lib/mbiter.h

   1 /* Iterating through multibyte strings: macros for multi-byte encodings.
   2    Copyright (C) 2001, 2005, 2007, 2009-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>.  */
  18
  19 /* The macros in this file implement forward iteration through a
  20    multi-byte string.
  21
  22    With these macros, an iteration loop that looks like
  23
  24       char *iter;
  25       for (iter = buf; iter < buf + buflen; iter++)
  26         {
  27           do_something (*iter);
  28         }
  29
  30    becomes
  31
  32       mbi_iterator_t iter;
  33       for (mbi_init (iter, buf, buflen); mbi_avail (iter); mbi_advance (iter))
  34         {
  35           do_something (mbi_cur_ptr (iter), mb_len (mbi_cur (iter)));
  36         }
  37
  38    The benefit of these macros over plain use of mbrtowc is:
  39    - Handling of invalid multibyte sequences is possible without
  40      making the code more complicated, while still preserving the
  41      invalid multibyte sequences.
  42
  43    mbi_iterator_t
  44      is a type usable for variable declarations.
  45
  46    mbi_init (iter, startptr, length)
  47      initializes the iterator, starting at startptr and crossing length bytes.
  48
  49    mbi_avail (iter)
  50      returns true if there are more multibyte characters available before
  51      the end of string is reached. In this case, mbi_cur (iter) is
  52      initialized to the next multibyte character.
  53
  54    mbi_advance (iter)
  55      advances the iterator by one multibyte character.
  56
  57    mbi_cur (iter)
  58      returns the current multibyte character, of type mbchar_t.  All the
  59      macros defined in mbchar.h can be used on it.
  60
  61    mbi_cur_ptr (iter)
  62      return a pointer to the beginning of the current multibyte character.
  63
  64    mbi_reloc (iter, ptrdiff)
  65      relocates iterator when the string is moved by ptrdiff bytes.
  66
  67    mbi_copy (&destiter, &srciter)
  68      copies srciter to destiter.
  69
  70    Here are the function prototypes of the macros.
  71
  72    extern void          mbi_init (mbi_iterator_t iter,
  73                                   const char *startptr, size_t length);
  74    extern bool          mbi_avail (mbi_iterator_t iter);
  75    extern void          mbi_advance (mbi_iterator_t iter);
  76    extern mbchar_t      mbi_cur (mbi_iterator_t iter);
  77    extern const char *  mbi_cur_ptr (mbi_iterator_t iter);
  78    extern void          mbi_reloc (mbi_iterator_t iter, ptrdiff_t ptrdiff);
  79    extern void          mbi_copy (mbi_iterator_t *new, const mbi_iterator_t *old);
  80  */
  81
  82 #ifndef _MBITER_H
  83 #define _MBITER_H 1
  84
  85 /* This file uses _GL_INLINE_HEADER_BEGIN, _GL_INLINE,
  86    _GL_ATTRIBUTE_ALWAYS_INLINE.  */
  87 #if !_GL_CONFIG_H_INCLUDED
  88  #error "Please include config.h first."
  89 #endif
  90
  91 #include <assert.h>
  92 #include <stddef.h>
  93 #include <string.h>
  94 #include <uchar.h>
  95 #include <wchar.h>
  96
  97 #include "mbchar.h"
  98
  99 _GL_INLINE_HEADER_BEGIN
 100 #ifndef MBITER_INLINE
 101 # define MBITER_INLINE _GL_INLINE _GL_ATTRIBUTE_ALWAYS_INLINE
 102 #endif
 103
 104 struct mbiter_multi
 105 {
 106   const char *limit;    /* pointer to end of string */
 107   #if !GNULIB_MBRTOC32_REGULAR
 108   bool in_shift;        /* true if next byte may not be interpreted as ASCII */
 109                         /* If GNULIB_MBRTOC32_REGULAR, it is always false,
 110                            so optimize it away.  */
 111   #endif
 112   mbstate_t state;      /* if in_shift: current shift state */
 113                         /* If GNULIB_MBRTOC32_REGULAR, it is in an initial state
 114                            before and after every mbiter_multi_next invocation.
 115                          */
 116   bool next_done;       /* true if mbi_avail has already filled the following */
 117   struct mbchar cur;    /* the current character:
 118         const char *cur.ptr          pointer to current character
 119         The following are only valid after mbi_avail.
 120         size_t cur.bytes             number of bytes of current character
 121         bool cur.wc_valid            true if wc is a valid 32-bit wide character
 122         char32_t cur.wc              if wc_valid: the current character
 123         */
 124 };
 125
 126 MBITER_INLINE void
 127 mbiter_multi_next (struct mbiter_multi *iter)
 128 {
 129   if (iter->next_done)
 130     return;
 131   #if !GNULIB_MBRTOC32_REGULAR
 132   if (iter->in_shift)
 133     goto with_shift;
 134   #endif
 135   /* Handle most ASCII characters quickly, without calling mbrtowc().  */
 136   if (is_basic (*iter->cur.ptr))
 137     {
 138       /* These characters are part of the POSIX portable character set.
 139          For most of them, namely those in the ISO C basic character set,
 140          ISO C 99 guarantees that their wide character code is identical to
 141          their char code.  For the few other ones, this is the case as well,
 142          in all locale encodings that are in use.  The 32-bit wide character
 143          code is the same as well.  */
 144       iter->cur.bytes = 1;
 145       iter->cur.wc = *iter->cur.ptr;
 146       iter->cur.wc_valid = true;
 147     }
 148   else
 149     {
 150       assert (mbsinit (&iter->state));
 151       #if !GNULIB_MBRTOC32_REGULAR
 152       iter->in_shift = true;
 153     with_shift:
 154       #endif
 155       iter->cur.bytes = mbrtoc32 (&iter->cur.wc, iter->cur.ptr,
 156                                   iter->limit - iter->cur.ptr, &iter->state);
 157       if (iter->cur.bytes == (size_t) -1)
 158         {
 159           /* An invalid multibyte sequence was encountered.  */
 160           iter->cur.bytes = 1;
 161           iter->cur.wc_valid = false;
 162           /* Allow the next invocation to continue from a sane state.  */
 163           #if !GNULIB_MBRTOC32_REGULAR
 164           iter->in_shift = false;
 165           #endif
 166           mbszero (&iter->state);
 167         }
 168       else if (iter->cur.bytes == (size_t) -2)
 169         {
 170           /* An incomplete multibyte character at the end.  */
 171           iter->cur.bytes = iter->limit - iter->cur.ptr;
 172           iter->cur.wc_valid = false;
 173           #if !GNULIB_MBRTOC32_REGULAR
 174           /* Cause the next mbi_avail invocation to return false.  */
 175           iter->in_shift = false;
 176           #endif
 177           /* Whether to reset iter->state or not is not important; the
 178              string end is reached anyway.  */
 179         }
 180       else
 181         {
 182           if (iter->cur.bytes == 0)
 183             {
 184               /* A null wide character was encountered.  */
 185               iter->cur.bytes = 1;
 186               assert (*iter->cur.ptr == '\0');
 187               assert (iter->cur.wc == 0);
 188             }
 189           #if !GNULIB_MBRTOC32_REGULAR
 190           else if (iter->cur.bytes == (size_t) -3)
 191             /* The previous multibyte sequence produced an additional 32-bit
 192                wide character.  */
 193             iter->cur.bytes = 0;
 194           #endif
 195           iter->cur.wc_valid = true;
 196
 197           /* When in an initial state, we can go back treating ASCII
 198              characters more quickly.  */
 199           #if !GNULIB_MBRTOC32_REGULAR
 200           if (mbsinit (&iter->state))
 201             iter->in_shift = false;
 202           #endif
 203         }
 204     }
 205   iter->next_done = true;
 206 }
 207
 208 MBITER_INLINE void
 209 mbiter_multi_reloc (struct mbiter_multi *iter, ptrdiff_t ptrdiff)
 210 {
 211   iter->cur.ptr += ptrdiff;
 212   iter->limit += ptrdiff;
 213 }
 214
 215 MBITER_INLINE void
 216 mbiter_multi_copy (struct mbiter_multi *new_iter, const struct mbiter_multi *old_iter)
 217 {
 218   new_iter->limit = old_iter->limit;
 219   #if !GNULIB_MBRTOC32_REGULAR
 220   if ((new_iter->in_shift = old_iter->in_shift))
 221     memcpy (&new_iter->state, &old_iter->state, sizeof (mbstate_t));
 222   else
 223   #endif
 224     mbszero (&new_iter->state);
 225   new_iter->next_done = old_iter->next_done;
 226   mb_copy (&new_iter->cur, &old_iter->cur);
 227 }
 228
 229 /* Iteration macros.  */
 230 typedef struct mbiter_multi mbi_iterator_t;
 231 #if !GNULIB_MBRTOC32_REGULAR
 232 #define mbi_init(iter, startptr, length) \
 233   ((iter).cur.ptr = (startptr), (iter).limit = (iter).cur.ptr + (length), \
 234    (iter).in_shift = false, mbszero (&(iter).state), \
 235    (iter).next_done = false)
 236 #else
 237 /* Optimized: no in_shift.  */
 238 #define mbi_init(iter, startptr, length) \
 239   ((iter).cur.ptr = (startptr), (iter).limit = (iter).cur.ptr + (length), \
 240    mbszero (&(iter).state), \
 241    (iter).next_done = false)
 242 #endif
 243 #if !GNULIB_MBRTOC32_REGULAR
 244 #define mbi_avail(iter) \
 245   (((iter).cur.ptr < (iter).limit || (iter).in_shift) \
 246    && (mbiter_multi_next (&(iter)), true))
 247 #else
 248 /* Optimized: no in_shift.  */
 249 #define mbi_avail(iter) \
 250   ((iter).cur.ptr < (iter).limit \
 251    && (mbiter_multi_next (&(iter)), true))
 252 #endif
 253 #define mbi_advance(iter) \
 254   ((iter).cur.ptr += (iter).cur.bytes, (iter).next_done = false)
 255
 256 /* Access to the current character.  */
 257 #define mbi_cur(iter) (iter).cur
 258 #define mbi_cur_ptr(iter) (iter).cur.ptr
 259
 260 /* Relocation.  */
 261 #define mbi_reloc(iter, ptrdiff) mbiter_multi_reloc (&iter, ptrdiff)
 262
 263 /* Copying an iterator.  */
 264 #define mbi_copy mbiter_multi_copy
 265
 266 _GL_INLINE_HEADER_END
 267
 268 #endif /* _MBITER_H */