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12c9a04008
A lookbehind constraint is like a lookahead constraint in that it consumes no text; but it checks for existence (or nonexistence) of a match *ending* at the current point in the string, rather than one *starting* at the current point. This is a long-requested feature since it exists in many other regex libraries, but Henry Spencer had never got around to implementing it in the code we use. Just making it work is actually pretty trivial; but naive copying of the logic for lookahead constraints leads to code that often spends O(N^2) time to scan an N-character string, because we have to run the match engine from string start to the current probe point each time the constraint is checked. In typical use-cases a lookbehind constraint will be written at the start of the regex and hence will need to be checked at every character --- so O(N^2) work overall. To fix that, I introduced a third copy of the core DFA matching loop, paralleling the existing longest() and shortest() loops. This version, matchuntil(), can suspend and resume matching given a couple of pointers' worth of storage space. So we need only run it across the string once, stopping at each interesting probe point and then resuming to advance to the next one. I also put in an optimization that simplifies one-character lookahead and lookbehind constraints, such as "(?=x)" or "(?<!\w)", into AHEAD and BEHIND constraints, which already existed in the engine. This avoids the overhead of the LACON machinery entirely for these rather common cases. The net result is that lookbehind constraints run a factor of three or so slower than Perl's for multi-character constraints, but faster than Perl's for one-character constraints ... and they work fine for variable-length constraints, which Perl gives up on entirely. So that's not bad from a competitive perspective, and there's room for further optimization if anyone cares. (In reality, raw scan rate across a large input string is probably not that big a deal for Postgres usage anyway; so I'm happy if it's linear.)
178 lines
6.5 KiB
C
178 lines
6.5 KiB
C
#ifndef _REGEX_H_
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#define _REGEX_H_ /* never again */
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/*
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* regular expressions
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*
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* Copyright (c) 1998, 1999 Henry Spencer. All rights reserved.
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*
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* Development of this software was funded, in part, by Cray Research Inc.,
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* UUNET Communications Services Inc., Sun Microsystems Inc., and Scriptics
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* Corporation, none of whom are responsible for the results. The author
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* thanks all of them.
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*
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* Redistribution and use in source and binary forms -- with or without
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* modification -- are permitted for any purpose, provided that
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* redistributions in source form retain this entire copyright notice and
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* indicate the origin and nature of any modifications.
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*
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* I'd appreciate being given credit for this package in the documentation
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* of software which uses it, but that is not a requirement.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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* AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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* HENRY SPENCER BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* src/include/regex/regex.h
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*/
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/*
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* Add your own defines, if needed, here.
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*/
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#include "mb/pg_wchar.h"
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/*
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* interface types etc.
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*/
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/*
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* regoff_t has to be large enough to hold either off_t or ssize_t,
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* and must be signed; it's only a guess that long is suitable.
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*/
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typedef long regoff_t;
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/*
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* other interface types
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*/
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/* the biggie, a compiled RE (or rather, a front end to same) */
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typedef struct
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{
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int re_magic; /* magic number */
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size_t re_nsub; /* number of subexpressions */
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long re_info; /* information about RE */
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#define REG_UBACKREF 000001
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#define REG_ULOOKAROUND 000002
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#define REG_UBOUNDS 000004
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#define REG_UBRACES 000010
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#define REG_UBSALNUM 000020
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#define REG_UPBOTCH 000040
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#define REG_UBBS 000100
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#define REG_UNONPOSIX 000200
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#define REG_UUNSPEC 000400
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#define REG_UUNPORT 001000
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#define REG_ULOCALE 002000
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#define REG_UEMPTYMATCH 004000
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#define REG_UIMPOSSIBLE 010000
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#define REG_USHORTEST 020000
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int re_csize; /* sizeof(character) */
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char *re_endp; /* backward compatibility kludge */
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Oid re_collation; /* Collation that defines LC_CTYPE behavior */
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/* the rest is opaque pointers to hidden innards */
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char *re_guts; /* `char *' is more portable than `void *' */
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char *re_fns;
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} regex_t;
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/* result reporting (may acquire more fields later) */
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typedef struct
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{
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regoff_t rm_so; /* start of substring */
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regoff_t rm_eo; /* end of substring */
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} regmatch_t;
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/* supplementary control and reporting */
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typedef struct
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{
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regmatch_t rm_extend; /* see REG_EXPECT */
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} rm_detail_t;
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/*
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* regex compilation flags
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*/
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#define REG_BASIC 000000 /* BREs (convenience) */
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#define REG_EXTENDED 000001 /* EREs */
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#define REG_ADVF 000002 /* advanced features in EREs */
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#define REG_ADVANCED 000003 /* AREs (which are also EREs) */
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#define REG_QUOTE 000004 /* no special characters, none */
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#define REG_NOSPEC REG_QUOTE /* historical synonym */
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#define REG_ICASE 000010 /* ignore case */
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#define REG_NOSUB 000020 /* don't care about subexpressions */
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#define REG_EXPANDED 000040 /* expanded format, white space & comments */
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#define REG_NLSTOP 000100 /* \n doesn't match . or [^ ] */
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#define REG_NLANCH 000200 /* ^ matches after \n, $ before */
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#define REG_NEWLINE 000300 /* newlines are line terminators */
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#define REG_PEND 000400 /* ugh -- backward-compatibility hack */
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#define REG_EXPECT 001000 /* report details on partial/limited matches */
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#define REG_BOSONLY 002000 /* temporary kludge for BOS-only matches */
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#define REG_DUMP 004000 /* none of your business :-) */
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#define REG_FAKE 010000 /* none of your business :-) */
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#define REG_PROGRESS 020000 /* none of your business :-) */
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/*
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* regex execution flags
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*/
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#define REG_NOTBOL 0001 /* BOS is not BOL */
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#define REG_NOTEOL 0002 /* EOS is not EOL */
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#define REG_STARTEND 0004 /* backward compatibility kludge */
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#define REG_FTRACE 0010 /* none of your business */
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#define REG_MTRACE 0020 /* none of your business */
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#define REG_SMALL 0040 /* none of your business */
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/*
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* error reporting
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* Be careful if modifying the list of error codes -- the table used by
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* regerror() is generated automatically from this file!
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*/
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#define REG_OKAY 0 /* no errors detected */
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#define REG_NOMATCH 1 /* failed to match */
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#define REG_BADPAT 2 /* invalid regexp */
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#define REG_ECOLLATE 3 /* invalid collating element */
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#define REG_ECTYPE 4 /* invalid character class */
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#define REG_EESCAPE 5 /* invalid escape \ sequence */
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#define REG_ESUBREG 6 /* invalid backreference number */
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#define REG_EBRACK 7 /* brackets [] not balanced */
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#define REG_EPAREN 8 /* parentheses () not balanced */
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#define REG_EBRACE 9 /* braces {} not balanced */
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#define REG_BADBR 10 /* invalid repetition count(s) */
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#define REG_ERANGE 11 /* invalid character range */
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#define REG_ESPACE 12 /* out of memory */
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#define REG_BADRPT 13 /* quantifier operand invalid */
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#define REG_ASSERT 15 /* "can't happen" -- you found a bug */
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#define REG_INVARG 16 /* invalid argument to regex function */
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#define REG_MIXED 17 /* character widths of regex and string differ */
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#define REG_BADOPT 18 /* invalid embedded option */
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#define REG_ETOOBIG 19 /* regular expression is too complex */
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#define REG_ECOLORS 20 /* too many colors */
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#define REG_CANCEL 21 /* operation cancelled */
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/* two specials for debugging and testing */
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#define REG_ATOI 101 /* convert error-code name to number */
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#define REG_ITOA 102 /* convert error-code number to name */
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/* non-error result codes for pg_regprefix */
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#define REG_PREFIX (-1) /* identified a common prefix */
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#define REG_EXACT (-2) /* identified an exact match */
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/*
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* the prototypes for exported functions
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*/
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extern int pg_regcomp(regex_t *, const pg_wchar *, size_t, int, Oid);
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extern int pg_regexec(regex_t *, const pg_wchar *, size_t, size_t, rm_detail_t *, size_t, regmatch_t[], int);
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extern int pg_regprefix(regex_t *, pg_wchar **, size_t *);
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extern void pg_regfree(regex_t *);
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extern size_t pg_regerror(int, const regex_t *, char *, size_t);
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extern void pg_set_regex_collation(Oid collation);
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#endif /* _REGEX_H_ */
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