/[pcre]/code/trunk/pcre_dfa_exec.c
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revision 428 by ph10, Mon Aug 31 17:10:26 2009 UTC revision 442 by ph10, Fri Sep 11 10:21:02 2009 UTC
# Line 45  FSM). This is NOT Perl- compatible, but Line 45  FSM). This is NOT Perl- compatible, but
45  applications. */  applications. */
46    
47    
48    /* NOTE ABOUT PERFORMANCE: A user of this function sent some code that improved
49    the performance of his patterns greatly. I could not use it as it stood, as it
50    was not thread safe, and made assumptions about pattern sizes. Also, it caused
51    test 7 to loop, and test 9 to crash with a segfault.
52    
53    The issue is the check for duplicate states, which is done by a simple linear
54    search up the state list. (Grep for "duplicate" below to find the code.) For
55    many patterns, there will never be many states active at one time, so a simple
56    linear search is fine. In patterns that have many active states, it might be a
57    bottleneck. The suggested code used an indexing scheme to remember which states
58    had previously been used for each character, and avoided the linear search when
59    it knew there was no chance of a duplicate. This was implemented when adding
60    states to the state lists.
61    
62    I wrote some thread-safe, not-limited code to try something similar at the time
63    of checking for duplicates (instead of when adding states), using index vectors
64    on the stack. It did give a 13% improvement with one specially constructed
65    pattern for certain subject strings, but on other strings and on many of the
66    simpler patterns in the test suite it did worse. The major problem, I think,
67    was the extra time to initialize the index. This had to be done for each call
68    of internal_dfa_exec(). (The supplied patch used a static vector, initialized
69    only once - I suspect this was the cause of the problems with the tests.)
70    
71    Overall, I concluded that the gains in some cases did not outweigh the losses
72    in others, so I abandoned this code. */
73    
74    
75    
76  #ifdef HAVE_CONFIG_H  #ifdef HAVE_CONFIG_H
77  #include "config.h"  #include "config.h"
78  #endif  #endif
# Line 389  if (*first_op == OP_REVERSE) Line 417  if (*first_op == OP_REVERSE)
417        current_subject - start_subject : max_back;        current_subject - start_subject : max_back;
418      current_subject -= gone_back;      current_subject -= gone_back;
419      }      }
420    
421      /* Save the earliest consulted character */
422    
423      if (current_subject < md->start_used_ptr)
424        md->start_used_ptr = current_subject;
425    
426    /* Now we can process the individual branches. */    /* Now we can process the individual branches. */
427    
# Line 545  for (;;) Line 578  for (;;)
578          }          }
579        }        }
580    
581      /* Check for a duplicate state with the same count, and skip if found. */      /* Check for a duplicate state with the same count, and skip if found.
582        See the note at the head of this module about the possibility of improving
583        performance here. */
584    
585      for (j = 0; j < i; j++)      for (j = 0; j < i; j++)
586        {        {
# Line 612  for (;;) Line 647  for (;;)
647  /* ========================================================================== */  /* ========================================================================== */
648        /* Reached a closing bracket. If not at the end of the pattern, carry        /* Reached a closing bracket. If not at the end of the pattern, carry
649        on with the next opcode. Otherwise, unless we have an empty string and        on with the next opcode. Otherwise, unless we have an empty string and
650        PCRE_NOTEMPTY is set, save the match data, shifting up all previous        PCRE_NOTEMPTY is set, or PCRE_NOTEMPTY_ATSTART is set and we are at the
651          start of the subject, save the match data, shifting up all previous
652        matches so we always have the longest first. */        matches so we always have the longest first. */
653    
654        case OP_KET:        case OP_KET:
# Line 629  for (;;) Line 665  for (;;)
665        else        else
666          {          {
667          reached_end++;    /* Count branches that reach the end */          reached_end++;    /* Count branches that reach the end */
668          if (ptr > current_subject || (md->moptions & PCRE_NOTEMPTY) == 0)          if (ptr > current_subject ||
669                ((md->moptions & PCRE_NOTEMPTY) == 0 &&
670                  ((md->moptions & PCRE_NOTEMPTY_ATSTART) == 0 ||
671                    current_subject > start_subject + md->start_offset)))
672            {            {
673            if (match_count < 0) match_count = (offsetcount >= 2)? 1 : 0;            if (match_count < 0) match_count = (offsetcount >= 2)? 1 : 0;
674              else if (match_count > 0 && ++match_count * 2 >= offsetcount)              else if (match_count > 0 && ++match_count * 2 >= offsetcount)
# Line 800  for (;;) Line 839  for (;;)
839          if (ptr > start_subject)          if (ptr > start_subject)
840            {            {
841            const uschar *temp = ptr - 1;            const uschar *temp = ptr - 1;
842              if (temp < md->start_used_ptr) md->start_used_ptr = temp;
843  #ifdef SUPPORT_UTF8  #ifdef SUPPORT_UTF8
844            if (utf8) BACKCHAR(temp);            if (utf8) BACKCHAR(temp);
845  #endif  #endif
# Line 2503  for (;;) Line 2543  for (;;)
2543        {        {
2544        if (offsetcount >= 2)        if (offsetcount >= 2)
2545          {          {
2546          offsets[0] = current_subject - start_subject;          offsets[0] = md->start_used_ptr - start_subject;
2547          offsets[1] = end_subject - start_subject;          offsets[1] = end_subject - start_subject;
2548          }          }
2549        match_count = PCRE_ERROR_PARTIAL;        match_count = PCRE_ERROR_PARTIAL;
# Line 2645  md->start_code = (const uschar *)argumen Line 2685  md->start_code = (const uschar *)argumen
2685      re->name_table_offset + re->name_count * re->name_entry_size;      re->name_table_offset + re->name_count * re->name_entry_size;
2686  md->start_subject = (const unsigned char *)subject;  md->start_subject = (const unsigned char *)subject;
2687  md->end_subject = end_subject;  md->end_subject = end_subject;
2688    md->start_offset = start_offset;
2689  md->moptions = options;  md->moptions = options;
2690  md->poptions = re->options;  md->poptions = re->options;
2691    
# Line 2936  for (;;) Line 2977  for (;;)
2977    
2978    /* OK, now we can do the business */    /* OK, now we can do the business */
2979    
2980      md->start_used_ptr = current_subject;
2981    
2982    rc = internal_dfa_exec(    rc = internal_dfa_exec(
2983      md,                                /* fixed match data */      md,                                /* fixed match data */
2984      md->start_code,                    /* this subexpression's code */      md->start_code,                    /* this subexpression's code */
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