1/* Iterating through multibyte strings: macros for multi-byte encodings.
2   Copyright (C) 2001, 2005 Free Software Foundation, Inc.
3
4   This program is free software; you can redistribute it and/or modify
5   it under the terms of the GNU General Public License as published by
6   the Free Software Foundation; either version 2, or (at your option)
7   any later version.
8
9   This program 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 General Public License for more details.
13
14   You should have received a copy of the GNU General Public License
15   along with this program; if not, write to the Free Software Foundation,
16   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
17
18/* Written by Bruno Haible <bruno@clisp.org>.  */
19
20/* The macros in this file implement forward iteration through a
21   multi-byte string, without knowing its length a-priori.
22
23   With these macros, an iteration loop that looks like
24
25      char *iter;
26      for (iter = buf; *iter != '\0'; iter++)
27        {
28          do_something (*iter);
29        }
30
31   becomes
32
33      mbui_iterator_t iter;
34      for (mbui_init (iter, buf); mbui_avail (iter); mbui_advance (iter))
35        {
36          do_something (mbui_cur_ptr (iter), mb_len (mbui_cur (iter)));
37        }
38
39   The benefit of these macros over plain use of mbrtowc is:
40   - Handling of invalid multibyte sequences is possible without
41     making the code more complicated, while still preserving the
42     invalid multibyte sequences.
43
44   Compared to mbiter.h, the macros here don't need to know the string's
45   length a-priori.  The downside is that at each step, the look-ahead
46   that guards against overrunning the terminating '\0' is more expensive.
47   The mbui_* macros are therefore suitable when there is a high probability
48   that only the first few multibyte characters need to be inspected.
49   Whereas the mbi_* macros are better if usually the iteration runs
50   through the entire string.
51
52   mbui_iterator_t
53     is a type usable for variable declarations.
54
55   mbui_init (iter, startptr)
56     initializes the iterator, starting at startptr.
57
58   mbui_avail (iter)
59     returns true if there are more multibyte chracters available before
60     the end of string is reached. In this case, mbui_cur (iter) is
61     initialized to the next multibyte chracter.
62
63   mbui_advance (iter)
64     advances the iterator by one multibyte character.
65
66   mbui_cur (iter)
67     returns the current multibyte character, of type mbchar_t.  All the
68     macros defined in mbchar.h can be used on it.
69
70   mbui_cur_ptr (iter)
71     return a pointer to the beginning of the current multibyte character.
72
73   mbui_reloc (iter, ptrdiff)
74     relocates iterator when the string is moved by ptrdiff bytes.
75
76   Here are the function prototypes of the macros.
77
78   extern void		mbui_init (mbui_iterator_t iter, const char *startptr);
79   extern bool		mbui_avail (mbui_iterator_t iter);
80   extern void		mbui_advance (mbui_iterator_t iter);
81   extern mbchar_t	mbui_cur (mbui_iterator_t iter);
82   extern const char *	mbui_cur_ptr (mbui_iterator_t iter);
83   extern void		mbui_reloc (mbui_iterator_t iter, ptrdiff_t ptrdiff);
84 */
85
86#ifndef _MBUITER_H
87#define _MBUITER_H 1
88
89#include <assert.h>
90#include <stdbool.h>
91#include <stdlib.h>
92
93/* Tru64 with Desktop Toolkit C has a bug: <stdio.h> must be included before
94   <wchar.h>.
95   BSD/OS 4.1 has a bug: <stdio.h> and <time.h> must be included before
96   <wchar.h>.  */
97#include <stdio.h>
98#include <time.h>
99#include <wchar.h>
100
101#include "mbchar.h"
102#include "strnlen1.h"
103
104struct mbuiter_multi
105{
106  bool in_shift;	/* true if next byte may not be interpreted as ASCII */
107  mbstate_t state;	/* if in_shift: current shift state */
108  bool next_done;	/* true if mbui_avail has already filled the following */
109  struct mbchar cur;	/* the current character:
110	const char *cur.ptr		pointer to current character
111	The following are only valid after mbui_avail.
112	size_t cur.bytes		number of bytes of current character
113	bool cur.wc_valid		true if wc is a valid wide character
114	wchar_t cur.wc			if wc_valid: the current character
115	*/
116};
117
118static inline void
119mbuiter_multi_next (struct mbuiter_multi *iter)
120{
121  if (iter->next_done)
122    return;
123  if (iter->in_shift)
124    goto with_shift;
125  /* Handle most ASCII characters quickly, without calling mbrtowc().  */
126  if (is_basic (*iter->cur.ptr))
127    {
128      /* These characters are part of the basic character set.  ISO C 99
129	 guarantees that their wide character code is identical to their
130	 char code.  */
131      iter->cur.bytes = 1;
132      iter->cur.wc = *iter->cur.ptr;
133      iter->cur.wc_valid = true;
134    }
135  else
136    {
137      assert (mbsinit (&iter->state));
138      iter->in_shift = true;
139    with_shift:
140      iter->cur.bytes = mbrtowc (&iter->cur.wc, iter->cur.ptr,
141				 strnlen1 (iter->cur.ptr, MB_CUR_MAX),
142				 &iter->state);
143      if (iter->cur.bytes == (size_t) -1)
144	{
145	  /* An invalid multibyte sequence was encountered.  */
146	  iter->cur.bytes = 1;
147	  iter->cur.wc_valid = false;
148	  /* Whether to set iter->in_shift = false and reset iter->state
149	     or not is not very important; the string is bogus anyway.  */
150	}
151      else if (iter->cur.bytes == (size_t) -2)
152	{
153	  /* An incomplete multibyte character at the end.  */
154	  iter->cur.bytes = strlen (iter->cur.ptr);
155	  iter->cur.wc_valid = false;
156	  /* Whether to set iter->in_shift = false and reset iter->state
157	     or not is not important; the string end is reached anyway.  */
158	}
159      else
160	{
161	  if (iter->cur.bytes == 0)
162	    {
163	      /* A null wide character was encountered.  */
164	      iter->cur.bytes = 1;
165	      assert (*iter->cur.ptr == '\0');
166	      assert (iter->cur.wc == 0);
167	    }
168	  iter->cur.wc_valid = true;
169
170	  /* When in the initial state, we can go back treating ASCII
171	     characters more quickly.  */
172	  if (mbsinit (&iter->state))
173	    iter->in_shift = false;
174	}
175    }
176  iter->next_done = true;
177}
178
179static inline void
180mbuiter_multi_reloc (struct mbuiter_multi *iter, ptrdiff_t ptrdiff)
181{
182  iter->cur.ptr += ptrdiff;
183}
184
185/* Iteration macros.  */
186typedef struct mbuiter_multi mbui_iterator_t;
187#define mbui_init(iter, startptr) \
188  ((iter).cur.ptr = (startptr), \
189   (iter).in_shift = false, memset (&(iter).state, '\0', sizeof (mbstate_t)), \
190   (iter).next_done = false)
191#define mbui_avail(iter) \
192  (mbuiter_multi_next (&(iter)), !mb_isnul ((iter).cur))
193#define mbui_advance(iter) \
194  ((iter).cur.ptr += (iter).cur.bytes, (iter).next_done = false)
195
196/* Access to the current character.  */
197#define mbui_cur(iter) (iter).cur
198#define mbui_cur_ptr(iter) (iter).cur.ptr
199
200/* Relocation.  */
201#define mbui_reloc(iter, ptrdiff) mbuiter_multi_reloc (&iter, ptrdiff)
202
203#endif /* _MBUITER_H */
204