icuSources/common/unicode/utf8.h

   1 /*
   2 *******************************************************************************
   3 *
   4 *   Copyright (C) 1999-2013, International Business Machines
   5 *   Corporation and others.  All Rights Reserved.
   6 *
   7 *******************************************************************************
   8 *   file name:  utf8.h
   9 *   encoding:   US-ASCII
  10 *   tab size:   8 (not used)
  11 *   indentation:4
  12 *
  13 *   created on: 1999sep13
  14 *   created by: Markus W. Scherer
  15 */
  16
  17 /**
  18  * \file
  19  * \brief C API: 8-bit Unicode handling macros
  20  *
  21  * This file defines macros to deal with 8-bit Unicode (UTF-8) code units (bytes) and strings.
  22  *
  23  * For more information see utf.h and the ICU User Guide Strings chapter
  24  * (http://userguide.icu-project.org/strings).
  25  *
  26  * <em>Usage:</em>
  27  * ICU coding guidelines for if() statements should be followed when using these macros.
  28  * Compound statements (curly braces {}) must be used  for if-else-while...
  29  * bodies and all macro statements should be terminated with semicolon.
  30  */
  31
  32 #ifndef __UTF8_H__
  33 #define __UTF8_H__
  34
  35 #include "unicode/umachine.h"
  36 #ifndef __UTF_H__
  37 #   include "unicode/utf.h"
  38 #endif
  39
  40 /* internal definitions ----------------------------------------------------- */
  41
  42 /**
  43  * \var utf8_countTrailBytes
  44  * Internal array with numbers of trail bytes for any given byte used in
  45  * lead byte position.
  46  *
  47  * This is internal since it is not meant to be called directly by external clients;
  48  * however it is called by public macros in this file and thus must remain stable,
  49  * and should not be hidden when other internal functions are hidden (otherwise
  50  * public macros would fail to compile).
  51  * @internal
  52  */
  53 #ifdef U_UTF8_IMPL
  54 U_EXPORT const uint8_t
  55 #elif defined(U_STATIC_IMPLEMENTATION) || defined(U_COMMON_IMPLEMENTATION)
  56 U_CFUNC const uint8_t
  57 #else
  58 U_CFUNC U_IMPORT const uint8_t /* U_IMPORT2? */ /*U_IMPORT*/
  59 #endif
  60 utf8_countTrailBytes[256];
  61
  62 /**
  63  * Counts the trail bytes for a UTF-8 lead byte.
  64  * Returns 0 for 0..0xbf as well as for 0xfe and 0xff.
  65  *
  66  * This is internal since it is not meant to be called directly by external clients;
  67  * however it is called by public macros in this file and thus must remain stable.
  68  *
  69  * Note: Beginning with ICU 50, the implementation uses a multi-condition expression
  70  * which was shown in 2012 (on x86-64) to compile to fast, branch-free code.
  71  * leadByte is evaluated multiple times.
  72  *
  73  * The pre-ICU 50 implementation used the exported array utf8_countTrailBytes:
  74  * #define U8_COUNT_TRAIL_BYTES(leadByte) (utf8_countTrailBytes[leadByte])
  75  * leadByte was evaluated exactly once.
  76  *
  77  * @param leadByte The first byte of a UTF-8 sequence. Must be 0..0xff.
  78  * @internal
  79  */
  80 #define U8_COUNT_TRAIL_BYTES(leadByte) \
  81     ((leadByte)<0xf0 ? \
  82         ((leadByte)>=0xc0)+((leadByte)>=0xe0) : \
  83         (leadByte)<0xfe ? 3+((leadByte)>=0xf8)+((leadByte)>=0xfc) : 0)
  84
  85 /**
  86  * Counts the trail bytes for a UTF-8 lead byte of a valid UTF-8 sequence.
  87  * The maximum supported lead byte is 0xf4 corresponding to U+10FFFF.
  88  * leadByte might be evaluated multiple times.
  89  *
  90  * This is internal since it is not meant to be called directly by external clients;
  91  * however it is called by public macros in this file and thus must remain stable.
  92  *
  93  * @param leadByte The first byte of a UTF-8 sequence. Must be 0..0xff.
  94  * @internal
  95  */
  96 #define U8_COUNT_TRAIL_BYTES_UNSAFE(leadByte) \
  97     (((leadByte)>=0xc0)+((leadByte)>=0xe0)+((leadByte)>=0xf0))
  98
  99 /**
 100  * Mask a UTF-8 lead byte, leave only the lower bits that form part of the code point value.
 101  *
 102  * This is internal since it is not meant to be called directly by external clients;
 103  * however it is called by public macros in this file and thus must remain stable.
 104  * @internal
 105  */
 106 #define U8_MASK_LEAD_BYTE(leadByte, countTrailBytes) ((leadByte)&=(1<<(6-(countTrailBytes)))-1)
 107
 108 /**
 109  * Function for handling "next code point" with error-checking.
 110  *
 111  * This is internal since it is not meant to be called directly by external clients;
 112  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
 113  * file and thus must remain stable, and should not be hidden when other internal
 114  * functions are hidden (otherwise public macros would fail to compile).
 115  * @internal
 116  */
 117 U_STABLE UChar32 U_EXPORT2
 118 utf8_nextCharSafeBody(const uint8_t *s, int32_t *pi, int32_t length, UChar32 c, UBool strict);
 119
 120 /**
 121  * Function for handling "append code point" with error-checking.
 122  *
 123  * This is internal since it is not meant to be called directly by external clients;
 124  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
 125  * file and thus must remain stable, and should not be hidden when other internal
 126  * functions are hidden (otherwise public macros would fail to compile).
 127  * @internal
 128  */
 129 U_STABLE int32_t U_EXPORT2
 130 utf8_appendCharSafeBody(uint8_t *s, int32_t i, int32_t length, UChar32 c, UBool *pIsError);
 131
 132 /**
 133  * Function for handling "previous code point" with error-checking.
 134  *
 135  * This is internal since it is not meant to be called directly by external clients;
 136  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
 137  * file and thus must remain stable, and should not be hidden when other internal
 138  * functions are hidden (otherwise public macros would fail to compile).
 139  * @internal
 140  */
 141 U_STABLE UChar32 U_EXPORT2
 142 utf8_prevCharSafeBody(const uint8_t *s, int32_t start, int32_t *pi, UChar32 c, UBool strict);
 143
 144 /**
 145  * Function for handling "skip backward one code point" with error-checking.
 146  *
 147  * This is internal since it is not meant to be called directly by external clients;
 148  * however it is U_STABLE (not U_INTERNAL) since it is called by public macros in this
 149  * file and thus must remain stable, and should not be hidden when other internal
 150  * functions are hidden (otherwise public macros would fail to compile).
 151  * @internal
 152  */
 153 U_STABLE int32_t U_EXPORT2
 154 utf8_back1SafeBody(const uint8_t *s, int32_t start, int32_t i);
 155
 156 /* single-code point definitions -------------------------------------------- */
 157
 158 /**
 159  * Does this code unit (byte) encode a code point by itself (US-ASCII 0..0x7f)?
 160  * @param c 8-bit code unit (byte)
 161  * @return TRUE or FALSE
 162  * @stable ICU 2.4
 163  */
 164 #define U8_IS_SINGLE(c) (((c)&0x80)==0)
 165
 166 /**
 167  * Is this code unit (byte) a UTF-8 lead byte?
 168  * @param c 8-bit code unit (byte)
 169  * @return TRUE or FALSE
 170  * @stable ICU 2.4
 171  */
 172 #define U8_IS_LEAD(c) ((uint8_t)((c)-0xc0)<0x3e)
 173
 174 /**
 175  * Is this code unit (byte) a UTF-8 trail byte?
 176  * @param c 8-bit code unit (byte)
 177  * @return TRUE or FALSE
 178  * @stable ICU 2.4
 179  */
 180 #define U8_IS_TRAIL(c) (((c)&0xc0)==0x80)
 181
 182 /**
 183  * How many code units (bytes) are used for the UTF-8 encoding
 184  * of this Unicode code point?
 185  * @param c 32-bit code point
 186  * @return 1..4, or 0 if c is a surrogate or not a Unicode code point
 187  * @stable ICU 2.4
 188  */
 189 #define U8_LENGTH(c) \
 190     ((uint32_t)(c)<=0x7f ? 1 : \
 191         ((uint32_t)(c)<=0x7ff ? 2 : \
 192             ((uint32_t)(c)<=0xd7ff ? 3 : \
 193                 ((uint32_t)(c)<=0xdfff || (uint32_t)(c)>0x10ffff ? 0 : \
 194                     ((uint32_t)(c)<=0xffff ? 3 : 4)\
 195                 ) \
 196             ) \
 197         ) \
 198     )
 199
 200 /**
 201  * The maximum number of UTF-8 code units (bytes) per Unicode code point (U+0000..U+10ffff).
 202  * @return 4
 203  * @stable ICU 2.4
 204  */
 205 #define U8_MAX_LENGTH 4
 206
 207 /**
 208  * Get a code point from a string at a random-access offset,
 209  * without changing the offset.
 210  * The offset may point to either the lead byte or one of the trail bytes
 211  * for a code point, in which case the macro will read all of the bytes
 212  * for the code point.
 213  * The result is undefined if the offset points to an illegal UTF-8
 214  * byte sequence.
 215  * Iteration through a string is more efficient with U8_NEXT_UNSAFE or U8_NEXT.
 216  *
 217  * @param s const uint8_t * string
 218  * @param i string offset
 219  * @param c output UChar32 variable
 220  * @see U8_GET
 221  * @stable ICU 2.4
 222  */
 223 #define U8_GET_UNSAFE(s, i, c) { \
 224     int32_t _u8_get_unsafe_index=(int32_t)(i); \
 225     U8_SET_CP_START_UNSAFE(s, _u8_get_unsafe_index); \
 226     U8_NEXT_UNSAFE(s, _u8_get_unsafe_index, c); \
 227 }
 228
 229 /**
 230  * Get a code point from a string at a random-access offset,
 231  * without changing the offset.
 232  * The offset may point to either the lead byte or one of the trail bytes
 233  * for a code point, in which case the macro will read all of the bytes
 234  * for the code point.
 235  *
 236  * The length can be negative for a NUL-terminated string.
 237  *
 238  * If the offset points to an illegal UTF-8 byte sequence, then
 239  * c is set to a negative value.
 240  * Iteration through a string is more efficient with U8_NEXT_UNSAFE or U8_NEXT.
 241  *
 242  * @param s const uint8_t * string
 243  * @param start int32_t starting string offset
 244  * @param i int32_t string offset, must be start<=i<length
 245  * @param length int32_t string length
 246  * @param c output UChar32 variable, set to <0 in case of an error
 247  * @see U8_GET_UNSAFE
 248  * @stable ICU 2.4
 249  */
 250 #define U8_GET(s, start, i, length, c) { \
 251     int32_t _u8_get_index=(i); \
 252     U8_SET_CP_START(s, start, _u8_get_index); \
 253     U8_NEXT(s, _u8_get_index, length, c); \
 254 }
 255
 256 #ifndef U_HIDE_DRAFT_API
 257 /**
 258  * Get a code point from a string at a random-access offset,
 259  * without changing the offset.
 260  * The offset may point to either the lead byte or one of the trail bytes
 261  * for a code point, in which case the macro will read all of the bytes
 262  * for the code point.
 263  *
 264  * The length can be negative for a NUL-terminated string.
 265  *
 266  * If the offset points to an illegal UTF-8 byte sequence, then
 267  * c is set to U+FFFD.
 268  * Iteration through a string is more efficient with U8_NEXT_UNSAFE or U8_NEXT_OR_FFFD.
 269  *
 270  * This macro does not distinguish between a real U+FFFD in the text
 271  * and U+FFFD returned for an ill-formed sequence.
 272  * Use U8_GET() if that distinction is important.
 273  *
 274  * @param s const uint8_t * string
 275  * @param start int32_t starting string offset
 276  * @param i int32_t string offset, must be start<=i<length
 277  * @param length int32_t string length
 278  * @param c output UChar32 variable, set to U+FFFD in case of an error
 279  * @see U8_GET
 280  * @draft ICU 51
 281  */
 282 #define U8_GET_OR_FFFD(s, start, i, length, c) { \
 283     int32_t _u8_get_index=(i); \
 284     U8_SET_CP_START(s, start, _u8_get_index); \
 285     U8_NEXT_OR_FFFD(s, _u8_get_index, length, c); \
 286 }
 287 #endif /* U_HIDE_DRAFT_API */
 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 #ifndef U_HIDE_DRAFT_API
 372 /**
 373  * Get a code point from a string at a code point boundary offset,
 374  * and advance the offset to the next code point boundary.
 375  * (Post-incrementing forward iteration.)
 376  * "Safe" macro, checks for illegal sequences and for string boundaries.
 377  *
 378  * The length can be negative for a NUL-terminated string.
 379  *
 380  * The offset may point to the lead byte of a multi-byte sequence,
 381  * in which case the macro will read the whole sequence.
 382  * If the offset points to a trail byte or an illegal UTF-8 sequence, then
 383  * c is set to U+FFFD.
 384  *
 385  * This macro does not distinguish between a real U+FFFD in the text
 386  * and U+FFFD returned for an ill-formed sequence.
 387  * Use U8_NEXT() if that distinction is important.
 388  *
 389  * @param s const uint8_t * string
 390  * @param i int32_t string offset, must be i<length
 391  * @param length int32_t string length
 392  * @param c output UChar32 variable, set to U+FFFD in case of an error
 393  * @see U8_NEXT
 394  * @draft ICU 51
 395  */
 396 #define U8_NEXT_OR_FFFD(s, i, length, c) { \
 397     (c)=(uint8_t)(s)[(i)++]; \
 398     if((c)>=0x80) { \
 399         uint8_t __t1, __t2; \
 400         if( /* handle U+1000..U+CFFF inline */ \
 401             (0xe0<(c) && (c)<=0xec) && \
 402             (((i)+1)<(length) || (length)<0) && \
 403             (__t1=(uint8_t)((s)[i]-0x80))<=0x3f && \
 404             (__t2=(uint8_t)((s)[(i)+1]-0x80))<= 0x3f \
 405         ) { \
 406             /* no need for (c&0xf) because the upper bits are truncated after <<12 in the cast to (UChar) */ \
 407             (c)=(UChar)(((c)<<12)|(__t1<<6)|__t2); \
 408             (i)+=2; \
 409         } else if( /* handle U+0080..U+07FF inline */ \
 410             ((c)<0xe0 && (c)>=0xc2) && \
 411             ((i)!=(length)) && \
 412             (__t1=(uint8_t)((s)[i]-0x80))<=0x3f \
 413         ) { \
 414             (c)=(((c)&0x1f)<<6)|__t1; \
 415             ++(i); \
 416         } else { \
 417             /* function call for "complicated" and error cases */ \
 418             (c)=utf8_nextCharSafeBody((const uint8_t *)s, &(i), (length), c, -3); \
 419         } \
 420     } \
 421 }
 422 #endif /* U_HIDE_DRAFT_API */
 423
 424 /**
 425  * Append a code point to a string, overwriting 1 to 4 bytes.
 426  * The offset points to the current end of the string contents
 427  * and is advanced (post-increment).
 428  * "Unsafe" macro, assumes a valid code point and sufficient space in the string.
 429  * Otherwise, the result is undefined.
 430  *
 431  * @param s const uint8_t * string buffer
 432  * @param i string offset
 433  * @param c code point to append
 434  * @see U8_APPEND
 435  * @stable ICU 2.4
 436  */
 437 #define U8_APPEND_UNSAFE(s, i, c) { \
 438     if((uint32_t)(c)<=0x7f) { \
 439         (s)[(i)++]=(uint8_t)(c); \
 440     } else { \
 441         if((uint32_t)(c)<=0x7ff) { \
 442             (s)[(i)++]=(uint8_t)(((c)>>6)|0xc0); \
 443         } else { \
 444             if((uint32_t)(c)<=0xffff) { \
 445                 (s)[(i)++]=(uint8_t)(((c)>>12)|0xe0); \
 446             } else { \
 447                 (s)[(i)++]=(uint8_t)(((c)>>18)|0xf0); \
 448                 (s)[(i)++]=(uint8_t)((((c)>>12)&0x3f)|0x80); \
 449             } \
 450             (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80); \
 451         } \
 452         (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80); \
 453     } \
 454 }
 455
 456 /**
 457  * Append a code point to a string, overwriting 1 to 4 bytes.
 458  * The offset points to the current end of the string contents
 459  * and is advanced (post-increment).
 460  * "Safe" macro, checks for a valid code point.
 461  * If a non-ASCII code point is written, checks for sufficient space in the string.
 462  * If the code point is not valid or trail bytes do not fit,
 463  * then isError is set to TRUE.
 464  *
 465  * @param s const uint8_t * string buffer
 466  * @param i int32_t string offset, must be i<capacity
 467  * @param capacity int32_t size of the string buffer
 468  * @param c UChar32 code point to append
 469  * @param isError output UBool set to TRUE if an error occurs, otherwise not modified
 470  * @see U8_APPEND_UNSAFE
 471  * @stable ICU 2.4
 472  */
 473 #define U8_APPEND(s, i, capacity, c, isError) { \
 474     if((uint32_t)(c)<=0x7f) { \
 475         (s)[(i)++]=(uint8_t)(c); \
 476     } else if((uint32_t)(c)<=0x7ff && (i)+1<(capacity)) { \
 477         (s)[(i)++]=(uint8_t)(((c)>>6)|0xc0); \
 478         (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80); \
 479     } else if((uint32_t)(c)<=0xd7ff && (i)+2<(capacity)) { \
 480         (s)[(i)++]=(uint8_t)(((c)>>12)|0xe0); \
 481         (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80); \
 482         (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80); \
 483     } else { \
 484         (i)=utf8_appendCharSafeBody(s, (i), (capacity), c, &(isError)); \
 485     } \
 486 }
 487
 488 /**
 489  * Advance the string offset from one code point boundary to the next.
 490  * (Post-incrementing iteration.)
 491  * "Unsafe" macro, assumes well-formed UTF-8.
 492  *
 493  * @param s const uint8_t * string
 494  * @param i string offset
 495  * @see U8_FWD_1
 496  * @stable ICU 2.4
 497  */
 498 #define U8_FWD_1_UNSAFE(s, i) { \
 499     (i)+=1+U8_COUNT_TRAIL_BYTES_UNSAFE((uint8_t)(s)[i]); \
 500 }
 501
 502 /**
 503  * Advance the string offset from one code point boundary to the next.
 504  * (Post-incrementing iteration.)
 505  * "Safe" macro, checks for illegal sequences and for string boundaries.
 506  *
 507  * The length can be negative for a NUL-terminated string.
 508  *
 509  * @param s const uint8_t * string
 510  * @param i int32_t string offset, must be i<length
 511  * @param length int32_t string length
 512  * @see U8_FWD_1_UNSAFE
 513  * @stable ICU 2.4
 514  */
 515 #define U8_FWD_1(s, i, length) { \
 516     uint8_t __b=(uint8_t)(s)[(i)++]; \
 517     if(U8_IS_LEAD(__b)) { \
 518         uint8_t __count=U8_COUNT_TRAIL_BYTES(__b); \
 519         if((i)+__count>(length) && (length)>=0) { \
 520             __count=(uint8_t)((length)-(i)); \
 521         } \
 522         while(__count>0 && U8_IS_TRAIL((s)[i])) { \
 523             ++(i); \
 524             --__count; \
 525         } \
 526     } \
 527 }
 528
 529 /**
 530  * Advance the string offset from one code point boundary to the n-th next one,
 531  * i.e., move forward by n code points.
 532  * (Post-incrementing iteration.)
 533  * "Unsafe" macro, assumes well-formed UTF-8.
 534  *
 535  * @param s const uint8_t * string
 536  * @param i string offset
 537  * @param n number of code points to skip
 538  * @see U8_FWD_N
 539  * @stable ICU 2.4
 540  */
 541 #define U8_FWD_N_UNSAFE(s, i, n) { \
 542     int32_t __N=(n); \
 543     while(__N>0) { \
 544         U8_FWD_1_UNSAFE(s, i); \
 545         --__N; \
 546     } \
 547 }
 548
 549 /**
 550  * Advance the string offset from one code point boundary to the n-th next one,
 551  * i.e., move forward by n code points.
 552  * (Post-incrementing iteration.)
 553  * "Safe" macro, checks for illegal sequences and for string boundaries.
 554  *
 555  * The length can be negative for a NUL-terminated string.
 556  *
 557  * @param s const uint8_t * string
 558  * @param i int32_t string offset, must be i<length
 559  * @param length int32_t string length
 560  * @param n number of code points to skip
 561  * @see U8_FWD_N_UNSAFE
 562  * @stable ICU 2.4
 563  */
 564 #define U8_FWD_N(s, i, length, n) { \
 565     int32_t __N=(n); \
 566     while(__N>0 && ((i)<(length) || ((length)<0 && (s)[i]!=0))) { \
 567         U8_FWD_1(s, i, length); \
 568         --__N; \
 569     } \
 570 }
 571
 572 /**
 573  * Adjust a random-access offset to a code point boundary
 574  * at the start of a code point.
 575  * If the offset points to a UTF-8 trail byte,
 576  * then the offset is moved backward to the corresponding lead byte.
 577  * Otherwise, it is not modified.
 578  * "Unsafe" macro, assumes well-formed UTF-8.
 579  *
 580  * @param s const uint8_t * string
 581  * @param i string offset
 582  * @see U8_SET_CP_START
 583  * @stable ICU 2.4
 584  */
 585 #define U8_SET_CP_START_UNSAFE(s, i) { \
 586     while(U8_IS_TRAIL((s)[i])) { --(i); } \
 587 }
 588
 589 /**
 590  * Adjust a random-access offset to a code point boundary
 591  * at the start of a code point.
 592  * If the offset points to a UTF-8 trail byte,
 593  * then the offset is moved backward to the corresponding lead byte.
 594  * Otherwise, it is not modified.
 595  * "Safe" macro, checks for illegal sequences and for string boundaries.
 596  *
 597  * @param s const uint8_t * string
 598  * @param start int32_t starting string offset (usually 0)
 599  * @param i int32_t string offset, must be start<=i
 600  * @see U8_SET_CP_START_UNSAFE
 601  * @stable ICU 2.4
 602  */
 603 #define U8_SET_CP_START(s, start, i) { \
 604     if(U8_IS_TRAIL((s)[(i)])) { \
 605         (i)=utf8_back1SafeBody(s, start, (i)); \
 606     } \
 607 }
 608
 609 /* definitions with backward iteration -------------------------------------- */
 610
 611 /**
 612  * Move the string offset from one code point boundary to the previous one
 613  * and get the code point between them.
 614  * (Pre-decrementing backward iteration.)
 615  * "Unsafe" macro, assumes well-formed UTF-8.
 616  *
 617  * The input offset may be the same as the string length.
 618  * If the offset is behind a multi-byte sequence, then the macro will read
 619  * the whole sequence.
 620  * If the offset is behind a lead byte, then that itself
 621  * will be returned as the code point.
 622  * The result is undefined if the offset is behind an illegal UTF-8 sequence.
 623  *
 624  * @param s const uint8_t * string
 625  * @param i string offset
 626  * @param c output UChar32 variable
 627  * @see U8_PREV
 628  * @stable ICU 2.4
 629  */
 630 #define U8_PREV_UNSAFE(s, i, c) { \
 631     (c)=(uint8_t)(s)[--(i)]; \
 632     if(U8_IS_TRAIL(c)) { \
 633         uint8_t __b, __count=1, __shift=6; \
 634 \
 635         /* c is a trail byte */ \
 636         (c)&=0x3f; \
 637         for(;;) { \
 638             __b=(uint8_t)(s)[--(i)]; \
 639             if(__b>=0xc0) { \
 640                 U8_MASK_LEAD_BYTE(__b, __count); \
 641                 (c)|=(UChar32)__b<<__shift; \
 642                 break; \
 643             } else { \
 644                 (c)|=(UChar32)(__b&0x3f)<<__shift; \
 645                 ++__count; \
 646                 __shift+=6; \
 647             } \
 648         } \
 649     } \
 650 }
 651
 652 /**
 653  * Move the string offset from one code point boundary to the previous one
 654  * and get the code point between them.
 655  * (Pre-decrementing backward iteration.)
 656  * "Safe" macro, checks for illegal sequences and for string boundaries.
 657  *
 658  * The input offset may be the same as the string length.
 659  * If the offset is behind a multi-byte sequence, then the macro will read
 660  * the whole sequence.
 661  * If the offset is behind a lead byte, then that itself
 662  * will be returned as the code point.
 663  * If the offset is behind an illegal UTF-8 sequence, then c is set to a negative value.
 664  *
 665  * @param s const uint8_t * string
 666  * @param start int32_t starting string offset (usually 0)
 667  * @param i int32_t string offset, must be start<i
 668  * @param c output UChar32 variable, set to <0 in case of an error
 669  * @see U8_PREV_UNSAFE
 670  * @stable ICU 2.4
 671  */
 672 #define U8_PREV(s, start, i, c) { \
 673     (c)=(uint8_t)(s)[--(i)]; \
 674     if((c)>=0x80) { \
 675         (c)=utf8_prevCharSafeBody((const uint8_t *)s, start, &(i), c, -1); \
 676     } \
 677 }
 678
 679 #ifndef U_HIDE_DRAFT_API
 680 /**
 681  * Move the string offset from one code point boundary to the previous one
 682  * and get the code point between them.
 683  * (Pre-decrementing backward iteration.)
 684  * "Safe" macro, checks for illegal sequences and for string boundaries.
 685  *
 686  * The input offset may be the same as the string length.
 687  * If the offset is behind a multi-byte sequence, then the macro will read
 688  * the whole sequence.
 689  * If the offset is behind a lead byte, then that itself
 690  * will be returned as the code point.
 691  * If the offset is behind an illegal UTF-8 sequence, then c is set to U+FFFD.
 692  *
 693  * This macro does not distinguish between a real U+FFFD in the text
 694  * and U+FFFD returned for an ill-formed sequence.
 695  * Use U8_PREV() if that distinction is important.
 696  *
 697  * @param s const uint8_t * string
 698  * @param start int32_t starting string offset (usually 0)
 699  * @param i int32_t string offset, must be start<i
 700  * @param c output UChar32 variable, set to U+FFFD in case of an error
 701  * @see U8_PREV
 702  * @draft ICU 51
 703  */
 704 #define U8_PREV_OR_FFFD(s, start, i, c) { \
 705     (c)=(uint8_t)(s)[--(i)]; \
 706     if((c)>=0x80) { \
 707         (c)=utf8_prevCharSafeBody((const uint8_t *)s, start, &(i), c, -3); \
 708     } \
 709 }
 710 #endif /* U_HIDE_DRAFT_API */
 711
 712 /**
 713  * Move the string offset from one code point boundary to the previous one.
 714  * (Pre-decrementing backward iteration.)
 715  * The input offset may be the same as the string length.
 716  * "Unsafe" macro, assumes well-formed UTF-8.
 717  *
 718  * @param s const uint8_t * string
 719  * @param i string offset
 720  * @see U8_BACK_1
 721  * @stable ICU 2.4
 722  */
 723 #define U8_BACK_1_UNSAFE(s, i) { \
 724     while(U8_IS_TRAIL((s)[--(i)])) {} \
 725 }
 726
 727 /**
 728  * Move the string offset from one code point boundary to the previous one.
 729  * (Pre-decrementing backward iteration.)
 730  * The input offset may be the same as the string length.
 731  * "Safe" macro, checks for illegal sequences and for string boundaries.
 732  *
 733  * @param s const uint8_t * string
 734  * @param start int32_t starting string offset (usually 0)
 735  * @param i int32_t string offset, must be start<i
 736  * @see U8_BACK_1_UNSAFE
 737  * @stable ICU 2.4
 738  */
 739 #define U8_BACK_1(s, start, i) { \
 740     if(U8_IS_TRAIL((s)[--(i)])) { \
 741         (i)=utf8_back1SafeBody(s, start, (i)); \
 742     } \
 743 }
 744
 745 /**
 746  * Move the string offset from one code point boundary to the n-th one before it,
 747  * i.e., move backward by n code points.
 748  * (Pre-decrementing backward iteration.)
 749  * The input offset may be the same as the string length.
 750  * "Unsafe" macro, assumes well-formed UTF-8.
 751  *
 752  * @param s const uint8_t * string
 753  * @param i string offset
 754  * @param n number of code points to skip
 755  * @see U8_BACK_N
 756  * @stable ICU 2.4
 757  */
 758 #define U8_BACK_N_UNSAFE(s, i, n) { \
 759     int32_t __N=(n); \
 760     while(__N>0) { \
 761         U8_BACK_1_UNSAFE(s, i); \
 762         --__N; \
 763     } \
 764 }
 765
 766 /**
 767  * Move the string offset from one code point boundary to the n-th one before it,
 768  * i.e., move backward by n code points.
 769  * (Pre-decrementing backward iteration.)
 770  * The input offset may be the same as the string length.
 771  * "Safe" macro, checks for illegal sequences and for string boundaries.
 772  *
 773  * @param s const uint8_t * string
 774  * @param start int32_t index of the start of the string
 775  * @param i int32_t string offset, must be start<i
 776  * @param n number of code points to skip
 777  * @see U8_BACK_N_UNSAFE
 778  * @stable ICU 2.4
 779  */
 780 #define U8_BACK_N(s, start, i, n) { \
 781     int32_t __N=(n); \
 782     while(__N>0 && (i)>(start)) { \
 783         U8_BACK_1(s, start, i); \
 784         --__N; \
 785     } \
 786 }
 787
 788 /**
 789  * Adjust a random-access offset to a code point boundary after a code point.
 790  * If the offset is behind a partial multi-byte sequence,
 791  * then the offset is incremented to behind the whole sequence.
 792  * Otherwise, it is not modified.
 793  * The input offset may be the same as the string length.
 794  * "Unsafe" macro, assumes well-formed UTF-8.
 795  *
 796  * @param s const uint8_t * string
 797  * @param i string offset
 798  * @see U8_SET_CP_LIMIT
 799  * @stable ICU 2.4
 800  */
 801 #define U8_SET_CP_LIMIT_UNSAFE(s, i) { \
 802     U8_BACK_1_UNSAFE(s, i); \
 803     U8_FWD_1_UNSAFE(s, i); \
 804 }
 805
 806 /**
 807  * Adjust a random-access offset to a code point boundary after a code point.
 808  * If the offset is behind a partial multi-byte sequence,
 809  * then the offset is incremented to behind the whole sequence.
 810  * Otherwise, it is not modified.
 811  * The input offset may be the same as the string length.
 812  * "Safe" macro, checks for illegal sequences and for string boundaries.
 813  *
 814  * The length can be negative for a NUL-terminated string.
 815  *
 816  * @param s const uint8_t * string
 817  * @param start int32_t starting string offset (usually 0)
 818  * @param i int32_t string offset, must be start<=i<=length
 819  * @param length int32_t string length
 820  * @see U8_SET_CP_LIMIT_UNSAFE
 821  * @stable ICU 2.4
 822  */
 823 #define U8_SET_CP_LIMIT(s, start, i, length) { \
 824     if((start)<(i) && ((i)<(length) || ((length)<0 && (s)[i]!=0))) { \
 825         U8_BACK_1(s, start, i); \
 826         U8_FWD_1(s, i, length); \
 827     } \
 828 }
 829
 830 #endif