/*
tre-match-backtrack.c - TRE backtracking regex matching engine
This software is released under a BSD-style license.
See the file LICENSE for details and copyright.
*/
/*
This matcher is for regexps that use back referencing. Regexp matching
with back referencing is an NP-complete problem on the number of back
references. The easiest way to match them is to use a backtracking
routine which basically goes through all possible paths in the TNFA
and chooses the one which results in the best (leftmost and longest)
match. This can be spectacularly expensive and may run out of stack
space, but there really is no better known generic algorithm. Quoting
Henry Spencer from comp.compilers:
<URL: http://compilers.iecc.com/comparch/article/93-03-102>
POSIX.2 REs require longest match, which is really exciting to
implement since the obsolete ("basic") variant also includes
\<digit>. I haven't found a better way of tackling this than doing
a preliminary match using a DFA (or simulation) on a modified RE
that just replicates subREs for \<digit>, and then doing a
backtracking match to determine whether the subRE matches were
right. This can be rather slow, but I console myself with the
thought that people who use \<digit> deserve very slow execution.
(Pun unintentional but very appropriate.)
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /* HAVE_CONFIG_H */
#include "tre-alloca.h"
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#ifdef HAVE_WCHAR_H
#include <wchar.h>
#endif /* HAVE_WCHAR_H */
#ifdef HAVE_WCTYPE_H
#include <wctype.h>
#endif /* HAVE_WCTYPE_H */
#ifndef TRE_WCHAR
#include <ctype.h>
#endif /* !TRE_WCHAR */
#ifdef HAVE_MALLOC_H
#include <malloc.h>
#endif /* HAVE_MALLOC_H */
#include "tre-internal.h"
#include "tre-mem.h"
#include "tre-match-utils.h"
#include "tre.h"
#include "xmalloc.h"
typedef struct {
int pos;
const char *str_byte;
#ifdef TRE_WCHAR
const wchar_t *str_wide;
#endif /* TRE_WCHAR */
tre_tnfa_transition_t *state;
int state_id;
int next_c;
int *tags;
#ifdef TRE_MBSTATE
mbstate_t mbstate;
#endif /* TRE_MBSTATE */
} tre_backtrack_item_t;
typedef struct tre_backtrack_struct {
tre_backtrack_item_t item;
struct tre_backtrack_struct *prev;
struct tre_backtrack_struct *next;
} *tre_backtrack_t;
#ifdef TRE_WCHAR
#define BT_STACK_WIDE_IN(_str_wide) stack->item.str_wide = (_str_wide)
#define BT_STACK_WIDE_OUT (str_wide) = stack->item.str_wide
#else /* !TRE_WCHAR */
#define BT_STACK_WIDE_IN(_str_wide)
#define BT_STACK_WIDE_OUT
#endif /* !TRE_WCHAR */
#ifdef TRE_MBSTATE
#define BT_STACK_MBSTATE_IN stack->item.mbstate = (mbstate)
#define BT_STACK_MBSTATE_OUT (mbstate) = stack->item.mbstate
#else /* !TRE_MBSTATE */
#define BT_STACK_MBSTATE_IN
#define BT_STACK_MBSTATE_OUT
#endif /* !TRE_MBSTATE */
#ifdef TRE_USE_ALLOCA
#define tre_bt_mem_new tre_mem_newa
#define tre_bt_mem_alloc tre_mem_alloca
#define tre_bt_mem_destroy(obj) do { } while (/*CONSTCOND*/(void)0,0)
#else /* !TRE_USE_ALLOCA */
#define tre_bt_mem_new tre_mem_new
#define tre_bt_mem_alloc tre_mem_alloc
#define tre_bt_mem_destroy tre_mem_destroy
#endif /* !TRE_USE_ALLOCA */
#define BT_STACK_PUSH(_pos, _str_byte, _str_wide, _state, _state_id, _next_c, _tags, _mbstate) \
do \
{ \
size_t i; \
if (!stack->next) \
{ \
tre_backtrack_t s; \
s = tre_bt_mem_alloc(mem, sizeof(*s)); \
if (!s) \
{ \
tre_bt_mem_destroy(mem); \
if (tags) \
xfree(tags); \
if (pmatch) \
xfree(pmatch); \
if (states_seen) \
xfree(states_seen); \
return REG_ESPACE; \
} \
s->prev = stack; \
s->next = NULL; \
s->item.tags = tre_bt_mem_alloc(mem, \
sizeof(*tags) * tnfa->num_tags); \
if (!s->item.tags) \
{ \
tre_bt_mem_destroy(mem); \
if (tags) \
xfree(tags); \
if (pmatch) \
xfree(pmatch); \
if (states_seen) \
xfree(states_seen); \
return REG_ESPACE; \
} \
stack->next = s; \
stack = s; \
} \
else \
stack = stack->next; \
stack->item.pos = (_pos); \
stack->item.str_byte = (_str_byte); \
BT_STACK_WIDE_IN(_str_wide); \
stack->item.state = (_state); \
stack->item.state_id = (_state_id); \
stack->item.next_c = (_next_c); \
for (i = 0; i < tnfa->num_tags; i++) \
stack->item.tags[i] = (_tags)[i]; \
BT_STACK_MBSTATE_IN; \
} \
while (/*CONSTCOND*/(void)0,0)
#define BT_STACK_POP() \
do \
{ \
size_t i; \
assert(stack->prev); \
pos = stack->item.pos; \
if (type == STR_USER) \
str_source->rewind(pos + pos_add_next, str_source->context); \
str_byte = stack->item.str_byte; \
BT_STACK_WIDE_OUT; \
state = stack->item.state; \
next_c = (tre_char_t) stack->item.next_c; \
for (i = 0; i < tnfa->num_tags; i++) \
tags[i] = stack->item.tags[i]; \
BT_STACK_MBSTATE_OUT; \
stack = stack->prev; \
} \
while (/*CONSTCOND*/(void)0,0)
#undef MIN
#define MIN(a, b) ((a) <= (b) ? (a) : (b))
reg_errcode_t
tre_tnfa_run_backtrack(const tre_tnfa_t *tnfa, const void *string,
int len, tre_str_type_t type, int *match_tags,
int eflags, int *match_end_ofs)
{
/* State variables required by GET_NEXT_WCHAR. */
tre_char_t prev_c = 0, next_c = 0;
const char *str_byte = string;
int pos = 0;
unsigned int pos_add_next = 1;
#ifdef TRE_WCHAR
const wchar_t *str_wide = string;
#ifdef TRE_MBSTATE
mbstate_t mbstate;
#endif /* TRE_MBSTATE */
#endif /* TRE_WCHAR */
int reg_notbol = eflags & REG_NOTBOL;
int reg_noteol = eflags & REG_NOTEOL;
int reg_newline = tnfa->cflags & REG_NEWLINE;
size_t str_user_end = 0;
/* These are used to remember the necessary values of the above
variables to return to the position where the current search
started from. */
int next_c_start;
const char *str_byte_start;
int pos_start = -1;
#ifdef TRE_WCHAR
const wchar_t *str_wide_start;
#endif /* TRE_WCHAR */
#ifdef TRE_MBSTATE
mbstate_t mbstate_start;
#endif /* TRE_MBSTATE */
/* End offset of best match so far, or -1 if no match found yet. */
int match_eo = -1;
/* Tag arrays. */
int *next_tags, *tags = NULL;
/* Current TNFA state. */
tre_tnfa_transition_t *state;
int *states_seen = NULL;
/* Memory allocator to for allocating the backtracking stack. */
tre_mem_t mem = tre_bt_mem_new();
/* The backtracking stack. */
tre_backtrack_t stack;
tre_tnfa_transition_t *trans_i;
regmatch_t *pmatch = NULL;
reg_errcode_t ret;
#ifdef TRE_MBSTATE
memset(&mbstate, '\0', sizeof(mbstate));
#endif /* TRE_MBSTATE */
if (!mem)
return REG_ESPACE;
stack = tre_bt_mem_alloc(mem, sizeof(*stack));
if (!stack)
{
ret = REG_ESPACE;
goto error_exit;
}
stack->prev = NULL;
stack->next = NULL;
DPRINT(("tnfa_execute_backtrack, input type %d\n", type));
DPRINT(("len = %d\n", len));
#ifdef TRE_USE_ALLOCA
tags = alloca(sizeof(*tags) * tnfa->num_tags);
pmatch = alloca(sizeof(*pmatch) * tnfa->num_submatches);
states_seen = alloca(sizeof(*states_seen) * tnfa->num_states);
#else /* !TRE_USE_ALLOCA */
if (tnfa->num_tags)
{
tags = xmalloc(sizeof(*tags) * tnfa->num_tags);
if (!tags)
{
ret = REG_ESPACE;
goto error_exit;
}
}
if (tnfa->num_submatches)
{
pmatch = xmalloc(sizeof(*pmatch) * tnfa->num_submatches);
if (!pmatch)
{
ret = REG_ESPACE;
goto error_exit;
}
}
if (tnfa->num_states)
{
states_seen = xmalloc(sizeof(*states_seen) * tnfa->num_states);
if (!states_seen)
{
ret = REG_ESPACE;
goto error_exit;
}
}
#endif /* !TRE_USE_ALLOCA */
retry:
{
size_t i;
for (i = 0; i < tnfa->num_tags; i++)
{
tags[i] = -1;
if (match_tags)
match_tags[i] = -1;
}
for (i = 0; i < tnfa->num_states; i++)
states_seen[i] = 0;
}
state = NULL;
pos = pos_start;
if (type == STR_USER)
str_source->rewind(pos + pos_add_next, str_source->context);
GET_NEXT_WCHAR();
pos_start = pos;
next_c_start = next_c;
str_byte_start = str_byte;
#ifdef TRE_WCHAR
str_wide_start = str_wide;
#endif /* TRE_WCHAR */
#ifdef TRE_MBSTATE
mbstate_start = mbstate;
#endif /* TRE_MBSTATE */
/* Handle initial states. */
next_tags = NULL;
for (trans_i = tnfa->initial; trans_i->state; trans_i++)
{
DPRINT(("> init %p, prev_c %lc\n", trans_i->state, (tre_cint_t)prev_c));
if (trans_i->assertions && CHECK_ASSERTIONS(trans_i->assertions))
{
DPRINT(("assert failed\n"));
continue;
}
if (state == NULL)
{
/* Start from this state. */
state = trans_i->state;
next_tags = trans_i->tags;
}
else
{
/* Backtrack to this state. */
DPRINT(("saving state %d for backtracking\n", trans_i->state_id));
BT_STACK_PUSH(pos, str_byte, str_wide, trans_i->state,
trans_i->state_id, next_c, tags, mbstate);
{
int *tmp = trans_i->tags;
if (tmp)
while (*tmp >= 0)
stack->item.tags[*tmp++] = pos;
}
}
}
if (next_tags)
for (; *next_tags >= 0; next_tags++)
tags[*next_tags] = pos;
DPRINT(("entering match loop, pos %d, str_byte %p\n", pos, str_byte));
DPRINT(("pos:chr/code | state and tags\n"));
DPRINT(("-------------+------------------------------------------------\n"));
if (state == NULL)
goto backtrack;
while (/*CONSTCOND*/(void)1,1)
{
tre_tnfa_transition_t *next_state;
int empty_br_match;
DPRINT(("start loop\n"));
if (state == tnfa->final)
{
DPRINT((" match found, %d %d\n", match_eo, pos));
if (match_eo < pos
|| (match_eo == pos
&& match_tags
&& tre_tag_order(tnfa->num_tags, tnfa->tag_directions,
tags, match_tags)))
{
size_t i;
/* This match wins the previous match. */
DPRINT((" win previous\n"));
match_eo = pos;
if (match_tags)
for (i = 0; i < tnfa->num_tags; i++)
match_tags[i] = tags[i];
}
/* Our TNFAs never have transitions leaving from the final state,
so we jump right to backtracking. */
goto backtrack;
}
#ifdef TRE_DEBUG
DPRINT(("%3d:%2lc/%05d | %p ", pos, (tre_cint_t)next_c, (int)next_c,
state));
{
int i;
for (i = 0; i < tnfa->num_tags; i++)
DPRINT(("%d%s", tags[i], i < tnfa->num_tags - 1 ? ", " : ""));
DPRINT(("\n"));
}
#endif /* TRE_DEBUG */
/* Go to the next character in the input string. */
empty_br_match = 0;
trans_i = state;
if (trans_i->state && trans_i->assertions & ASSERT_BACKREF)
{
/* This is a back reference state. All transitions leaving from
this state have the same back reference "assertion". Instead
of reading the next character, we match the back reference. */
regoff_t so, eo, bt = trans_i->u.backref;
regoff_t bt_len;
regoff_t result;
DPRINT((" should match back reference %d\n", bt));
/* Get the substring we need to match against. Remember to
turn off REG_NOSUB temporarily. */
tre_fill_pmatch(bt + 1, pmatch, tnfa->cflags & ~REG_NOSUB,
tnfa, tags, pos);
/* LINTED */so = pmatch[bt].rm_so;
/* LINTED */eo = pmatch[bt].rm_eo;
bt_len = eo - so;
#ifdef TRE_DEBUG
{
int slen;
if (len < 0)
slen = bt_len;
else
slen = MIN(bt_len, len - pos);
if (type == STR_BYTE)
{
DPRINT((" substring (len %d) is [%d, %d[: '%.*s'\n",
bt_len, so, eo, bt_len, (char*)string + so));
DPRINT((" current string is '%.*s'\n", slen, str_byte - 1));
}
#ifdef TRE_WCHAR
else if (type == STR_WIDE)
{
DPRINT((" substring (len %d) is [%d, %d[: '%.*" STRF "'\n",
bt_len, so, eo, bt_len, (wchar_t*)string + so));
DPRINT((" current string is '%.*" STRF "'\n",
slen, str_wide - 1));
}
#endif /* TRE_WCHAR */
}
#endif
if (len < 0)
{
if (type == STR_USER)
result = str_source->compare((unsigned)so, (unsigned)pos,
(unsigned)bt_len,
str_source->context);
#ifdef TRE_WCHAR
else if (type == STR_WIDE)
result = wcsncmp((const wchar_t*)string + so, str_wide - 1,
(size_t)bt_len);
#endif /* TRE_WCHAR */
else
/* LINTED */result = strncmp((const char*)string + so, str_byte - 1,
(size_t)bt_len);
}
else if (len - pos < bt_len)
result = 1;
#ifdef TRE_WCHAR
else if (type == STR_WIDE)
result = wmemcmp((const wchar_t*)string + so, str_wide - 1,
(size_t)bt_len);
#endif /* TRE_WCHAR */
else
/* LINTED */result = memcmp((const char*)string + so, str_byte - 1,
(size_t)bt_len);
if (result == 0)
{
/* Back reference matched. Check for infinite loop. */
if (bt_len == 0)
empty_br_match = 1;
if (empty_br_match && states_seen[trans_i->state_id])
{
DPRINT((" avoid loop\n"));
goto backtrack;
}
states_seen[trans_i->state_id] = empty_br_match;
/* Advance in input string and resync `prev_c', `next_c'
and pos. */
DPRINT((" back reference matched\n"));
/* LINTED */str_byte += bt_len - 1;
#ifdef TRE_WCHAR
/* LINTED */str_wide += bt_len - 1;
#endif /* TRE_WCHAR */
/* LINTED */pos += bt_len - 1;
GET_NEXT_WCHAR();
DPRINT((" pos now %d\n", pos));
}
else
{
DPRINT((" back reference did not match\n"));
goto backtrack;
}
}
else
{
/* Check for end of string. */
if (len < 0)
{
if (type == STR_USER)
{
if (str_user_end)
goto backtrack;
}
else if (next_c == L'\0')
goto backtrack;
}
else
{
if (pos >= len)
goto backtrack;
}
/* Read the next character. */
GET_NEXT_WCHAR();
}
next_state = NULL;
for (trans_i = state; trans_i->state; trans_i++)
{
DPRINT((" transition %d-%d (%c-%c) %d to %d\n",
trans_i->code_min, trans_i->code_max,
trans_i->code_min, trans_i->code_max,
trans_i->assertions, trans_i->state_id));
if (trans_i->code_min <= (tre_cint_t)prev_c
&& trans_i->code_max >= (tre_cint_t)prev_c)
{
if (trans_i->assertions
&& (CHECK_ASSERTIONS(trans_i->assertions)
|| CHECK_CHAR_CLASSES(trans_i, tnfa, eflags)))
{
DPRINT((" assertion failed\n"));
continue;
}
if (next_state == NULL)
{
/* First matching transition. */
DPRINT((" Next state is %d\n", trans_i->state_id));
next_state = trans_i->state;
next_tags = trans_i->tags;
}
else
{
/* Second matching transition. We may need to backtrack here
to take this transition instead of the first one, so we
push this transition in the backtracking stack so we can
jump back here if needed. */
DPRINT((" saving state %d for backtracking\n",
trans_i->state_id));
BT_STACK_PUSH(pos, str_byte, str_wide, trans_i->state,
trans_i->state_id, next_c, tags, mbstate);
{
int *tmp;
for (tmp = trans_i->tags; tmp && *tmp >= 0; tmp++)
stack->item.tags[*tmp] = pos;
}
#if 0 /* XXX - it's important not to look at all transitions here to keep
the stack small! */
break;
#endif
}
}
}
if (next_state != NULL)
{
/* Matching transitions were found. Take the first one. */
state = next_state;
/* Update the tag values. */
if (next_tags)
while (*next_tags >= 0)
tags[*next_tags++] = pos;
}
else
{
backtrack:
/* A matching transition was not found. Try to backtrack. */
if (stack->prev)
{
DPRINT((" backtracking\n"));
#if ASSERT_BACKREF
if (stack->item.state->assertions)
{
DPRINT((" states_seen[%d] = 0\n",
stack->item.state_id));
states_seen[stack->item.state_id] = 0;
}
#endif
BT_STACK_POP();
}
else if (match_eo < 0)
{
/* Try starting from a later position in the input string. */
/* Check for end of string. */
if (len < 0)
{
if (next_c == L'\0')
{
DPRINT(("end of string.\n"));
break;
}
}
else
{
if (pos >= len)
{
DPRINT(("end of string.\n"));
break;
}
}
DPRINT(("restarting from next start position\n"));
next_c = (tre_char_t) next_c_start;
#ifdef TRE_MBSTATE
mbstate = mbstate_start;
#endif /* TRE_MBSTATE */
str_byte = str_byte_start;
#ifdef TRE_WCHAR
str_wide = str_wide_start;
#endif /* TRE_WCHAR */
goto retry;
}
else
{
DPRINT(("finished\n"));
break;
}
}
}
ret = match_eo >= 0 ? REG_OK : REG_NOMATCH;
*match_end_ofs = match_eo;
error_exit:
tre_bt_mem_destroy(mem);
#ifndef TRE_USE_ALLOCA
if (tags)
xfree(tags);
if (pmatch)
xfree(pmatch);
if (states_seen)
xfree(states_seen);
#endif /* !TRE_USE_ALLOCA */
return ret;
}