regexp.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

		     * parentheses already has. 
		     */
		    if (regstartp[no] == (char *)NULL)
			regstartp[no] = save;
		    return (1);
		} else
		    return (0);
	    }
	    break;
	case CLOSE + 1:
	case CLOSE + 2:
	case CLOSE + 3:
	case CLOSE + 4:
	case CLOSE + 5:
	case CLOSE + 6:
	case CLOSE + 7:
	case CLOSE + 8:
	case CLOSE + 9:{
		register int    no;
		register char  *save;

		no = OP(scan) - CLOSE;
		save = reginput;

		if (regmatch(nxt)) {
		    /*
		     * Don't set endp if some later invocation of the same
		     * parentheses already has. 
		     */
		    if (regendp[no] == (char *)NULL)
			regendp[no] = save;
		    return (1);
		} else
		    return (0);
	    }
	    break;
	case BRANCH:{
		register char  *save;

		if (OP(nxt) != BRANCH)	/* No choice. */
		    nxt = OPERAND(scan);	/* Avoid recursion. */
		else {
		    do {
			save = reginput;
			if (regmatch(OPERAND(scan)))
			    return (1);
			reginput = save;
			scan = regnext(scan);
		    } while (scan != (char *)NULL && OP(scan) == BRANCH);
		    return (0);
		    /* NOTREACHED */
		}
	    }
	    break;
	case STAR:{
		register char   nextch;
		register int    no;
		register char  *save;
		register int    minimum;

		/*
		 * Lookahead to avoid useless match attempts when we know
		 * what character comes next. 
		 */
		nextch = '\0';
		if (OP(nxt) == EXACTLY)
		    nextch = *OPERAND(nxt);
		minimum = (OP(scan) == STAR) ? 0 : 1;
		save = reginput;
		no = regrepeat(OPERAND(scan));
		while (no >= minimum) {
		    /* If it could work, try it. */
		    if (nextch == '\0' || *reginput == nextch)
			if (regmatch(nxt))
			    return (1);
		    /* Couldn't or didn't -- back up. */
		    no--;
		    reginput = save + no;
		}
		return (0);
	    }
	    break;
	case END:
	    return (1);		/* Success! */
	    break;
	default:
	    regerror("memory corruption");
	    return (0);
	    break;
	}

	scan = nxt;
    }

    /*
     * We get here only if there's trouble -- normally "case END" is the
     * terminating point. 
     */
    regerror("corrupted pointers");
    return (0);
}

/*
 - regrepeat - repeatedly match something simple, report how many
 */
#ifdef __STDC__

static int regrepeat(char *p)

#else

static int regrepeat(p)
char           *p;

#endif
{
    register int    count = 0;
    register char  *scan;
    register char  *opnd;

    scan = reginput;
    opnd = OPERAND(p);
    switch (OP(p)) {
    case ANY:
	count = strlen(scan);
	scan += count;
	break;
    case EXACTLY:
	while (*opnd == *scan) {
	    count++;
	    scan++;
	}
	break;
    case ANYOF:
	while (*scan != '\0' && strchr(opnd, *scan) != (char *)NULL) {
	    count++;
	    scan++;
	}
	break;
    case ANYBUT:
	while (*scan != '\0' && strchr(opnd, *scan) == (char *)NULL) {
	    count++;
	    scan++;
	}
	break;
    default:			/* Oh dear.  Called inappropriately. */
	regerror("internal foulup");
	count = 0;		/* Best compromise. */
	break;
    }
    reginput = scan;

    return (count);
}


/*
 - regnext - dig the "nxt" pointer out of a node
 */
#ifdef __STDC__

static char *regnext(register char *p)

#else

static char *regnext(p)
register char  *p;

#endif
{
    register int    offset;

    if (p == &regdummy)
	return ((char *)NULL);

    offset = NEXT(p);
    if (offset == 0)
	return ((char *)NULL);

    if (OP(p) == BACK)
	return (p - offset);
    else
	return (p + offset);
}

#ifdef DEBUG

STATIC char    *regprop();

/*
 - regdump - dump a regexp onto stdout in vaguely comprehensible form
 */
#ifdef __STDC__

void regdump(regexp *r)

#else

void regdump(r)
regexp         *r;

#endif
{
    register char  *s;
    register char   op = EXACTLY;	/* Arbitrary non-END op. */
    register char  *nxt;
    extern char    *strchr();


    s = r->program + 1;
    while (op != END) {		/* While that wasn't END last time... */
	op = OP(s);
	printf("%2d%s", s - r->program, regprop(s));	/* Where, what. */
	nxt = regnext(s);
	if (nxt == (char *)NULL)	/* nxt ptr. */
	    printf("(0)");
	else
	    printf("(%d)", (s - r->program) + (nxt - s));
	s += 3;
	if (op == ANYOF || op == ANYBUT || op == EXACTLY) {
	    /* Literal string, where present. */
	    while (*s != '\0') {
		putchar(*s);
		s++;
	    }
	    s++;
	}
	putchar('\n');
    }

    /* Header fields of interest. */
    if (r->regstart != '\0')
	printf("start `%c' ", r->regstart);
    if (r->reganch)
	printf("anchored ");
    if (r->regmust != (char *)NULL)
	printf("must have \"%s\"", r->regmust);
    printf("\n");
}

/*
 - regprop - printable representation of opcode
 */
#ifdef __STDC__

static char *regprop(char *op)

#else

static char *regprop(op)
char           *op;

#endif
{
    register char  *p;
    static char     buf[50];

    strcpy(buf, ":");

    switch (OP(op)) {
    case BOL:
	p = "BOL";
	break;
    case EOL:
	p = "EOL";
	break;
    case ANY:
	p = "ANY";
	break;
    case ANYOF:
	p = "ANYOF";
	break;
    case ANYBUT:
	p = "ANYBUT";
	break;
    case BRANCH:
	p = "BRANCH";
	break;
    case EXACTLY:
	p = "EXACTLY";
	break;
    case NOTHING:
	p = "NOTHING";
	break;
    case BACK:
	p = "BACK";
	break;
    case END:
	p = "END";
	break;
    case OPEN + 1:
    case OPEN + 2:
    case OPEN + 3:
    case OPEN + 4:
    case OPEN + 5:
    case OPEN + 6:
    case OPEN + 7:
    case OPEN + 8:
    case OPEN + 9:
	sprintf(buf + strlen(buf), "OPEN%d", OP(op) - OPEN);
	p = (char *)NULL;
	break;
    case CLOSE + 1:
    case CLOSE + 2:
    case CLOSE + 3:
    case CLOSE + 4:
    case CLOSE + 5:
    case CLOSE + 6:
    case CLOSE + 7:
    case CLOSE + 8:
    case CLOSE + 9:
	sprintf(buf + strlen(buf), "CLOSE%d", OP(op) - CLOSE);
	p = (char *)NULL;
	break;
    case STAR:
	p = "STAR";
	break;
    default:
	regerror("corrupted opcode");
	break;
    }
    if (p != (char *)NULL)
	strcat(buf, p);
    return (buf);
}
#endif

/*
 * The following is provided for those people who do not have strcspn() in
 * their C libraries.  They should get off their butts and do something
 * about it; at least one public-domain implementation of those (highly
 * useful) string routines has been published on Usenet.
 */
#ifdef STRCSPN
/*
 * strcspn - find length of initial segment of s1 consisting entirely
 * of characters not from s2
 */

#ifdef __STDC__

static int strcspn(char *s1, char *s2)

#else

static int strcspn(s1, s2)
char           *s1;
char           *s2;

#endif
{
    register char  *scan1;
    register char  *scan2;
    register int    count;

    count = 0;
    for (scan1 = s1; *scan1 != '\0'; scan1++) {
	for (scan2 = s2; *scan2 != '\0';)	/* ++ moved down. */
	    if (*scan1 == *scan2++)
		return (count);
	count++;
    }
    return (count);
}
#endif


/*
 - regsub - perform substitutions after a regexp match
 */
#ifdef __STDC__

void regsub(regexp *prog, char *source, char *dest)

#else

void regsub(prog, source, dest)
regexp         *prog;
char           *source;
char           *dest;

#endif
{
    register char  *src;
    register char  *dst;
    register char   c;
    register int    no;
    register int    len;
    extern char    *strncpy();

    if (prog == (regexp *)NULL || 
	source == (char *)NULL || dest == (char *)NULL) {
	regerror("NULL parm to regsub");
	return;
    }
    if (UCHARAT(prog->program) != MAGIC) {
	regerror("damaged regexp fed to regsub");
	return;
    }
    src = source;
    dst = dest;
    while ((c = *src++) != '\0') {
	if (c == '&')
	    no = 0;
	else if (c == '\\' && '0' <= *src && *src <= '9')
	    no = *src++ - '0';
	else
	    no = -1;

	if (no < 0) {		/* Ordinary character. */
	    if (c == '\\' && (*src == '\\' || *src == '&'))
		c = *src++;
	    *dst++ = c;
	} else if (prog->startp[no] != (char *)NULL && 
		   prog->endp[no] != (char *)NULL) {
	    len = prog->endp[no] - prog->startp[no];
	    strncpy(dst, prog->startp[no], len);
	    dst += len;
	    if (len != 0 && *(dst - 1) == '\0') {	/* strncpy hit NUL. */
		regerror("damaged match string");
		return;
	    }
	}
    }
    *dst++ = '\0';
}


#ifdef __STDC__

void regerror(char *s)

#else

void regerror(s)
char           *s;

#endif
{
    fprintf(stderr, "regexp(3): %s", s);
    exit(1);
}