401 lines
8.0 KiB
C
401 lines
8.0 KiB
C
/*
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* Copyright (c) 1980 Regents of the University of California.
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* All rights reserved. The Berkeley software License Agreement
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* specifies the terms and conditions for redistribution.
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*/
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/*
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* routines to do regular expression matching
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*
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* Entry points:
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*
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* re_comp(s)
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* char *s;
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* ... returns 0 if the string s was compiled successfully,
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* a pointer to an error message otherwise.
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* If passed 0 or a null string returns without changing
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* the currently compiled re (see note 11 below).
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*
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* re_exec(s)
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* char *s;
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* ... returns 1 if the string s matches the last compiled regular
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* expression,
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* 0 if the string s failed to match the last compiled
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* regular expression, and
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* -1 if the compiled regular expression was invalid
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* (indicating an internal error).
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*
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* The strings passed to both re_comp and re_exec may have trailing or
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* embedded newline characters; they are terminated by nulls.
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*
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* The identity of the author of these routines is lost in antiquity;
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* this is essentially the same as the re code in the original V6 ed.
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*
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* The regular expressions recognized are described below. This description
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* is essentially the same as that for ed.
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*
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* A regular expression specifies a set of strings of characters.
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* A member of this set of strings is said to be matched by
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* the regular expression. In the following specification for
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* regular expressions the word `character' means any character but NUL.
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*
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* 1. Any character except a special character matches itself.
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* Special characters are the regular expression delimiter plus
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* \ [ . and sometimes ^ * $.
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* 2. A . matches any character.
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* 3. A \ followed by any character except a digit or ( )
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* matches that character.
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* 4. A nonempty string s bracketed [s] (or [^s]) matches any
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* character in (or not in) s. In s, \ has no special meaning,
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* and ] may only appear as the first letter. A substring
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* a-b, with a and b in ascending ASCII order, stands for
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* the inclusive range of ASCII characters.
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* 5. A regular expression of form 1-4 followed by * matches a
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* sequence of 0 or more matches of the regular expression.
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* 6. A regular expression, x, of form 1-8, bracketed \(x\)
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* matches what x matches.
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* 7. A \ followed by a digit n matches a copy of the string that the
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* bracketed regular expression beginning with the nth \( matched.
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* 8. A regular expression of form 1-8, x, followed by a regular
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* expression of form 1-7, y matches a match for x followed by
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* a match for y, with the x match being as long as possible
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* while still permitting a y match.
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* 9. A regular expression of form 1-8 preceded by ^ (or followed
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* by $), is constrained to matches that begin at the left
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* (or end at the right) end of a line.
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* 10. A regular expression of form 1-9 picks out the longest among
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* the leftmost matches in a line.
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* 11. An empty regular expression stands for a copy of the last
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* regular expression encountered.
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*/
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/*
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* constants for re's
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*/
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#define CBRA 1
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#define CCHR 2
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#define CDOT 4
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#define CCL 6
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#define NCCL 8
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#define CDOL 10
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#define CEOF 11
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#define CKET 12
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#define CBACK 18
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#define CSTAR 01
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#define ESIZE 512
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#define NBRA 9
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static char expbuf[ESIZE], *braslist[NBRA], *braelist[NBRA];
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static char circf;
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/*
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* compile the regular expression argument into a dfa
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*/
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char *
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re_comp(sp)
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register char *sp;
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{
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register int c;
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register char *ep = expbuf;
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int cclcnt, numbra = 0;
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char *lastep = 0;
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char bracket[NBRA];
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char *bracketp = &bracket[0];
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static char *retoolong = "Regular expression too long";
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#define comerr(msg) {expbuf[0] = 0; numbra = 0; return(msg); }
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if (sp == 0 || *sp == '\0') {
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if (*ep == 0)
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return("No previous regular expression");
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return(0);
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}
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if (*sp == '^') {
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circf = 1;
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sp++;
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}
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else
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circf = 0;
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for (;;) {
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if (ep >= &expbuf[ESIZE])
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comerr(retoolong);
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if ((c = *sp++) == '\0') {
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if (bracketp != bracket)
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comerr("unmatched \\(");
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*ep++ = CEOF;
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*ep++ = 0;
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return(0);
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}
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if (c != '*')
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lastep = ep;
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switch (c) {
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case '.':
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*ep++ = CDOT;
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continue;
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case '*':
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if (lastep == 0 || *lastep == CBRA || *lastep == CKET)
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goto defchar;
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*lastep |= CSTAR;
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continue;
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case '$':
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if (*sp != '\0')
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goto defchar;
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*ep++ = CDOL;
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continue;
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case '[':
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*ep++ = CCL;
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*ep++ = 0;
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cclcnt = 1;
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if ((c = *sp++) == '^') {
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c = *sp++;
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ep[-2] = NCCL;
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}
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do {
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if (c == '\0')
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comerr("missing ]");
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if (c == '-' && ep [-1] != 0) {
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if ((c = *sp++) == ']') {
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*ep++ = '-';
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cclcnt++;
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break;
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}
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while (ep[-1] < c) {
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*ep = ep[-1] + 1;
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ep++;
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cclcnt++;
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if (ep >= &expbuf[ESIZE])
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comerr(retoolong);
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}
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}
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*ep++ = c;
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cclcnt++;
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if (ep >= &expbuf[ESIZE])
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comerr(retoolong);
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} while ((c = *sp++) != ']');
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lastep[1] = cclcnt;
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continue;
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case '\\':
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if ((c = *sp++) == '(') {
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if (numbra >= NBRA)
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comerr("too many \\(\\) pairs");
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*bracketp++ = numbra;
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*ep++ = CBRA;
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*ep++ = numbra++;
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continue;
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}
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if (c == ')') {
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if (bracketp <= bracket)
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comerr("unmatched \\)");
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*ep++ = CKET;
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*ep++ = *--bracketp;
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continue;
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}
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if (c >= '1' && c < ('1' + NBRA)) {
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*ep++ = CBACK;
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*ep++ = c - '1';
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continue;
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}
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*ep++ = CCHR;
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*ep++ = c;
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continue;
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defchar:
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default:
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*ep++ = CCHR;
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*ep++ = c;
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}
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}
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}
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static int
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cclass(set, c, af)
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register char *set, c;
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int af;
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{
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register int n;
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if (c == 0)
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return(0);
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n = *set++;
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while (--n)
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if (*set++ == c)
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return(af);
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return(! af);
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}
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static int
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backref(i, lp)
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register int i;
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register char *lp;
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{
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register char *bp;
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bp = braslist[i];
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while (*bp++ == *lp++)
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if (bp >= braelist[i])
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return(1);
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return(0);
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}
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/*
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* try to match the next thing in the dfa
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*/
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static int
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advance(lp, ep)
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register char *lp, *ep;
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{
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register char *curlp;
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int ct, i;
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int rv;
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for (;;)
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switch (*ep++) {
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case CCHR:
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if (*ep++ == *lp++)
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continue;
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return(0);
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case CDOT:
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if (*lp++)
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continue;
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return(0);
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case CDOL:
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if (*lp == '\0')
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continue;
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return(0);
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case CEOF:
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return(1);
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case CCL:
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if (cclass(ep, *lp++, 1)) {
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ep += *ep;
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continue;
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}
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return(0);
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case NCCL:
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if (cclass(ep, *lp++, 0)) {
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ep += *ep;
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continue;
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}
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return(0);
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case CBRA:
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braslist[(unsigned char)*ep++] = lp;
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continue;
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case CKET:
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braelist[(unsigned char)*ep++] = lp;
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continue;
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case CBACK:
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if (braelist[i = *ep++] == 0)
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return(-1);
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if (backref(i, lp)) {
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lp += braelist[i] - braslist[i];
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continue;
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}
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return(0);
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case CBACK|CSTAR:
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if (braelist[i = *ep++] == 0)
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return(-1);
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curlp = lp;
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ct = braelist[i] - braslist[i];
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while (backref(i, lp))
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lp += ct;
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while (lp >= curlp) {
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rv = advance(lp, ep);
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if (rv)
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return(rv);
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lp -= ct;
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}
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continue;
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case CDOT|CSTAR:
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curlp = lp;
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while (*lp++)
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;
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goto star;
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case CCHR|CSTAR:
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curlp = lp;
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while (*lp++ == *ep)
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;
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ep++;
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goto star;
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case CCL|CSTAR:
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case NCCL|CSTAR:
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curlp = lp;
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while (cclass(ep, *lp++, ep[-1] == (CCL|CSTAR)))
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;
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ep += *ep;
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goto star;
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star:
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do {
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lp--;
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rv = advance(lp, ep);
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if (rv)
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return(rv);
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} while (lp > curlp);
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return(0);
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default:
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return(-1);
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}
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}
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/*
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* match the argument string against the compiled re
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*/
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int
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re_exec(p1)
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register char *p1;
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{
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register char *p2 = expbuf;
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register int c;
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int rv;
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for (c = 0; c < NBRA; c++) {
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braslist[c] = 0;
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braelist[c] = 0;
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}
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if (circf)
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return((advance(p1, p2)));
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/*
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* fast check for first character
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*/
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if (*p2 == CCHR) {
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c = p2[1];
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do {
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if (*p1 != c)
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continue;
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rv = advance(p1, p2);
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if (rv)
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return(rv);
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} while (*p1++);
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return(0);
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}
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/*
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* regular algorithm
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*/
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do {
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rv = advance(p1, p2);
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if (rv)
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return(rv);
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} while (*p1++);
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return(0);
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}
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