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  • only in /netgear-WNDR4500v2-V1.0.0.60_1.0.38/ap/gpl/timemachine/gettext-0.17/gettext-runtime/gnulib-lib/
1/* Searching in a string.
2   Copyright (C) 2005-2007 Free Software Foundation, Inc.
3   Written by Bruno Haible <bruno@clisp.org>, 2005.
4
5   This program is free software: you can redistribute it and/or modify
6   it under the terms of the GNU General Public License as published by
7   the Free Software Foundation; either version 3 of the License, or
8   (at your option) any later version.
9
10   This program is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13   GNU General Public License for more details.
14
15   You should have received a copy of the GNU General Public License
16   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
17
18#include <config.h>
19
20/* Specification.  */
21#include <string.h>
22
23#include <stdbool.h>
24#include <stddef.h>  /* for NULL, in case a nonstandard string.h lacks it */
25
26#include "malloca.h"
27#if HAVE_MBRTOWC
28# include "mbuiter.h"
29#endif
30
31/* Knuth-Morris-Pratt algorithm.
32   See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
33   Return a boolean indicating success.  */
34
35static bool
36knuth_morris_pratt_unibyte (const char *haystack, const char *needle,
37			    const char **resultp)
38{
39  size_t m = strlen (needle);
40
41  /* Allocate the table.  */
42  size_t *table = (size_t *) malloca (m * sizeof (size_t));
43  if (table == NULL)
44    return false;
45  /* Fill the table.
46     For 0 < i < m:
47       0 < table[i] <= i is defined such that
48       rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i]
49       implies
50       forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1],
51       and table[i] is as large as possible with this property.
52     table[0] remains uninitialized.  */
53  {
54    size_t i, j;
55
56    table[1] = 1;
57    j = 0;
58    for (i = 2; i < m; i++)
59      {
60	unsigned char b = (unsigned char) needle[i - 1];
61
62	for (;;)
63	  {
64	    if (b == (unsigned char) needle[j])
65	      {
66		table[i] = i - ++j;
67		break;
68	      }
69	    if (j == 0)
70	      {
71		table[i] = i;
72		break;
73	      }
74	    j = j - table[j];
75	  }
76      }
77  }
78
79  /* Search, using the table to accelerate the processing.  */
80  {
81    size_t j;
82    const char *rhaystack;
83    const char *phaystack;
84
85    *resultp = NULL;
86    j = 0;
87    rhaystack = haystack;
88    phaystack = haystack;
89    /* Invariant: phaystack = rhaystack + j.  */
90    while (*phaystack != '\0')
91      if ((unsigned char) needle[j] == (unsigned char) *phaystack)
92	{
93	  j++;
94	  phaystack++;
95	  if (j == m)
96	    {
97	      /* The entire needle has been found.  */
98	      *resultp = rhaystack;
99	      break;
100	    }
101	}
102      else if (j > 0)
103	{
104	  /* Found a match of needle[0..j-1], mismatch at needle[j].  */
105	  rhaystack += table[j];
106	  j -= table[j];
107	}
108      else
109	{
110	  /* Found a mismatch at needle[0] already.  */
111	  rhaystack++;
112	  phaystack++;
113	}
114  }
115
116  freea (table);
117  return true;
118}
119
120#if HAVE_MBRTOWC
121static bool
122knuth_morris_pratt_multibyte (const char *haystack, const char *needle,
123			      const char **resultp)
124{
125  size_t m = mbslen (needle);
126  mbchar_t *needle_mbchars;
127  size_t *table;
128
129  /* Allocate room for needle_mbchars and the table.  */
130  char *memory = (char *) malloca (m * (sizeof (mbchar_t) + sizeof (size_t)));
131  if (memory == NULL)
132    return false;
133  needle_mbchars = (mbchar_t *) memory;
134  table = (size_t *) (memory + m * sizeof (mbchar_t));
135
136  /* Fill needle_mbchars.  */
137  {
138    mbui_iterator_t iter;
139    size_t j;
140
141    j = 0;
142    for (mbui_init (iter, needle); mbui_avail (iter); mbui_advance (iter), j++)
143      mb_copy (&needle_mbchars[j], &mbui_cur (iter));
144  }
145
146  /* Fill the table.
147     For 0 < i < m:
148       0 < table[i] <= i is defined such that
149       rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i]
150       implies
151       forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1],
152       and table[i] is as large as possible with this property.
153     table[0] remains uninitialized.  */
154  {
155    size_t i, j;
156
157    table[1] = 1;
158    j = 0;
159    for (i = 2; i < m; i++)
160      {
161	mbchar_t *b = &needle_mbchars[i - 1];
162
163	for (;;)
164	  {
165	    if (mb_equal (*b, needle_mbchars[j]))
166	      {
167		table[i] = i - ++j;
168		break;
169	      }
170	    if (j == 0)
171	      {
172		table[i] = i;
173		break;
174	      }
175	    j = j - table[j];
176	  }
177      }
178  }
179
180  /* Search, using the table to accelerate the processing.  */
181  {
182    size_t j;
183    mbui_iterator_t rhaystack;
184    mbui_iterator_t phaystack;
185
186    *resultp = NULL;
187    j = 0;
188    mbui_init (rhaystack, haystack);
189    mbui_init (phaystack, haystack);
190    /* Invariant: phaystack = rhaystack + j.  */
191    while (mbui_avail (phaystack))
192      if (mb_equal (needle_mbchars[j], mbui_cur (phaystack)))
193	{
194	  j++;
195	  mbui_advance (phaystack);
196	  if (j == m)
197	    {
198	      /* The entire needle has been found.  */
199	      *resultp = mbui_cur_ptr (rhaystack);
200	      break;
201	    }
202	}
203      else if (j > 0)
204	{
205	  /* Found a match of needle[0..j-1], mismatch at needle[j].  */
206	  size_t count = table[j];
207	  j -= count;
208	  for (; count > 0; count--)
209	    {
210	      if (!mbui_avail (rhaystack))
211		abort ();
212	      mbui_advance (rhaystack);
213	    }
214	}
215      else
216	{
217	  /* Found a mismatch at needle[0] already.  */
218	  if (!mbui_avail (rhaystack))
219	    abort ();
220	  mbui_advance (rhaystack);
221	  mbui_advance (phaystack);
222	}
223  }
224
225  freea (memory);
226  return true;
227}
228#endif
229
230/* Find the first occurrence of the character string NEEDLE in the character
231   string HAYSTACK.  Return NULL if NEEDLE is not found in HAYSTACK.  */
232char *
233mbsstr (const char *haystack, const char *needle)
234{
235  /* Be careful not to look at the entire extent of haystack or needle
236     until needed.  This is useful because of these two cases:
237       - haystack may be very long, and a match of needle found early,
238       - needle may be very long, and not even a short initial segment of
239         needle may be found in haystack.  */
240#if HAVE_MBRTOWC
241  if (MB_CUR_MAX > 1)
242    {
243      mbui_iterator_t iter_needle;
244
245      mbui_init (iter_needle, needle);
246      if (mbui_avail (iter_needle))
247	{
248	  /* Minimizing the worst-case complexity:
249	     Let n = mbslen(haystack), m = mbslen(needle).
250	     The na��ve algorithm is O(n*m) worst-case.
251	     The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
252	     memory allocation.
253	     To achieve linear complexity and yet amortize the cost of the
254	     memory allocation, we activate the Knuth-Morris-Pratt algorithm
255	     only once the na��ve algorithm has already run for some time; more
256	     precisely, when
257	       - the outer loop count is >= 10,
258	       - the average number of comparisons per outer loop is >= 5,
259	       - the total number of comparisons is >= m.
260	     But we try it only once.  If the memory allocation attempt failed,
261	     we don't retry it.  */
262	  bool try_kmp = true;
263	  size_t outer_loop_count = 0;
264	  size_t comparison_count = 0;
265	  size_t last_ccount = 0;		   /* last comparison count */
266	  mbui_iterator_t iter_needle_last_ccount; /* = needle + last_ccount */
267
268	  mbui_iterator_t iter_haystack;
269
270	  mbui_init (iter_needle_last_ccount, needle);
271	  mbui_init (iter_haystack, haystack);
272	  for (;; mbui_advance (iter_haystack))
273	    {
274	      if (!mbui_avail (iter_haystack))
275		/* No match.  */
276		return NULL;
277
278	      /* See whether it's advisable to use an asymptotically faster
279		 algorithm.  */
280	      if (try_kmp
281		  && outer_loop_count >= 10
282		  && comparison_count >= 5 * outer_loop_count)
283		{
284		  /* See if needle + comparison_count now reaches the end of
285		     needle.  */
286		  size_t count = comparison_count - last_ccount;
287		  for (;
288		       count > 0 && mbui_avail (iter_needle_last_ccount);
289		       count--)
290		    mbui_advance (iter_needle_last_ccount);
291		  last_ccount = comparison_count;
292		  if (!mbui_avail (iter_needle_last_ccount))
293		    {
294		      /* Try the Knuth-Morris-Pratt algorithm.  */
295		      const char *result;
296		      bool success =
297			knuth_morris_pratt_multibyte (haystack, needle,
298						      &result);
299		      if (success)
300			return (char *) result;
301		      try_kmp = false;
302		    }
303		}
304
305	      outer_loop_count++;
306	      comparison_count++;
307	      if (mb_equal (mbui_cur (iter_haystack), mbui_cur (iter_needle)))
308		/* The first character matches.  */
309		{
310		  mbui_iterator_t rhaystack;
311		  mbui_iterator_t rneedle;
312
313		  memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t));
314		  mbui_advance (rhaystack);
315
316		  mbui_init (rneedle, needle);
317		  if (!mbui_avail (rneedle))
318		    abort ();
319		  mbui_advance (rneedle);
320
321		  for (;; mbui_advance (rhaystack), mbui_advance (rneedle))
322		    {
323		      if (!mbui_avail (rneedle))
324			/* Found a match.  */
325			return (char *) mbui_cur_ptr (iter_haystack);
326		      if (!mbui_avail (rhaystack))
327			/* No match.  */
328			return NULL;
329		      comparison_count++;
330		      if (!mb_equal (mbui_cur (rhaystack), mbui_cur (rneedle)))
331			/* Nothing in this round.  */
332			break;
333		    }
334		}
335	    }
336	}
337      else
338	return (char *) haystack;
339    }
340  else
341#endif
342    {
343      if (*needle != '\0')
344	{
345	  /* Minimizing the worst-case complexity:
346	     Let n = strlen(haystack), m = strlen(needle).
347	     The na��ve algorithm is O(n*m) worst-case.
348	     The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
349	     memory allocation.
350	     To achieve linear complexity and yet amortize the cost of the
351	     memory allocation, we activate the Knuth-Morris-Pratt algorithm
352	     only once the na��ve algorithm has already run for some time; more
353	     precisely, when
354	       - the outer loop count is >= 10,
355	       - the average number of comparisons per outer loop is >= 5,
356	       - the total number of comparisons is >= m.
357	     But we try it only once.  If the memory allocation attempt failed,
358	     we don't retry it.  */
359	  bool try_kmp = true;
360	  size_t outer_loop_count = 0;
361	  size_t comparison_count = 0;
362	  size_t last_ccount = 0;		   /* last comparison count */
363	  const char *needle_last_ccount = needle; /* = needle + last_ccount */
364
365	  /* Speed up the following searches of needle by caching its first
366	     character.  */
367	  char b = *needle++;
368
369	  for (;; haystack++)
370	    {
371	      if (*haystack == '\0')
372		/* No match.  */
373		return NULL;
374
375	      /* See whether it's advisable to use an asymptotically faster
376		 algorithm.  */
377	      if (try_kmp
378		  && outer_loop_count >= 10
379		  && comparison_count >= 5 * outer_loop_count)
380		{
381		  /* See if needle + comparison_count now reaches the end of
382		     needle.  */
383		  if (needle_last_ccount != NULL)
384		    {
385		      needle_last_ccount +=
386			strnlen (needle_last_ccount,
387				 comparison_count - last_ccount);
388		      if (*needle_last_ccount == '\0')
389			needle_last_ccount = NULL;
390		      last_ccount = comparison_count;
391		    }
392		  if (needle_last_ccount == NULL)
393		    {
394		      /* Try the Knuth-Morris-Pratt algorithm.  */
395		      const char *result;
396		      bool success =
397			knuth_morris_pratt_unibyte (haystack, needle - 1,
398						    &result);
399		      if (success)
400			return (char *) result;
401		      try_kmp = false;
402		    }
403		}
404
405	      outer_loop_count++;
406	      comparison_count++;
407	      if (*haystack == b)
408		/* The first character matches.  */
409		{
410		  const char *rhaystack = haystack + 1;
411		  const char *rneedle = needle;
412
413		  for (;; rhaystack++, rneedle++)
414		    {
415		      if (*rneedle == '\0')
416			/* Found a match.  */
417			return (char *) haystack;
418		      if (*rhaystack == '\0')
419			/* No match.  */
420			return NULL;
421		      comparison_count++;
422		      if (*rhaystack != *rneedle)
423			/* Nothing in this round.  */
424			break;
425		    }
426		}
427	    }
428	}
429      else
430	return (char *) haystack;
431    }
432}
433