Re: WIP: lookbehind constraints for our regexp engine - Mailing list pgsql-hackers
| From | Tom Lane |
|---|---|
| Subject | Re: WIP: lookbehind constraints for our regexp engine |
| Date | |
| Msg-id | 1662.1446068070@sss.pgh.pa.us Whole thread Raw |
| In response to | WIP: lookbehind constraints for our regexp engine (Tom Lane <tgl@sss.pgh.pa.us>) |
| List | pgsql-hackers |
I wrote:
> I've occasionally heard complaints that our regex engine only has
> lookahead constraints not lookbehind constraints, while Perl's for example
> does have those. While I was fooling around with the other issues in that
> code, I learned enough to realize that it would not be that hard to
> implement such things, and the attached proof-of-concept patch does so
> (using Perl-compatible syntax, in case you're wondering).
> However, I don't feel like this is done to the point of being committable,
> because its performance leaves something to be desired in a lot of cases.
> The difficulty is that because the engine can only match in a forward
> direction, in the worst case you have to check a lookbehind constraint by
> trying to match starting from the string start to see if a match exists
> ending at the current-location where you're testing the constraint. That
> makes it, worst case, O(N^2) to search a string of length N.
Attached is an updated patch that eliminates the O(N^2) performance issue
by creating a third version of the core text-matching functions (previously
just longest() and shortest()). This new version is able to suspend and
resume a scan without significant overhead, and it reports whether a match
exists ending at the current stop point. So we effectively run a
lookbehind constraint's NFA over the string just once, no matter how many
places we actually need to check the constraint's satisfaction at.
This is still not fast in an absolute sense: the limiting scan rate for a
pattern with leading lookbehind constraint (which means the constraint
must be checked at each character) seems to be roughly 10X slower than
for simple constraint-free patterns. For example
regression=# select repeat('xyzzy', 1000000) ~ '(?<=xy)y';
?column?
----------
f
(1 row)
Time: 601.079 ms
regression=# select repeat('xyzzy', 1000000) ~ 'xyy';
?column?
----------
f
(1 row)
Time: 64.213 ms
(As a comparison point, perl 5.10.1 does the same searches in about 250ms
and 30ms respectively; though I'm not comparing apples to oranges exactly
since this is a debug build of PG versus production perl.)
This is not entirely the fault of the lookbehind code, though; most of the
cycles are being spent in miss() in the outer DFA scan, not in checking
the LACON itself. That's a consequence of Henry Spencer's decision that
any state transition involving a LACON check should be treated as a cache
miss. It's not terribly hard to imagine having a code path like "check
this LACON and go to one of two cached states depending on whether it
succeeds". However, I couldn't figure a way to shoehorn that into the
code without adding both cycles to the basic text search loops and bloat
to the stateset cache data structure, costs that would be paid whether or
not you're actually using any LACONs. So maybe Henry made the right
optimization tradeoff.
Also, I put in a compile-time optimization for lookbehind (and lookahead)
constraints that consist of just a single character or bracket expression,
eg these run at about the speed of a simple pattern:
regression=# select repeat('xyzzy', 1000000) ~ '(?<=[ab])y';
?column?
----------
f
(1 row)
Time: 51.936 ms
regression=# select repeat('xyzzy', 1000000) ~ '(?<![xz])y';
?column?
----------
f
(1 row)
Time: 56.149 ms
That's feasible because the constraint can be reduced to a BEHIND (or
AHEAD) constraint, which was a concept that already existed in Henry's
code and doesn't need the LACON machinery at all. (Perl doesn't seem to
have any comparable optimization, btw, so that we are actually beating it
by a wide margin in these cases. Not to mention it fails entirely on
variable-length lookbehind patterns.)
In any case I think this is now a credible candidate to commit as-is.
Making lookbehinds go still faster is likely not the most useful place
to put in effort if someone is looking to micro-optimize regex execution
speed.
Comments?
regards, tom lane
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 2946122..4d482ec 100644
*** a/doc/src/sgml/func.sgml
--- b/doc/src/sgml/func.sgml
*************** SELECT foo FROM regexp_split_to_table('t
*** 4477,4489 ****
where no substring matching <replaceable>re</> begins
(AREs only) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
! Lookahead constraints cannot contain <firstterm>back references</>
! (see <xref linkend="posix-escape-sequences">),
and all parentheses within them are considered non-capturing.
</para>
</sect3>
--- 4477,4503 ----
where no substring matching <replaceable>re</> begins
(AREs only) </entry>
</row>
+
+ <row>
+ <entry> <literal>(?<=</><replaceable>re</><literal>)</> </entry>
+ <entry> <firstterm>positive lookbehind</> matches at any point
+ where a substring matching <replaceable>re</> ends
+ (AREs only) </entry>
+ </row>
+
+ <row>
+ <entry> <literal>(?<!</><replaceable>re</><literal>)</> </entry>
+ <entry> <firstterm>negative lookbehind</> matches at any point
+ where no substring matching <replaceable>re</> ends
+ (AREs only) </entry>
+ </row>
</tbody>
</tgroup>
</table>
<para>
! Lookahead and lookbehind constraints cannot contain <firstterm>back
! references</> (see <xref linkend="posix-escape-sequences">),
and all parentheses within them are considered non-capturing.
</para>
</sect3>
*************** SELECT regexp_matches('abc01234xyz', '(?
*** 5355,5361 ****
the lack of special treatment for a trailing newline,
the addition of complemented bracket expressions to the things
affected by newline-sensitive matching,
! the restrictions on parentheses and back references in lookahead
constraints, and the longest/shortest-match (rather than first-match)
matching semantics.
</para>
--- 5369,5375 ----
the lack of special treatment for a trailing newline,
the addition of complemented bracket expressions to the things
affected by newline-sensitive matching,
! the restrictions on parentheses and back references in lookahead/lookbehind
constraints, and the longest/shortest-match (rather than first-match)
matching semantics.
</para>
diff --git a/src/backend/regex/README b/src/backend/regex/README
index 5c24d3d..6c9f483 100644
*** a/src/backend/regex/README
--- b/src/backend/regex/README
*************** The possible arc types are:
*** 332,341 ****
as "$0->to_state" or "$1->to_state" for end-of-string and end-of-line
constraints respectively.
! LACON constraints, which represent "(?=re)" and "(?!re)" constraints,
! i.e. the input starting at this point must match (or not match) a
! given sub-RE, but the matching input is not consumed. These are
! dumped as ":subtree_number:->to_state".
If you see anything else (especially any question marks) in the display of
an arc, it's dumpnfa() trying to tell you that there's something fishy
--- 332,341 ----
as "$0->to_state" or "$1->to_state" for end-of-string and end-of-line
constraints respectively.
! LACON constraints, which represent "(?=re)", "(?!re)", "(?<=re)", and
! "(?<!re)" constraints, i.e. the input starting/ending at this point must
! match (or not match) a given sub-RE, but the matching input is not
! consumed. These are dumped as ":subtree_number:->to_state".
If you see anything else (especially any question marks) in the display of
an arc, it's dumpnfa() trying to tell you that there's something fishy
diff --git a/src/backend/regex/re_syntax.n b/src/backend/regex/re_syntax.n
index f37bb85..4621bfc 100644
*** a/src/backend/regex/re_syntax.n
--- b/src/backend/regex/re_syntax.n
*************** where a substring matching \fIre\fR begi
*** 196,205 ****
\fB(?!\fIre\fB)\fR
\fInegative lookahead\fR (AREs only), matches at any point
where no substring matching \fIre\fR begins
.RE
.PP
! The lookahead constraints may not contain back references (see later),
! and all parentheses within them are considered non-capturing.
.PP
An RE may not end with `\fB\e\fR'.
--- 196,213 ----
\fB(?!\fIre\fB)\fR
\fInegative lookahead\fR (AREs only), matches at any point
where no substring matching \fIre\fR begins
+ .TP
+ \fB(?<=\fIre\fB)\fR
+ \fIpositive lookbehind\fR (AREs only), matches at any point
+ where a substring matching \fIre\fR ends
+ .TP
+ \fB(?<!\fIre\fB)\fR
+ \fInegative lookbehind\fR (AREs only), matches at any point
+ where no substring matching \fIre\fR ends
.RE
.PP
! Lookahead and lookbehind constraints may not contain back references
! (see later), and all parentheses within them are considered non-capturing.
.PP
An RE may not end with `\fB\e\fR'.
*************** Incompatibilities of note include `\fB\e
*** 856,862 ****
the lack of special treatment for a trailing newline,
the addition of complemented bracket expressions to the things
affected by newline-sensitive matching,
! the restrictions on parentheses and back references in lookahead constraints,
and the longest/shortest-match (rather than first-match) matching semantics.
.PP
The matching rules for REs containing both normal and non-greedy quantifiers
--- 864,871 ----
the lack of special treatment for a trailing newline,
the addition of complemented bracket expressions to the things
affected by newline-sensitive matching,
! the restrictions on parentheses and back references in lookahead/lookbehind
! constraints,
and the longest/shortest-match (rather than first-match) matching semantics.
.PP
The matching rules for REs containing both normal and non-greedy quantifiers
diff --git a/src/backend/regex/regc_lex.c b/src/backend/regex/regc_lex.c
index f6ed9f0..bfd9dcd 100644
*** a/src/backend/regex/regc_lex.c
--- b/src/backend/regex/regc_lex.c
*************** next(struct vars * v)
*** 582,587 ****
--- 582,589 ----
{
NOTE(REG_UNONPOSIX);
v->now++;
+ if (ATEOS())
+ FAILW(REG_BADRPT);
switch (*v->now++)
{
case CHR(':'): /* non-capturing paren */
*************** next(struct vars * v)
*** 596,607 ****
return next(v);
break;
case CHR('='): /* positive lookahead */
! NOTE(REG_ULOOKAHEAD);
! RETV(LACON, 1);
break;
case CHR('!'): /* negative lookahead */
! NOTE(REG_ULOOKAHEAD);
! RETV(LACON, 0);
break;
default:
FAILW(REG_BADRPT);
--- 598,628 ----
return next(v);
break;
case CHR('='): /* positive lookahead */
! NOTE(REG_ULOOKAROUND);
! RETV(LACON, LATYPE_AHEAD_POS);
break;
case CHR('!'): /* negative lookahead */
! NOTE(REG_ULOOKAROUND);
! RETV(LACON, LATYPE_AHEAD_NEG);
! break;
! case CHR('<'):
! if (ATEOS())
! FAILW(REG_BADRPT);
! switch (*v->now++)
! {
! case CHR('='): /* positive lookbehind */
! NOTE(REG_ULOOKAROUND);
! RETV(LACON, LATYPE_BEHIND_POS);
! break;
! case CHR('!'): /* negative lookbehind */
! NOTE(REG_ULOOKAROUND);
! RETV(LACON, LATYPE_BEHIND_NEG);
! break;
! default:
! FAILW(REG_BADRPT);
! break;
! }
! assert(NOTREACHED);
break;
default:
FAILW(REG_BADRPT);
diff --git a/src/backend/regex/regc_nfa.c b/src/backend/regex/regc_nfa.c
index 6f04321..7f0610a 100644
*** a/src/backend/regex/regc_nfa.c
--- b/src/backend/regex/regc_nfa.c
*************** cleartraverse(struct nfa * nfa,
*** 1349,1354 ****
--- 1349,1397 ----
}
/*
+ * single_color_transition - does getting from s1 to s2 cross one PLAIN arc?
+ *
+ * If traversing from s1 to s2 requires a single PLAIN match (possibly of any
+ * of a set of colors), return a state whose outarc list contains only PLAIN
+ * arcs of those color(s). Otherwise return NULL.
+ *
+ * This is used before optimizing the NFA, so there may be EMPTY arcs, which
+ * we should ignore; the possibility of an EMPTY is why the result state could
+ * be different from s1.
+ *
+ * It's worth troubling to handle multiple parallel PLAIN arcs here because a
+ * bracket construct such as [abc] might yield either one or several parallel
+ * PLAIN arcs depending on earlier atoms in the expression. We'd rather that
+ * that implementation detail not create user-visible performance differences.
+ */
+ static struct state *
+ single_color_transition(struct state * s1, struct state * s2)
+ {
+ struct arc *a;
+
+ /* Ignore leading EMPTY arc, if any, but 'ware loops */
+ if (s1->nouts == 1 && s1->outs->type == EMPTY && s1->outs->to != s1)
+ s1 = s1->outs->to;
+ /* Likewise for any trailing EMPTY arc */
+ if (s2->nins == 1 && s2->ins->type == EMPTY && s2->ins->from != s2)
+ s2 = s2->ins->from;
+ /* Perhaps we could have a single-state loop in between, if so reject */
+ if (s1 == s2)
+ return NULL;
+ /* s1 must have at least one outarc... */
+ if (s1->outs == NULL)
+ return NULL;
+ /* ... and they must all be PLAIN arcs to s2 */
+ for (a = s1->outs; a != NULL; a = a->outchain)
+ {
+ if (a->type != PLAIN || a->to != s2)
+ return NULL;
+ }
+ /* OK, return s1 as the possessor of the relevant outarcs */
+ return s1;
+ }
+
+ /*
* specialcolors - fill in special colors for an NFA
*/
static void
diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c
index b733bc7..aa759c2 100644
*** a/src/backend/regex/regcomp.c
--- b/src/backend/regex/regcomp.c
*************** static const chr *scanplain(struct vars
*** 57,62 ****
--- 57,64 ----
static void onechr(struct vars *, chr, struct state *, struct state *);
static void dovec(struct vars *, struct cvec *, struct state *, struct state *);
static void wordchrs(struct vars *);
+ static void processlacon(struct vars *, struct state *, struct state *, int,
+ struct state *, struct state *);
static struct subre *subre(struct vars *, int, int, struct state *, struct state *);
static void freesubre(struct vars *, struct subre *);
static void freesrnode(struct vars *, struct subre *);
*************** static int numst(struct subre *, int);
*** 65,71 ****
static void markst(struct subre *);
static void cleanst(struct vars *);
static long nfatree(struct vars *, struct subre *, FILE *);
! static long nfanode(struct vars *, struct subre *, FILE *);
static int newlacon(struct vars *, struct state *, struct state *, int);
static void freelacons(struct subre *, int);
static void rfree(regex_t *);
--- 67,73 ----
static void markst(struct subre *);
static void cleanst(struct vars *);
static long nfatree(struct vars *, struct subre *, FILE *);
! static long nfanode(struct vars *, struct subre *, int, FILE *);
static int newlacon(struct vars *, struct state *, struct state *, int);
static void freelacons(struct subre *, int);
static void rfree(regex_t *);
*************** static void deltraverse(struct nfa *, st
*** 146,151 ****
--- 148,154 ----
static void dupnfa(struct nfa *, struct state *, struct state *, struct state *, struct state *);
static void duptraverse(struct nfa *, struct state *, struct state *);
static void cleartraverse(struct nfa *, struct state *);
+ static struct state *single_color_transition(struct state *, struct state *);
static void specialcolors(struct nfa *);
static long optimize(struct nfa *, FILE *);
static void pullback(struct nfa *, FILE *);
*************** struct vars
*** 245,252 ****
int ntree; /* number of tree nodes, plus one */
struct cvec *cv; /* interface cvec */
struct cvec *cv2; /* utility cvec */
! struct subre *lacons; /* lookahead-constraint vector */
! int nlacons; /* size of lacons */
size_t spaceused; /* approx. space used for compilation */
};
--- 248,256 ----
int ntree; /* number of tree nodes, plus one */
struct cvec *cv; /* interface cvec */
struct cvec *cv2; /* utility cvec */
! struct subre *lacons; /* lookaround-constraint vector */
! int nlacons; /* size of lacons[]; note that only slots
! * numbered 1 .. nlacons-1 are used */
size_t spaceused; /* approx. space used for compilation */
};
*************** struct vars
*** 277,283 ****
#define CCLASS 'C' /* start of [: */
#define END 'X' /* end of [. [= [: */
#define RANGE 'R' /* - within [] which might be range delim. */
! #define LACON 'L' /* lookahead constraint subRE */
#define AHEAD 'a' /* color-lookahead arc */
#define BEHIND 'r' /* color-lookbehind arc */
#define WBDRY 'w' /* word boundary constraint */
--- 281,287 ----
#define CCLASS 'C' /* start of [: */
#define END 'X' /* end of [. [= [: */
#define RANGE 'R' /* - within [] which might be range delim. */
! #define LACON 'L' /* lookaround constraint subRE */
#define AHEAD 'a' /* color-lookahead arc */
#define BEHIND 'r' /* color-lookbehind arc */
#define WBDRY 'w' /* word boundary constraint */
*************** pg_regcomp(regex_t *re,
*** 432,442 ****
assert(v->nlacons == 0 || v->lacons != NULL);
for (i = 1; i < v->nlacons; i++)
{
#ifdef REG_DEBUG
if (debug != NULL)
fprintf(debug, "\n\n\n========= LA%d ==========\n", i);
#endif
! nfanode(v, &v->lacons[i], debug);
}
CNOERR();
if (v->tree->flags & SHORTER)
--- 436,450 ----
assert(v->nlacons == 0 || v->lacons != NULL);
for (i = 1; i < v->nlacons; i++)
{
+ struct subre *lasub = &v->lacons[i];
+
#ifdef REG_DEBUG
if (debug != NULL)
fprintf(debug, "\n\n\n========= LA%d ==========\n", i);
#endif
!
! /* Prepend .* to pattern if it's a lookbehind LACON */
! nfanode(v, lasub, !LATYPE_IS_AHEAD(lasub->subno), debug);
}
CNOERR();
if (v->tree->flags & SHORTER)
*************** makesearch(struct vars * v,
*** 640,646 ****
static struct subre *
parse(struct vars * v,
int stopper, /* EOS or ')' */
! int type, /* LACON (lookahead subRE) or PLAIN */
struct state * init, /* initial state */
struct state * final) /* final state */
{
--- 648,654 ----
static struct subre *
parse(struct vars * v,
int stopper, /* EOS or ')' */
! int type, /* LACON (lookaround subRE) or PLAIN */
struct state * init, /* initial state */
struct state * final) /* final state */
{
*************** parse(struct vars * v,
*** 719,725 ****
static struct subre *
parsebranch(struct vars * v,
int stopper, /* EOS or ')' */
! int type, /* LACON (lookahead subRE) or PLAIN */
struct state * left, /* leftmost state */
struct state * right, /* rightmost state */
int partial) /* is this only part of a branch? */
--- 727,733 ----
static struct subre *
parsebranch(struct vars * v,
int stopper, /* EOS or ')' */
! int type, /* LACON (lookaround subRE) or PLAIN */
struct state * left, /* leftmost state */
struct state * right, /* rightmost state */
int partial) /* is this only part of a branch? */
*************** parsebranch(struct vars * v,
*** 768,774 ****
static void
parseqatom(struct vars * v,
int stopper, /* EOS or ')' */
! int type, /* LACON (lookahead subRE) or PLAIN */
struct state * lp, /* left state to hang it on */
struct state * rp, /* right state to hang it on */
struct subre * top) /* subtree top */
--- 776,782 ----
static void
parseqatom(struct vars * v,
int stopper, /* EOS or ')' */
! int type, /* LACON (lookaround subRE) or PLAIN */
struct state * lp, /* left state to hang it on */
struct state * rp, /* right state to hang it on */
struct subre * top) /* subtree top */
*************** parseqatom(struct vars * v,
*** 782,788 ****
struct subre *atom; /* atom's subtree */
struct subre *t;
int cap; /* capturing parens? */
! int pos; /* positive lookahead? */
int subno; /* capturing-parens or backref number */
int atomtype;
int qprefer; /* quantifier short/long preference */
--- 790,796 ----
struct subre *atom; /* atom's subtree */
struct subre *t;
int cap; /* capturing parens? */
! int latype; /* lookaround constraint type */
int subno; /* capturing-parens or backref number */
int atomtype;
int qprefer; /* quantifier short/long preference */
*************** parseqatom(struct vars * v,
*** 866,884 ****
nonword(v, AHEAD, s, rp);
return;
break;
! case LACON: /* lookahead constraint */
! pos = v->nextvalue;
NEXT();
s = newstate(v->nfa);
s2 = newstate(v->nfa);
NOERR();
t = parse(v, ')', LACON, s, s2);
freesubre(v, t); /* internal structure irrelevant */
- assert(SEE(')') || ISERR());
- NEXT();
- n = newlacon(v, s, s2, pos);
NOERR();
! ARCV(LACON, n);
return;
break;
/* then errors, to get them out of the way */
--- 874,891 ----
nonword(v, AHEAD, s, rp);
return;
break;
! case LACON: /* lookaround constraint */
! latype = v->nextvalue;
NEXT();
s = newstate(v->nfa);
s2 = newstate(v->nfa);
NOERR();
t = parse(v, ')', LACON, s, s2);
freesubre(v, t); /* internal structure irrelevant */
NOERR();
! assert(SEE(')'));
! NEXT();
! processlacon(v, s, s2, latype, lp, rp);
return;
break;
/* then errors, to get them out of the way */
*************** wordchrs(struct vars * v)
*** 1634,1639 ****
--- 1641,1715 ----
}
/*
+ * processlacon - generate the NFA representation of a LACON
+ *
+ * In the general case this is just newlacon() + newarc(), but some cases
+ * can be optimized.
+ */
+ static void
+ processlacon(struct vars * v,
+ struct state * begin, /* start of parsed LACON sub-re */
+ struct state * end, /* end of parsed LACON sub-re */
+ int latype,
+ struct state * lp, /* left state to hang it on */
+ struct state * rp) /* right state to hang it on */
+ {
+ struct state *s1;
+ int n;
+
+ /*
+ * Check for lookaround RE consisting of a single plain color arc (or set
+ * of arcs); this would typically be a simple chr or a bracket expression.
+ */
+ s1 = single_color_transition(begin, end);
+ switch (latype)
+ {
+ case LATYPE_AHEAD_POS:
+ /* If lookahead RE is just colorset C, convert to AHEAD(C) */
+ if (s1 != NULL)
+ {
+ cloneouts(v->nfa, s1, lp, rp, AHEAD);
+ return;
+ }
+ break;
+ case LATYPE_AHEAD_NEG:
+ /* If lookahead RE is just colorset C, convert to AHEAD(^C)|$ */
+ if (s1 != NULL)
+ {
+ colorcomplement(v->nfa, v->cm, AHEAD, s1, lp, rp);
+ newarc(v->nfa, '$', 1, lp, rp);
+ newarc(v->nfa, '$', 0, lp, rp);
+ return;
+ }
+ break;
+ case LATYPE_BEHIND_POS:
+ /* If lookbehind RE is just colorset C, convert to BEHIND(C) */
+ if (s1 != NULL)
+ {
+ cloneouts(v->nfa, s1, lp, rp, BEHIND);
+ return;
+ }
+ break;
+ case LATYPE_BEHIND_NEG:
+ /* If lookbehind RE is just colorset C, convert to BEHIND(^C)|^ */
+ if (s1 != NULL)
+ {
+ colorcomplement(v->nfa, v->cm, BEHIND, s1, lp, rp);
+ newarc(v->nfa, '^', 1, lp, rp);
+ newarc(v->nfa, '^', 0, lp, rp);
+ return;
+ }
+ break;
+ default:
+ assert(NOTREACHED);
+ }
+
+ /* General case: we need a LACON subre and arc */
+ n = newlacon(v, begin, end, latype);
+ newarc(v->nfa, LACON, n, lp, rp);
+ }
+
+ /*
* subre - allocate a subre
*/
static struct subre *
*************** nfatree(struct vars * v,
*** 1826,1840 ****
if (t->right != NULL)
(DISCARD) nfatree(v, t->right, f);
! return nfanode(v, t, f);
}
/*
! * nfanode - do one NFA for nfatree
*/
static long /* optimize results */
nfanode(struct vars * v,
struct subre * t,
FILE *f) /* for debug output */
{
struct nfa *nfa;
--- 1902,1919 ----
if (t->right != NULL)
(DISCARD) nfatree(v, t->right, f);
! return nfanode(v, t, 0, f);
}
/*
! * nfanode - do one NFA for nfatree or lacons
! *
! * If converttosearch is true, apply makesearch() to the NFA.
*/
static long /* optimize results */
nfanode(struct vars * v,
struct subre * t,
+ int converttosearch,
FILE *f) /* for debug output */
{
struct nfa *nfa;
*************** nfanode(struct vars * v,
*** 1855,1864 ****
NOERRZ();
dupnfa(nfa, t->begin, t->end, nfa->init, nfa->final);
if (!ISERR())
- {
specialcolors(nfa);
ret = optimize(nfa, f);
! }
if (!ISERR())
compact(nfa, &t->cnfa);
--- 1934,1944 ----
NOERRZ();
dupnfa(nfa, t->begin, t->end, nfa->init, nfa->final);
if (!ISERR())
specialcolors(nfa);
+ if (!ISERR())
ret = optimize(nfa, f);
! if (converttosearch && !ISERR())
! makesearch(v, nfa);
if (!ISERR())
compact(nfa, &t->cnfa);
*************** nfanode(struct vars * v,
*** 1867,1879 ****
}
/*
! * newlacon - allocate a lookahead-constraint subRE
*/
static int /* lacon number */
newlacon(struct vars * v,
struct state * begin,
struct state * end,
! int pos)
{
int n;
struct subre *newlacons;
--- 1947,1959 ----
}
/*
! * newlacon - allocate a lookaround-constraint subRE
*/
static int /* lacon number */
newlacon(struct vars * v,
struct state * begin,
struct state * end,
! int latype)
{
int n;
struct subre *newlacons;
*************** newlacon(struct vars * v,
*** 1900,1912 ****
sub = &v->lacons[n];
sub->begin = begin;
sub->end = end;
! sub->subno = pos;
ZAPCNFA(sub->cnfa);
return n;
}
/*
! * freelacons - free lookahead-constraint subRE vector
*/
static void
freelacons(struct subre * subs,
--- 1980,1992 ----
sub = &v->lacons[n];
sub->begin = begin;
sub->end = end;
! sub->subno = latype;
ZAPCNFA(sub->cnfa);
return n;
}
/*
! * freelacons - free lookaround-constraint subRE vector
*/
static void
freelacons(struct subre * subs,
*************** dump(regex_t *re,
*** 2020,2028 ****
}
for (i = 1; i < g->nlacons; i++)
{
! fprintf(f, "\nla%d (%s):\n", i,
! (g->lacons[i].subno) ? "positive" : "negative");
! dumpcnfa(&g->lacons[i].cnfa, f);
}
fprintf(f, "\n");
dumpst(g->tree, f, 0);
--- 2100,2128 ----
}
for (i = 1; i < g->nlacons; i++)
{
! struct subre *lasub = &g->lacons[i];
! const char *latype;
!
! switch (lasub->subno)
! {
! case LATYPE_AHEAD_POS:
! latype = "positive lookahead";
! break;
! case LATYPE_AHEAD_NEG:
! latype = "negative lookahead";
! break;
! case LATYPE_BEHIND_POS:
! latype = "positive lookbehind";
! break;
! case LATYPE_BEHIND_NEG:
! latype = "negative lookbehind";
! break;
! default:
! latype = "???";
! break;
! }
! fprintf(f, "\nla%d (%s):\n", i, latype);
! dumpcnfa(&lasub->cnfa, f);
}
fprintf(f, "\n");
dumpst(g->tree, f, 0);
diff --git a/src/backend/regex/rege_dfa.c b/src/backend/regex/rege_dfa.c
index a37e4b0..7d90242 100644
*** a/src/backend/regex/rege_dfa.c
--- b/src/backend/regex/rege_dfa.c
*************** shortest(struct vars * v,
*** 287,292 ****
--- 287,416 ----
}
/*
+ * matchuntil - incremental matching engine
+ *
+ * This is meant for use with a search-style NFA (that is, the pattern is
+ * known to act as though it had a leading .*). We determine whether a
+ * match exists starting at v->start and ending at probe. Multiple calls
+ * require only O(N) time not O(N^2) so long as the probe values are
+ * nondecreasing. *lastcss and *lastcp must be initialized to NULL before
+ * starting a series of calls.
+ *
+ * Returns 1 if a match exists, 0 if not.
+ * Internal errors also return 0, with v->err set.
+ */
+ static int
+ matchuntil(struct vars * v,
+ struct dfa * d,
+ chr *probe, /* we want to know if a match ends here */
+ struct sset ** lastcss, /* state storage across calls */
+ chr **lastcp) /* state storage across calls */
+ {
+ chr *cp = *lastcp;
+ color co;
+ struct sset *css = *lastcss;
+ struct sset *ss;
+ struct colormap *cm = d->cm;
+
+ /* initialize and startup, or restart, if necessary */
+ if (cp == NULL || cp > probe)
+ {
+ cp = v->start;
+ css = initialize(v, d, cp);
+ if (css == NULL)
+ return 0;
+
+ FDEBUG((">>> startup >>>\n"));
+ co = d->cnfa->bos[(v->eflags & REG_NOTBOL) ? 0 : 1];
+ FDEBUG(("color %ld\n", (long) co));
+
+ css = miss(v, d, css, co, cp, v->start);
+ if (css == NULL)
+ return 0;
+ css->lastseen = cp;
+ }
+ else if (css == NULL)
+ {
+ /* we previously found that no match is possible beyond *lastcp */
+ return 0;
+ }
+ ss = css;
+
+ /*
+ * This is the main text-scanning loop. It seems worth having two copies
+ * to avoid the overhead of REG_FTRACE tests here, even in REG_DEBUG
+ * builds, when you're not actively tracing.
+ */
+ #ifdef REG_DEBUG
+ if (v->eflags & REG_FTRACE)
+ {
+ while (cp < probe)
+ {
+ FDEBUG((">>> at c%d >>>\n", (int) (css - d->ssets)));
+ co = GETCOLOR(cm, *cp);
+ FDEBUG(("char %c, color %ld\n", (char) *cp, (long) co));
+ ss = css->outs[co];
+ if (ss == NULL)
+ {
+ ss = miss(v, d, css, co, cp + 1, v->start);
+ if (ss == NULL)
+ break; /* NOTE BREAK OUT */
+ }
+ cp++;
+ ss->lastseen = cp;
+ css = ss;
+ }
+ }
+ else
+ #endif
+ {
+ while (cp < probe)
+ {
+ co = GETCOLOR(cm, *cp);
+ ss = css->outs[co];
+ if (ss == NULL)
+ {
+ ss = miss(v, d, css, co, cp + 1, v->start);
+ if (ss == NULL)
+ break; /* NOTE BREAK OUT */
+ }
+ cp++;
+ ss->lastseen = cp;
+ css = ss;
+ }
+ }
+
+ *lastcss = ss;
+ *lastcp = cp;
+
+ if (ss == NULL)
+ return 0; /* impossible match, or internal error */
+
+ /* We need to process one more chr, or the EOS symbol, to check match */
+ if (cp < v->stop)
+ {
+ FDEBUG((">>> at c%d >>>\n", (int) (css - d->ssets)));
+ co = GETCOLOR(cm, *cp);
+ FDEBUG(("char %c, color %ld\n", (char) *cp, (long) co));
+ ss = css->outs[co];
+ if (ss == NULL)
+ ss = miss(v, d, css, co, cp + 1, v->start);
+ }
+ else
+ {
+ assert(cp == v->stop);
+ co = d->cnfa->eos[(v->eflags & REG_NOTEOL) ? 0 : 1];
+ FDEBUG(("color %ld\n", (long) co));
+ ss = miss(v, d, css, co, cp, v->start);
+ }
+
+ if (ss == NULL || !(ss->flags & POSTSTATE))
+ return 0;
+
+ return 1;
+ }
+
+ /*
* lastcold - determine last point at which no progress had been made
*/
static chr * /* endpoint, or NULL */
*************** miss(struct vars * v,
*** 613,631 ****
}
/*
! * lacon - lookahead-constraint checker for miss()
*/
static int /* predicate: constraint satisfied? */
lacon(struct vars * v,
struct cnfa * pcnfa, /* parent cnfa */
chr *cp,
! pcolor co) /* "color" of the lookahead constraint */
{
int n;
struct subre *sub;
struct dfa *d;
- struct smalldfa sd;
chr *end;
/* Since this is recursive, it could be driven to stack overflow */
if (STACK_TOO_DEEP(v->re))
--- 737,755 ----
}
/*
! * lacon - lookaround-constraint checker for miss()
*/
static int /* predicate: constraint satisfied? */
lacon(struct vars * v,
struct cnfa * pcnfa, /* parent cnfa */
chr *cp,
! pcolor co) /* "color" of the lookaround constraint */
{
int n;
struct subre *sub;
struct dfa *d;
chr *end;
+ int satisfied;
/* Since this is recursive, it could be driven to stack overflow */
if (STACK_TOO_DEEP(v->re))
*************** lacon(struct vars * v,
*** 635,653 ****
}
n = co - pcnfa->ncolors;
! assert(n < v->g->nlacons && v->g->lacons != NULL);
FDEBUG(("=== testing lacon %d\n", n));
sub = &v->g->lacons[n];
! d = newdfa(v, &sub->cnfa, &v->g->cmap, &sd);
if (d == NULL)
- {
- ERR(REG_ESPACE);
return 0;
}
! end = longest(v, d, cp, v->stop, (int *) NULL);
! freedfa(d);
! FDEBUG(("=== lacon %d match %d\n", n, (end != NULL)));
! return (sub->subno) ? (end != NULL) : (end == NULL);
}
/*
--- 759,793 ----
}
n = co - pcnfa->ncolors;
! assert(n > 0 && n < v->g->nlacons && v->g->lacons != NULL);
FDEBUG(("=== testing lacon %d\n", n));
sub = &v->g->lacons[n];
! d = getladfa(v, n);
if (d == NULL)
return 0;
+ if (LATYPE_IS_AHEAD(sub->subno))
+ {
+ /* used to use longest() here, but shortest() could be much cheaper */
+ end = shortest(v, d, cp, cp, v->stop,
+ (chr **) NULL, (int *) NULL);
+ satisfied = LATYPE_IS_POS(sub->subno) ? (end != NULL) : (end == NULL);
}
! else
! {
! /*
! * To avoid doing O(N^2) work when repeatedly testing a lookbehind
! * constraint in an N-character string, we use matchuntil() which can
! * cache the DFA state across calls. We only need to restart if the
! * probe point decreases, which is not common. The NFA we're using is
! * a search NFA, so it doesn't mind scanning over stuff before the
! * nominal match.
! */
! satisfied = matchuntil(v, d, cp, &v->lblastcss[n], &v->lblastcp[n]);
! if (!LATYPE_IS_POS(sub->subno))
! satisfied = !satisfied;
! }
! FDEBUG(("=== lacon %d satisfied %d\n", n, satisfied));
! return satisfied;
}
/*
diff --git a/src/backend/regex/regexec.c b/src/backend/regex/regexec.c
index 8a21f2c..82659a0 100644
*** a/src/backend/regex/regexec.c
--- b/src/backend/regex/regexec.c
*************** struct vars
*** 112,118 ****
chr *search_start; /* search start of string */
chr *stop; /* just past end of string */
int err; /* error code if any (0 none) */
! struct dfa **subdfas; /* per-subre DFAs */
struct smalldfa dfa1;
struct smalldfa dfa2;
};
--- 112,121 ----
chr *search_start; /* search start of string */
chr *stop; /* just past end of string */
int err; /* error code if any (0 none) */
! struct dfa **subdfas; /* per-tree-subre DFAs */
! struct dfa **ladfas; /* per-lacon-subre DFAs */
! struct sset **lblastcss; /* per-lacon-subre lookbehind restart data */
! chr **lblastcp; /* per-lacon-subre lookbehind restart data */
struct smalldfa dfa1;
struct smalldfa dfa2;
};
*************** struct vars
*** 132,137 ****
--- 135,141 ----
*/
/* === regexec.c === */
static struct dfa *getsubdfa(struct vars *, struct subre *);
+ static struct dfa *getladfa(struct vars *, int);
static int find(struct vars *, struct cnfa *, struct colormap *);
static int cfind(struct vars *, struct cnfa *, struct colormap *);
static int cfindloop(struct vars *, struct cnfa *, struct colormap *, struct dfa *, struct dfa *, chr **);
*************** static int creviterdissect(struct vars *
*** 149,154 ****
--- 153,159 ----
/* === rege_dfa.c === */
static chr *longest(struct vars *, struct dfa *, chr *, chr *, int *);
static chr *shortest(struct vars *, struct dfa *, chr *, chr *, chr *, chr **, int *);
+ static int matchuntil(struct vars *, struct dfa *, chr *, struct sset **, chr **);
static chr *lastcold(struct vars *, struct dfa *);
static struct dfa *newdfa(struct vars *, struct cnfa *, struct colormap *, struct smalldfa *);
static void freedfa(struct dfa *);
*************** pg_regexec(regex_t *re,
*** 226,246 ****
v->search_start = (chr *) string + search_start;
v->stop = (chr *) string + len;
v->err = 0;
assert(v->g->ntree >= 0);
n = (size_t) v->g->ntree;
if (n <= LOCALDFAS)
v->subdfas = subdfas;
else
- v->subdfas = (struct dfa **) MALLOC(n * sizeof(struct dfa *));
- if (v->subdfas == NULL)
{
! if (v->pmatch != pmatch && v->pmatch != mat)
! FREE(v->pmatch);
! return REG_ESPACE;
}
for (i = 0; i < n; i++)
v->subdfas[i] = NULL;
/* do it */
assert(v->g->tree != NULL);
if (backref)
--- 231,284 ----
v->search_start = (chr *) string + search_start;
v->stop = (chr *) string + len;
v->err = 0;
+ v->subdfas = NULL;
+ v->ladfas = NULL;
+ v->lblastcss = NULL;
+ v->lblastcp = NULL;
+ /* below this point, "goto cleanup" will behave sanely */
+
assert(v->g->ntree >= 0);
n = (size_t) v->g->ntree;
if (n <= LOCALDFAS)
v->subdfas = subdfas;
else
{
! v->subdfas = (struct dfa **) MALLOC(n * sizeof(struct dfa *));
! if (v->subdfas == NULL)
! {
! st = REG_ESPACE;
! goto cleanup;
! }
}
for (i = 0; i < n; i++)
v->subdfas[i] = NULL;
+ assert(v->g->nlacons >= 0);
+ n = (size_t) v->g->nlacons;
+ if (n > 0)
+ {
+ v->ladfas = (struct dfa **) MALLOC(n * sizeof(struct dfa *));
+ if (v->ladfas == NULL)
+ {
+ st = REG_ESPACE;
+ goto cleanup;
+ }
+ for (i = 0; i < n; i++)
+ v->ladfas[i] = NULL;
+ v->lblastcss = (struct sset **) MALLOC(n * sizeof(struct sset *));
+ v->lblastcp = (chr **) MALLOC(n * sizeof(chr *));
+ if (v->lblastcss == NULL || v->lblastcp == NULL)
+ {
+ st = REG_ESPACE;
+ goto cleanup;
+ }
+ for (i = 0; i < n; i++)
+ {
+ v->lblastcss[i] = NULL;
+ v->lblastcp[i] = NULL;
+ }
+ }
+
/* do it */
assert(v->g->tree != NULL);
if (backref)
*************** pg_regexec(regex_t *re,
*** 257,278 ****
}
/* clean up */
if (v->pmatch != pmatch && v->pmatch != mat)
FREE(v->pmatch);
! n = (size_t) v->g->ntree;
! for (i = 0; i < n; i++)
{
! if (v->subdfas[i] != NULL)
! freedfa(v->subdfas[i]);
}
! if (v->subdfas != subdfas)
! FREE(v->subdfas);
return st;
}
/*
! * getsubdfa - create or re-fetch the DFA for a subre node
*
* We only need to create the DFA once per overall regex execution.
* The DFA will be freed by the cleanup step in pg_regexec().
--- 295,334 ----
}
/* clean up */
+ cleanup:
if (v->pmatch != pmatch && v->pmatch != mat)
FREE(v->pmatch);
! if (v->subdfas != NULL)
{
! n = (size_t) v->g->ntree;
! for (i = 0; i < n; i++)
! {
! if (v->subdfas[i] != NULL)
! freedfa(v->subdfas[i]);
! }
! if (v->subdfas != subdfas)
! FREE(v->subdfas);
}
! if (v->ladfas != NULL)
! {
! n = (size_t) v->g->nlacons;
! for (i = 0; i < n; i++)
! {
! if (v->ladfas[i] != NULL)
! freedfa(v->ladfas[i]);
! }
! FREE(v->ladfas);
! }
! if (v->lblastcss != NULL)
! FREE(v->lblastcss);
! if (v->lblastcp != NULL)
! FREE(v->lblastcp);
return st;
}
/*
! * getsubdfa - create or re-fetch the DFA for a tree subre node
*
* We only need to create the DFA once per overall regex execution.
* The DFA will be freed by the cleanup step in pg_regexec().
*************** getsubdfa(struct vars * v,
*** 291,296 ****
--- 347,374 ----
}
/*
+ * getladfa - create or re-fetch the DFA for a LACON subre node
+ *
+ * Same as above, but for LACONs.
+ */
+ static struct dfa *
+ getladfa(struct vars * v,
+ int n)
+ {
+ assert(n > 0 && n < v->g->nlacons && v->g->lacons != NULL);
+
+ if (v->ladfas[n] == NULL)
+ {
+ struct subre *sub = &v->g->lacons[n];
+
+ v->ladfas[n] = newdfa(v, &sub->cnfa, &v->g->cmap, DOMALLOC);
+ if (ISERR())
+ return NULL;
+ }
+ return v->ladfas[n];
+ }
+
+ /*
* find - find a match for the main NFA (no-complications case)
*/
static int
diff --git a/src/backend/regex/regexport.c b/src/backend/regex/regexport.c
index c5524ae..9134071 100644
*** a/src/backend/regex/regexport.c
--- b/src/backend/regex/regexport.c
***************
*** 6,12 ****
* In this implementation, the NFA defines a necessary but not sufficient
* condition for a string to match the regex: that is, there can be strings
* that match the NFA but don't match the full regex, but not vice versa.
! * Thus, for example, it is okay for the functions below to ignore lookahead
* constraints, which merely constrain the string some more.
*
* Notice that these functions return info into caller-provided arrays
--- 6,12 ----
* In this implementation, the NFA defines a necessary but not sufficient
* condition for a string to match the regex: that is, there can be strings
* that match the NFA but don't match the full regex, but not vice versa.
! * Thus, for example, it is okay for the functions below to ignore lookaround
* constraints, which merely constrain the string some more.
*
* Notice that these functions return info into caller-provided arrays
diff --git a/src/backend/regex/regprefix.c b/src/backend/regex/regprefix.c
index ce41620..8692845 100644
*** a/src/backend/regex/regprefix.c
--- b/src/backend/regex/regprefix.c
*************** static int findprefix(struct cnfa * cnfa
*** 36,42 ****
* the common prefix or exact value, of length *slength (measured in chrs
* not bytes!).
*
! * This function does not analyze all complex cases (such as lookahead
* constraints) exactly. Therefore it is possible that some strings matching
* the reported prefix or exact-match string do not satisfy the regex. But
* it should never be the case that a string satisfying the regex does not
--- 36,42 ----
* the common prefix or exact value, of length *slength (measured in chrs
* not bytes!).
*
! * This function does not analyze all complex cases (such as lookaround
* constraints) exactly. Therefore it is possible that some strings matching
* the reported prefix or exact-match string do not satisfy the regex. But
* it should never be the case that a string satisfying the regex does not
diff --git a/src/include/regex/regex.h b/src/include/regex/regex.h
index 5e1b692..2f89dc9 100644
*** a/src/include/regex/regex.h
--- b/src/include/regex/regex.h
*************** typedef struct
*** 58,64 ****
size_t re_nsub; /* number of subexpressions */
long re_info; /* information about RE */
#define REG_UBACKREF 000001
! #define REG_ULOOKAHEAD 000002
#define REG_UBOUNDS 000004
#define REG_UBRACES 000010
#define REG_UBSALNUM 000020
--- 58,64 ----
size_t re_nsub; /* number of subexpressions */
long re_info; /* information about RE */
#define REG_UBACKREF 000001
! #define REG_ULOOKAROUND 000002
#define REG_UBOUNDS 000004
#define REG_UBRACES 000010
#define REG_UBSALNUM 000020
diff --git a/src/include/regex/regguts.h b/src/include/regex/regguts.h
index 19fe991..2ceffa6 100644
*** a/src/include/regex/regguts.h
--- b/src/include/regex/regguts.h
***************
*** 89,101 ****
*/
#define NOTREACHED 0
- #define xxx 1
#define DUPMAX _POSIX2_RE_DUP_MAX
#define DUPINF (DUPMAX+1)
#define REMAGIC 0xfed7 /* magic number for main struct */
/*
--- 89,107 ----
*/
#define NOTREACHED 0
#define DUPMAX _POSIX2_RE_DUP_MAX
#define DUPINF (DUPMAX+1)
#define REMAGIC 0xfed7 /* magic number for main struct */
+ /* Type codes for lookaround constraints */
+ #define LATYPE_AHEAD_POS 03 /* positive lookahead */
+ #define LATYPE_AHEAD_NEG 02 /* negative lookahead */
+ #define LATYPE_BEHIND_POS 01 /* positive lookbehind */
+ #define LATYPE_BEHIND_NEG 00 /* negative lookbehind */
+ #define LATYPE_IS_POS(la) ((la) & 01)
+ #define LATYPE_IS_AHEAD(la) ((la) & 02)
/*
*************** struct nfa
*** 351,357 ****
*
* The non-dummy carc structs are of two types: plain arcs and LACON arcs.
* Plain arcs just store the transition color number as "co". LACON arcs
! * store the lookahead constraint number plus cnfa.ncolors as "co". LACON
* arcs can be distinguished from plain by testing for co >= cnfa.ncolors.
*/
struct carc
--- 357,363 ----
*
* The non-dummy carc structs are of two types: plain arcs and LACON arcs.
* Plain arcs just store the transition color number as "co". LACON arcs
! * store the lookaround constraint number plus cnfa.ncolors as "co". LACON
* arcs can be distinguished from plain by testing for co >= cnfa.ncolors.
*/
struct carc
*************** struct cnfa
*** 365,371 ****
int nstates; /* number of states */
int ncolors; /* number of colors (max color in use + 1) */
int flags;
! #define HASLACONS 01 /* uses lookahead constraints */
int pre; /* setup state number */
int post; /* teardown state number */
color bos[2]; /* colors, if any, assigned to BOS and BOL */
--- 371,377 ----
int nstates; /* number of states */
int ncolors; /* number of colors (max color in use + 1) */
int flags;
! #define HASLACONS 01 /* uses lookaround constraints */
int pre; /* setup state number */
int post; /* teardown state number */
color bos[2]; /* colors, if any, assigned to BOS and BOL */
*************** struct subre
*** 433,439 ****
#define PREF2(f1, f2) ((PREF(f1) != 0) ? PREF(f1) : PREF(f2))
#define COMBINE(f1, f2) (UP((f1)|(f2)) | PREF2(f1, f2))
short id; /* ID of subre (1..ntree-1) */
! int subno; /* subexpression number (for 'b' and '(') */
short min; /* min repetitions for iteration or backref */
short max; /* max repetitions for iteration or backref */
struct subre *left; /* left child, if any (also freelist chain) */
--- 439,446 ----
#define PREF2(f1, f2) ((PREF(f1) != 0) ? PREF(f1) : PREF(f2))
#define COMBINE(f1, f2) (UP((f1)|(f2)) | PREF2(f1, f2))
short id; /* ID of subre (1..ntree-1) */
! int subno; /* subexpression number for 'b' and '(', or
! * LATYPE code for lookaround constraint */
short min; /* min repetitions for iteration or backref */
short max; /* max repetitions for iteration or backref */
struct subre *left; /* left child, if any (also freelist chain) */
*************** struct guts
*** 479,484 ****
int ntree; /* number of subre's, plus one */
struct colormap cmap;
int FUNCPTR(compare, (const chr *, const chr *, size_t));
! struct subre *lacons; /* lookahead-constraint vector */
! int nlacons; /* size of lacons */
};
--- 486,492 ----
int ntree; /* number of subre's, plus one */
struct colormap cmap;
int FUNCPTR(compare, (const chr *, const chr *, size_t));
! struct subre *lacons; /* lookaround-constraint vector */
! int nlacons; /* size of lacons[]; note that only slots
! * numbered 1 .. nlacons-1 are used */
};
diff --git a/src/test/regress/expected/regex.out b/src/test/regress/expected/regex.out
index be15185..f0e2fc9 100644
*** a/src/test/regress/expected/regex.out
--- b/src/test/regress/expected/regex.out
*************** select substring('a' from '((a)+)');
*** 90,95 ****
--- 90,264 ----
a
(1 row)
+ -- Test lookahead constraints
+ select regexp_matches('ab', 'a(?=b)b*');
+ regexp_matches
+ ----------------
+ {ab}
+ (1 row)
+
+ select regexp_matches('a', 'a(?=b)b*');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ select regexp_matches('abc', 'a(?=b)b*(?=c)c*');
+ regexp_matches
+ ----------------
+ {abc}
+ (1 row)
+
+ select regexp_matches('ab', 'a(?=b)b*(?=c)c*');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ select regexp_matches('ab', 'a(?!b)b*');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ select regexp_matches('a', 'a(?!b)b*');
+ regexp_matches
+ ----------------
+ {a}
+ (1 row)
+
+ select regexp_matches('b', '(?=b)b');
+ regexp_matches
+ ----------------
+ {b}
+ (1 row)
+
+ select regexp_matches('a', '(?=b)b');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ -- Test lookbehind constraints
+ select regexp_matches('abb', '(?<=a)b*');
+ regexp_matches
+ ----------------
+ {bb}
+ (1 row)
+
+ select regexp_matches('a', 'a(?<=a)b*');
+ regexp_matches
+ ----------------
+ {a}
+ (1 row)
+
+ select regexp_matches('abc', 'a(?<=a)b*(?<=b)c*');
+ regexp_matches
+ ----------------
+ {abc}
+ (1 row)
+
+ select regexp_matches('ab', 'a(?<=a)b*(?<=b)c*');
+ regexp_matches
+ ----------------
+ {ab}
+ (1 row)
+
+ select regexp_matches('ab', 'a*(?<!a)b*');
+ regexp_matches
+ ----------------
+ {""}
+ (1 row)
+
+ select regexp_matches('ab', 'a*(?<!a)b+');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ select regexp_matches('b', 'a*(?<!a)b+');
+ regexp_matches
+ ----------------
+ {b}
+ (1 row)
+
+ select regexp_matches('a', 'a(?<!a)b*');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ select regexp_matches('b', '(?<=b)b');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ select regexp_matches('foobar', '(?<=f)b+');
+ regexp_matches
+ ----------------
+ (0 rows)
+
+ select regexp_matches('foobar', '(?<=foo)b+');
+ regexp_matches
+ ----------------
+ {b}
+ (1 row)
+
+ select regexp_matches('foobar', '(?<=oo)b+');
+ regexp_matches
+ ----------------
+ {b}
+ (1 row)
+
+ -- Test optimization of single-chr-or-bracket-expression lookaround constraints
+ select 'xz' ~ 'x(?=[xy])';
+ ?column?
+ ----------
+ f
+ (1 row)
+
+ select 'xy' ~ 'x(?=[xy])';
+ ?column?
+ ----------
+ t
+ (1 row)
+
+ select 'xz' ~ 'x(?![xy])';
+ ?column?
+ ----------
+ t
+ (1 row)
+
+ select 'xy' ~ 'x(?![xy])';
+ ?column?
+ ----------
+ f
+ (1 row)
+
+ select 'x' ~ 'x(?![xy])';
+ ?column?
+ ----------
+ t
+ (1 row)
+
+ select 'xyy' ~ '(?<=[xy])yy+';
+ ?column?
+ ----------
+ t
+ (1 row)
+
+ select 'zyy' ~ '(?<=[xy])yy+';
+ ?column?
+ ----------
+ f
+ (1 row)
+
+ select 'xyy' ~ '(?<![xy])yy+';
+ ?column?
+ ----------
+ f
+ (1 row)
+
+ select 'zyy' ~ '(?<![xy])yy+';
+ ?column?
+ ----------
+ t
+ (1 row)
+
-- Test conversion of regex patterns to indexable conditions
explain (costs off) select * from pg_proc where proname ~ 'abc';
QUERY PLAN
diff --git a/src/test/regress/sql/regex.sql b/src/test/regress/sql/regex.sql
index c59fa35..d3030af 100644
*** a/src/test/regress/sql/regex.sql
--- b/src/test/regress/sql/regex.sql
*************** select substring('asd TO foo' from ' TO
*** 25,30 ****
--- 25,65 ----
select substring('a' from '((a))+');
select substring('a' from '((a)+)');
+ -- Test lookahead constraints
+ select regexp_matches('ab', 'a(?=b)b*');
+ select regexp_matches('a', 'a(?=b)b*');
+ select regexp_matches('abc', 'a(?=b)b*(?=c)c*');
+ select regexp_matches('ab', 'a(?=b)b*(?=c)c*');
+ select regexp_matches('ab', 'a(?!b)b*');
+ select regexp_matches('a', 'a(?!b)b*');
+ select regexp_matches('b', '(?=b)b');
+ select regexp_matches('a', '(?=b)b');
+
+ -- Test lookbehind constraints
+ select regexp_matches('abb', '(?<=a)b*');
+ select regexp_matches('a', 'a(?<=a)b*');
+ select regexp_matches('abc', 'a(?<=a)b*(?<=b)c*');
+ select regexp_matches('ab', 'a(?<=a)b*(?<=b)c*');
+ select regexp_matches('ab', 'a*(?<!a)b*');
+ select regexp_matches('ab', 'a*(?<!a)b+');
+ select regexp_matches('b', 'a*(?<!a)b+');
+ select regexp_matches('a', 'a(?<!a)b*');
+ select regexp_matches('b', '(?<=b)b');
+ select regexp_matches('foobar', '(?<=f)b+');
+ select regexp_matches('foobar', '(?<=foo)b+');
+ select regexp_matches('foobar', '(?<=oo)b+');
+
+ -- Test optimization of single-chr-or-bracket-expression lookaround constraints
+ select 'xz' ~ 'x(?=[xy])';
+ select 'xy' ~ 'x(?=[xy])';
+ select 'xz' ~ 'x(?![xy])';
+ select 'xy' ~ 'x(?![xy])';
+ select 'x' ~ 'x(?![xy])';
+ select 'xyy' ~ '(?<=[xy])yy+';
+ select 'zyy' ~ '(?<=[xy])yy+';
+ select 'xyy' ~ '(?<![xy])yy+';
+ select 'zyy' ~ '(?<![xy])yy+';
+
-- Test conversion of regex patterns to indexable conditions
explain (costs off) select * from pg_proc where proname ~ 'abc';
explain (costs off) select * from pg_proc where proname ~ '^abc';
pgsql-hackers by date: