+=6; \
645             } \
646         } \
647     } \
648 }
649 
650 /**
651  * Move the string offset from one code point boundary to the previous one
652  * and get the code point between them.
653  * (Pre-decrementing backward iteration.)
654  * "Safe" macro, checks for illegal sequences and for string boundaries.
655  *
656  * The input offset may be the same as the string length.
657  * If the offset is behind a multi-byte sequence, then the macro will read
658  * the whole sequence.
659  * If the offset is behind a lead byte, then that itself
660  * will be returned as the code point.
661  * If the offset is behind an illegal UTF-8 sequence, then c is set to a negative value.
662  *
663  * @param s const uint8_t * string
664  * @param start int32_t starting string offset (usually 0)
665  * @param i int32_t string offset, must be start<i
666  * @param c output UChar32 variable, set to <0 in case of an error
667  * @see U8_PREV_UNSAFE
668  * @stable ICU 2.4
669  */
670 #define U8_PREV(s, start, i, c) { \
671     (c)=(uint8_t)(s)[--(i)]; \
672     if((c)>=0x80) { \
673         (c)=utf8_prevCharSafeBody((const uint8_t *)s, start, &(i), c, -1); \
674     } \
675 }
676 
677 /**
678  * Move the string offset from one code point boundary to the previous one
679  * and get the code point between them.
680  * (Pre-decrementing backward iteration.)
681  * "Safe" macro, checks for illegal sequences and for string boundaries.
682  *
683  * The input offset may be the same as the string length.
684  * If the offset is behind a multi-byte sequence, then the macro will read
685  * the whole sequence.
686  * If the offset is behind a lead byte, then that itself
687  * will be returned as the code point.
688  * If the offset is behind an illegal UTF-8 sequence, then c is set to U+FFFD.
689  *
690  * This macro does not distinguish between a real U+FFFD in the text
691  * and U+FFFD returned for an ill-formed sequence.
692  * Use U8_PREV() if that distinction is important.
693  *
694  * @param s const uint8_t * string
695  * @param start int32_t starting string offset (usually 0)
696  * @param i int32_t string offset, must be start<i
697  * @param c output UChar32 variable, set to U+FFFD in case of an error
698  * @see U8_PREV
699  * @stable ICU 51
700  */
701 #define U8_PREV_OR_FFFD(s, start, i, c) { \
702     (c)=(uint8_t)(s)[--(i)]; \
703     if((c)>=0x80) { \
704         (c)=utf8_prevCharSafeBody((const uint8_t *)s, start, &(i), c, -3); \
705     } \
706 }
707 
708 /**
709  * Move the string offset from one code point boundary to the previous one.
710  * (Pre-decrementing backward iteration.)
711  * The input offset may be the same as the string length.
712  * "Unsafe" macro, assumes well-formed UTF-8.
713  *
714  * @param s const uint8_t * string
715  * @param i string offset
716  * @see U8_BACK_1
717  * @stable ICU 2.4
718  */
719 #define U8_BACK_1_UNSAFE(s, i) { \
720     while(U8_IS_TRAIL((s)[--(i)])) {} \
721 }
722 
723 /**
724  * Move the string offset from one code point boundary to the previous one.
725  * (Pre-decrementing backward iteration.)
726  * The input offset may be the same as the string length.
727  * "Safe" macro, checks for illegal sequences and for string boundaries.
728  *
729  * @param s const uint8_t * string
730  * @param start int32_t starting string offset (usually 0)
731  * @param i int32_t string offset, must be start<i
732  * @see U8_BACK_1_UNSAFE
733  * @stable ICU 2.4
734  */
735 #define U8_BACK_1(s, start, i) { \
736     if(U8_IS_TRAIL((s)[--(i)])) { \
737         (i)=utf8_back1SafeBody(s, start, (i)); \
738     } \
739 }
740 
741 /**
742  * Move the string offset from one code point boundary to the n-th one before it,
743  * i.e., move backward by n code points.
744  * (Pre-decrementing backward iteration.)
745  * The input offset may be the same as the string length.
746  * "Unsafe" macro, assumes well-formed UTF-8.
747  *
748  * @param s const uint8_t * string
749  * @param i string offset
750  * @param n number of code points to skip
751  * @see U8_BACK_N
752  * @stable ICU 2.4
753  */
754 #define U8_BACK_N_UNSAFE(s, i, n) { \
755     int32_t __N=(n); \
756     while(__N>0) { \
757         U8_BACK_1_UNSAFE(s, i); \
758         --__N; \
759     } \
760 }
761 
762 /**
763  * Move the string offset from one code point boundary to the n-th one before it,
764  * i.e., move backward by n code points.
765  * (Pre-decrementing backward iteration.)
766  * The input offset may be the same as the string length.
767  * "Safe" macro, checks for illegal sequences and for string boundaries.
768  *
769  * @param s const uint8_t * string
770  * @param start int32_t index of the start of the string
771  * @param i int32_t string offset, must be start<i
772  * @param n number of code points to skip
773  * @see U8_BACK_N_UNSAFE
774  * @stable ICU 2.4
775  */
776 #define U8_BACK_N(s, start, i, n) { \
777     int32_t __N=(n); \
778     while(__N>0 && (i)>(start)) { \
779         U8_BACK_1(s, start, i); \
780         --__N; \
781     } \
782 }
783 
784 /**
785  * Adjust a random-access offset to a code point boundary after a code point.
786  * If the offset is behind a partial multi-byte sequence,
787  * then the offset is incremented to behind the whole sequence.
788  * Otherwise, it is not modified.
789  * The input offset may be the same as the string length.
790  * "Unsafe" macro, assumes well-formed UTF-8.
791  *
792  * @param s const uint8_t * string
793  * @param i string offset
794  * @see U8_SET_CP_LIMIT
795  * @stable ICU 2.4
796  */
797 #define U8_SET_CP_LIMIT_UNSAFE(s, i) { \
798     U8_BACK_1_UNSAFE(s, i); \
799     U8_FWD_1_UNSAFE(s, i); \
800 }
801 
802 /**
803  * Adjust a random-access offset to a code point boundary after a code point.
804  * If the offset is behind a partial multi-byte sequence,
805  * then the offset is incremented to behind the whole sequence.
806  * Otherwise, it is not modified.
807  * The input offset may be the same as the string length.
808  * "Safe" macro, checks for illegal sequences and for string boundaries.
809  *
810  * The length can be negative for a NUL-terminated string.
811  *
812  * @param s const uint8_t * string
813  * @param start int32_t starting string offset (usually 0)
814  * @param i int32_t string offset, must be start<=i<=length
815  * @param length int32_t string length
816  * @see U8_SET_CP_LIMIT_UNSAFE
817  * @stable ICU 2.4
818  */
819 #define U8_SET_CP_LIMIT(s, start, i, length) { \
820     if((start)<(i) && ((i)<(length) || (length)<0)) { \
821         U8_BACK_1(s, start, i); \
822         U8_FWD_1(s, i, length); \
823     } \
824 }
825 
826 #endif
827