path: root/lib/mbiter.h

/* Iterating through multibyte strings: macros for multi-byte encodings.
   Copyright (C) 2001, 2005, 2007, 2009-2024 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* Written by Bruno Haible <bruno@clisp.org>.  */

/* The macros in this file implement forward iteration through a
   multi-byte string.

   With these macros, an iteration loop that looks like

      char *iter;
      for (iter = buf; iter < buf + buflen; iter++)
        {
          do_something (*iter);
        }

   becomes

      mbi_iterator_t iter;
      for (mbi_init (iter, buf, buflen); mbi_avail (iter); mbi_advance (iter))
        {
          do_something (mbi_cur_ptr (iter), mb_len (mbi_cur (iter)));
        }

   The benefit of these macros over plain use of mbrtowc is:
   - Handling of invalid multibyte sequences is possible without
     making the code more complicated, while still preserving the
     invalid multibyte sequences.

   mbi_iterator_t
     is a type usable for variable declarations.

   mbi_init (iter, startptr, length)
     initializes the iterator, starting at startptr and crossing length bytes.

   mbi_avail (iter)
     returns true if there are more multibyte characters available before
     the end of string is reached. In this case, mbi_cur (iter) is
     initialized to the next multibyte character.

   mbi_advance (iter)
     advances the iterator by one multibyte character.

   mbi_cur (iter)
     returns the current multibyte character, of type mbchar_t.  All the
     macros defined in mbchar.h can be used on it.

   mbi_cur_ptr (iter)
     return a pointer to the beginning of the current multibyte character.

   mbi_reloc (iter, ptrdiff)
     relocates iterator when the string is moved by ptrdiff bytes.

   mbi_copy (&destiter, &srciter)
     copies srciter to destiter.

   Here are the function prototypes of the macros.

   extern void          mbi_init (mbi_iterator_t iter,
                                  const char *startptr, size_t length);
   extern bool          mbi_avail (mbi_iterator_t iter);
   extern void          mbi_advance (mbi_iterator_t iter);
   extern mbchar_t      mbi_cur (mbi_iterator_t iter);
   extern const char *  mbi_cur_ptr (mbi_iterator_t iter);
   extern void          mbi_reloc (mbi_iterator_t iter, ptrdiff_t ptrdiff);
   extern void          mbi_copy (mbi_iterator_t *new, const mbi_iterator_t *old);
 */

#ifndef _MBITER_H
#define _MBITER_H 1

/* This file uses _GL_INLINE_HEADER_BEGIN, _GL_INLINE,
   _GL_ATTRIBUTE_ALWAYS_INLINE.  */
#if !_GL_CONFIG_H_INCLUDED
 #error "Please include config.h first."
#endif

#include <assert.h>
#include <stddef.h>
#include <string.h>
#include <uchar.h>
#include <wchar.h>

#include "mbchar.h"

_GL_INLINE_HEADER_BEGIN
#ifndef MBITER_INLINE
# define MBITER_INLINE _GL_INLINE _GL_ATTRIBUTE_ALWAYS_INLINE
#endif

struct mbiter_multi
{
  const char *limit;    /* pointer to end of string */
  #if !GNULIB_MBRTOC32_REGULAR
  bool in_shift;        /* true if next byte may not be interpreted as ASCII */
                        /* If GNULIB_MBRTOC32_REGULAR, it is always false,
                           so optimize it away.  */
  #endif
  mbstate_t state;      /* if in_shift: current shift state */
                        /* If GNULIB_MBRTOC32_REGULAR, it is in an initial state
                           before and after every mbiter_multi_next invocation.
                         */
  bool next_done;       /* true if mbi_avail has already filled the following */
  struct mbchar cur;    /* the current character:
        const char *cur.ptr          pointer to current character
        The following are only valid after mbi_avail.
        size_t cur.bytes             number of bytes of current character
        bool cur.wc_valid            true if wc is a valid 32-bit wide character
        char32_t cur.wc              if wc_valid: the current character
        */
};

MBITER_INLINE void
mbiter_multi_next (struct mbiter_multi *iter)
{
  if (iter->next_done)
    return;
  #if !GNULIB_MBRTOC32_REGULAR
  if (iter->in_shift)
    goto with_shift;
  #endif
  /* Handle most ASCII characters quickly, without calling mbrtowc().  */
  if (is_basic (*iter->cur.ptr))
    {
      /* These characters are part of the POSIX portable character set.
         For most of them, namely those in the ISO C basic character set,
         ISO C 99 guarantees that their wide character code is identical to
         their char code.  For the few other ones, this is the case as well,
         in all locale encodings that are in use.  The 32-bit wide character
         code is the same as well.  */
      iter->cur.bytes = 1;
      iter->cur.wc = *iter->cur.ptr;
      iter->cur.wc_valid = true;
    }
  else
    {
      assert (mbsinit (&iter->state));
      #if !GNULIB_MBRTOC32_REGULAR
      iter->in_shift = true;
    with_shift:
      #endif
      iter->cur.bytes = mbrtoc32 (&iter->cur.wc, iter->cur.ptr,
                                  iter->limit - iter->cur.ptr, &iter->state);
      if (iter->cur.bytes == (size_t) -1)
        {
          /* An invalid multibyte sequence was encountered.  */
          iter->cur.bytes = 1;
          iter->cur.wc_valid = false;
          /* Allow the next invocation to continue from a sane state.  */
          #if !GNULIB_MBRTOC32_REGULAR
          iter->in_shift = false;
          #endif
          mbszero (&iter->state);
        }
      else if (iter->cur.bytes == (size_t) -2)
        {
          /* An incomplete multibyte character at the end.  */
          iter->cur.bytes = iter->limit - iter->cur.ptr;
          iter->cur.wc_valid = false;
          #if !GNULIB_MBRTOC32_REGULAR
          /* Cause the next mbi_avail invocation to return false.  */
          iter->in_shift = false;
          #endif
          /* Whether to reset iter->state or not is not important; the
             string end is reached anyway.  */
        }
      else
        {
          if (iter->cur.bytes == 0)
            {
              /* A null wide character was encountered.  */
              iter->cur.bytes = 1;
              assert (*iter->cur.ptr == '\0');
              assert (iter->cur.wc == 0);
            }
          #if !GNULIB_MBRTOC32_REGULAR
          else if (iter->cur.bytes == (size_t) -3)
            /* The previous multibyte sequence produced an additional 32-bit
               wide character.  */
            iter->cur.bytes = 0;
          #endif
          iter->cur.wc_valid = true;

          /* When in an initial state, we can go back treating ASCII
             characters more quickly.  */
          #if !GNULIB_MBRTOC32_REGULAR
          if (mbsinit (&iter->state))
            iter->in_shift = false;
          #endif
        }
    }
  iter->next_done = true;
}

MBITER_INLINE void
mbiter_multi_reloc (struct mbiter_multi *iter, ptrdiff_t ptrdiff)
{
  iter->cur.ptr += ptrdiff;
  iter->limit += ptrdiff;
}

MBITER_INLINE void
mbiter_multi_copy (struct mbiter_multi *new_iter, const struct mbiter_multi *old_iter)
{
  new_iter->limit = old_iter->limit;
  #if !GNULIB_MBRTOC32_REGULAR
  if ((new_iter->in_shift = old_iter->in_shift))
    memcpy (&new_iter->state, &old_iter->state, sizeof (mbstate_t));
  else
  #endif
    mbszero (&new_iter->state);
  new_iter->next_done = old_iter->next_done;
  mb_copy (&new_iter->cur, &old_iter->cur);
}

/* Iteration macros.  */
typedef struct mbiter_multi mbi_iterator_t;
#if !GNULIB_MBRTOC32_REGULAR
#define mbi_init(iter, startptr, length) \
  ((iter).cur.ptr = (startptr), (iter).limit = (iter).cur.ptr + (length), \
   (iter).in_shift = false, mbszero (&(iter).state), \
   (iter).next_done = false)
#else
/* Optimized: no in_shift.  */
#define mbi_init(iter, startptr, length) \
  ((iter).cur.ptr = (startptr), (iter).limit = (iter).cur.ptr + (length), \
   mbszero (&(iter).state), \
   (iter).next_done = false)
#endif
#if !GNULIB_MBRTOC32_REGULAR
#define mbi_avail(iter) \
  (((iter).cur.ptr < (iter).limit || (iter).in_shift) \
   && (mbiter_multi_next (&(iter)), true))
#else
/* Optimized: no in_shift.  */
#define mbi_avail(iter) \
  ((iter).cur.ptr < (iter).limit \
   && (mbiter_multi_next (&(iter)), true))
#endif
#define mbi_advance(iter) \
  ((iter).cur.ptr += (iter).cur.bytes, (iter).next_done = false)

/* Access to the current character.  */
#define mbi_cur(iter) (iter).cur
#define mbi_cur_ptr(iter) (iter).cur.ptr

/* Relocation.  */
#define mbi_reloc(iter, ptrdiff) mbiter_multi_reloc (&iter, ptrdiff)

/* Copying an iterator.  */
#define mbi_copy mbiter_multi_copy

_GL_INLINE_HEADER_END

#endif /* _MBITER_H */