[unix-history] / usr.bin / vi / nex / ex_tag.c

/*-
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * David Hitz of Auspex Systems, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
static char sccsid[] = "@(#)ex_tag.c	8.31 (Berkeley) 1/22/94";
#endif /* not lint */

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "vi.h"
#include "excmd.h"
#include "tag.h"

static char	*binary_search __P((char *, char *, char *));
static int	 compare __P((char *, char *, char *));
static char	*linear_search __P((char *, char *, char *));
static int	 search __P((SCR *, char *, char *, char **));
static int	 tag_get __P((SCR *, char *, char **, char **, char **));

/*
 * ex_tagfirst --
 *	The tag code can be entered from main, i.e. "vi -t tag".
 */
int
ex_tagfirst(sp, tagarg)
	SCR *sp;
	char *tagarg;
{
	FREF *frp;
	MARK m;
	long tl;
	u_int flags;
	int sval;
	char *p, *tag, *name, *search;

	/* Taglength may limit the number of characters. */
	if ((tl = O_VAL(sp, O_TAGLENGTH)) != 0 && strlen(tagarg) > tl)
		tagarg[tl] = '\0';

	/* Get the tag information. */
	if (tag_get(sp, tagarg, &tag, &name, &search))
		return (1);

	/* Create the file entry. */
	if ((frp = file_add(sp, NULL, name, 0)) == NULL)
		return (1);
	if (file_init(sp, frp, NULL, 0))
		return (1);

	/*
	 * !!!
	 * Historic vi accepted a line number as well as a search
	 * string, and people are apparently still using the format.
	 */
	if (isdigit(search[0])) {
		m.lno = atoi(search);
		m.cno = 0;
	} else {
		/*
		 * Search for the tag; cheap fallback for C functions if
		 * the name is the same but the arguments have changed.
		 */
		m.lno = 1;
		m.cno = 0;
		flags = SEARCH_FILE | SEARCH_TAG | SEARCH_TERM;
		sval = f_search(sp, sp->ep, &m, &m, search, NULL, &flags);
		if (sval && (p = strrchr(search, '(')) != NULL) {
			p[1] = '\0';
			sval = f_search(sp, sp->ep,
			    &m, &m, search, NULL, &flags);
		}
		if (sval)
			msgq(sp, M_ERR, "%s: search pattern not found.", tag);
	}

	/* Set up the screen. */
	frp->lno = m.lno;
	frp->cno = m.cno;
	F_SET(frp, FR_CURSORSET);

	/* Might as well make this the default tag. */
	if ((EXP(sp)->tlast = strdup(tagarg)) == NULL) {
		msgq(sp, M_SYSERR, NULL);
		return (1);
	}
	return (0);
}

/*
 * ex_tagpush -- :tag [file]
 *	Move to a new tag.
 *
 * The tags stacks in nvi are a bit tricky.  Each tag contains a file name,
 * search string, and line/column numbers.  The search string is only used
 * for the first access and for user display.  The first record on the stack
 * is the place where we first did a tag, so it has no search string.  The
 * second record is the first tag, and so on.  Note, this means that the
 * "current" tag is always on the stack.  Each tag has a line/column which is
 * the location from which the user tagged the following TAG entry, and which
 * is used as the return location.
 */
int
ex_tagpush(sp, ep, cmdp)
	SCR *sp;
	EXF *ep;
	EXCMDARG *cmdp;
{
	enum {TC_CHANGE, TC_CURRENT} which;
	EX_PRIVATE *exp;
	FREF *frp;
	MARK m;
	TAG *tp;
	u_int flags;
	int sval;
	long tl;
	char *name, *p, *search, *tag;
	
	exp = EXP(sp);
	switch (cmdp->argc) {
	case 1:
		if (exp->tlast != NULL)
			FREE(exp->tlast, strlen(exp->tlast) + 1);
		if ((exp->tlast = strdup(cmdp->argv[0]->bp)) == NULL) {
			msgq(sp, M_SYSERR, NULL);
			return (1);
		}
		break;
	case 0:
		if (exp->tlast == NULL) {
			msgq(sp, M_ERR, "No previous tag entered.");
			return (1);
		}
		break;
	default:
		abort();
	}

	/* Taglength may limit the number of characters. */
	if ((tl = O_VAL(sp, O_TAGLENGTH)) != 0 && strlen(exp->tlast) > tl)
		exp->tlast[tl] = '\0';

	/* Get the tag information. */
	if (tag_get(sp, exp->tlast, &tag, &name, &search))
		return (1);

	/* Get a new FREF structure. */
	if ((frp = file_add(sp, sp->frp, name, 1)) == NULL) {
		FREE(tag, strlen(tag));
		return (1);
	}

	/*
	 * Get a tag structure -- if this is the first tag, push it on the
	 * stack as a placeholder and get another tag structure.  Set the
	 * line/column of the most recent element on the stack to be the
	 * current values, including the file pointer.  Then push the new
	 * TAG onto the stack with the new file and search string for user
	 * display.
	 */
	CALLOC(sp, tp, TAG *, 1, sizeof(TAG));
	if (tp != NULL && exp->tagq.tqh_first == NULL) {
		TAILQ_INSERT_HEAD(&exp->tagq, tp, q);
		CALLOC(sp, tp, TAG *, 1, sizeof(TAG));
	}
	if (exp->tagq.tqh_first != NULL) {
		exp->tagq.tqh_first->frp = sp->frp;
		exp->tagq.tqh_first->lno = sp->lno;
		exp->tagq.tqh_first->cno = sp->cno;
	}
	if (tp != NULL) {
		if ((tp->search = strdup(search)) == NULL)
			msgq(sp, M_SYSERR, NULL);
		else
			tp->slen = strlen(search);
		tp->frp = frp;
		TAILQ_INSERT_HEAD(&exp->tagq, tp, q);
	}

	/* Switch to the new file. */
	if (sp->frp == frp)
		which = TC_CURRENT;
	else {
		MODIFY_CHECK(sp, sp->ep, F_ISSET(cmdp, E_FORCE));

		if (file_init(sp, frp, NULL, 0)) {
			if (tp != NULL)
				FREE(tp, sizeof(TAG));
			FREE(tag, strlen(tag));
			return (1);
		}
		which = TC_CHANGE;
	}

	/*
	 * !!!
	 * Historic vi accepted a line number as well as a search
	 * string, and people are apparently still using the format.
	 */
	if (isdigit(search[0])) {
		m.lno = atoi(search);
		m.cno = 0;
		sval = 0;
	} else {
		/*
		 * Search for the tag; cheap fallback for C functions
		 * if the name is the same but the arguments have changed.
		 */
		m.lno = 1;
		m.cno = 0;
		flags = SEARCH_FILE | SEARCH_TAG | SEARCH_TERM;
		sval = f_search(sp, sp->ep, &m, &m, search, NULL, &flags);
		if (sval && (p = strrchr(search, '(')) != NULL) {
			p[1] = '\0';
			sval = f_search(sp, sp->ep,
			     &m, &m, search, NULL, &flags);
			p[1] = '(';
		}
		if (sval)
			msgq(sp, M_ERR, "%s: search pattern not found.", tag);
	}
	free(tag);

	switch (which) {
	case TC_CHANGE:
		frp->lno = m.lno;
		frp->cno = m.cno;
		F_SET(frp, FR_CURSORSET);
		F_SET(sp, S_FSWITCH);
		break;
	case TC_CURRENT:
		if (sval)
			return (1);
		sp->lno = m.lno;
		sp->cno = m.cno;
		break;
	}
	return (0);
}

/* Free a tag or tagf structure from a queue. */
#define	FREETAG(tp) {							\
	TAILQ_REMOVE(&exp->tagq, (tp), q);				\
	if ((tp)->search != NULL)					\
		free((tp)->search);					\
	FREE((tp), sizeof(TAGF));					\
}
#define	FREETAGF(tfp) {							\
	TAILQ_REMOVE(&exp->tagfq, (tfp), q);				\
	free((tfp)->name);						\
	FREE((tfp), sizeof(TAGF));					\
}

/*
 * ex_tagpop -- :tagp[op][!] [number | file]
 *	Pop the tag stack.
 */
int
ex_tagpop(sp, ep, cmdp)
	SCR *sp;
	EXF *ep;
	EXCMDARG *cmdp;
{
	EX_PRIVATE *exp;
	TAG *ntp, *tp;
	recno_t lno;
	long off, saved_off;
	size_t arglen, cno;
	char *arg, *p, *t;

	/* Check for an empty stack. */
	exp = EXP(sp);
	if (exp->tagq.tqh_first == NULL) {
		msgq(sp, M_INFO, "The tags stack is empty.");
		return (1);
	}

	switch (cmdp->argc) {
	case 0:				/* Pop one tag. */
		tp = exp->tagq.tqh_first;
		FREETAG(tp);
		break;
	case 1:				/* Name or number. */
		arg = cmdp->argv[0]->bp;
		saved_off = strtol(arg, &p, 10);
		if (*p == '\0') {
			if (saved_off < 1)
				return (0);
			for (tp = exp->tagq.tqh_first, off = saved_off;
			    tp != NULL && off-- > 1; tp = tp->q.tqe_next);
			if (tp == NULL) {
				msgq(sp, M_ERR,
"Less than %d entries on the tags stack; use :display to see the tags stack.",
				    saved_off);
				return (1);
			}
			for (off = saved_off; off-- > 1;) {
				tp = exp->tagq.tqh_first;
				FREETAG(tp);
			}
		} else {
			arglen = strlen(arg);
			for (tp = exp->tagq.tqh_first;
			    tp != NULL; tp = tp->q.tqe_next) {
				/* Use the user's original file name. */
				p = tp->frp->name;
				if ((t = strrchr(p, '/')) == NULL)
					t = p;
				else
					++t;
				if (!strncmp(arg, t, arglen)) {
					ntp = tp;
					break;
				}
			}
			if (tp == NULL) {
				msgq(sp, M_ERR,
"No file named %s on the tags stack; use :display to see the tags stack.",
				    arg);
				return (1);
			}
			for (;;) {
				tp = exp->tagq.tqh_first;
				if (tp == ntp)
					break;
				FREETAG(tp);
			}
		}
		break;
	default:
		abort();
	}

	/* Update the cursor from the saved TAG information. */
	tp = exp->tagq.tqh_first;
	if (tp->frp == sp->frp) {
		sp->lno = tp->lno;
		sp->cno = tp->cno;
	} else {
		MODIFY_CHECK(sp, ep, F_ISSET(cmdp, E_FORCE));

		if (file_init(sp, tp->frp, NULL, 0))
			return (1);

		tp->frp->lno = tp->lno;
		tp->frp->cno = tp->cno;
		F_SET(sp->frp, FR_CURSORSET);

		F_SET(sp, S_FSWITCH);
	}

	/* If returning to the first tag, the stack is now empty. */
	if (tp->q.tqe_next == NULL)
		FREETAG(tp);
	return (0);
}

/*
 * ex_tagtop -- :tagt[op][!]
 *	Clear the tag stack.
 */	
int
ex_tagtop(sp, ep, cmdp)
	SCR *sp;
	EXF *ep;
	EXCMDARG *cmdp;
{
	EX_PRIVATE *exp;
	TAG *tp, tmp;
	int found;

	/* Pop to oldest saved information. */
	exp = EXP(sp);
	for (found = 0; (tp = exp->tagq.tqh_first) != NULL; found = 1) {
		if (exp->tagq.tqh_first == NULL)
			tmp = *tp;
		FREETAG(tp);
	}

	if (!found) {
		msgq(sp, M_INFO, "The tags stack is empty.");
		return (1);
	}

	/* If not switching files, it's easy; else do the work. */
	if (tmp.frp == sp->frp) {
		sp->lno = tmp.lno;
		sp->cno = tmp.cno;
	} else {
		MODIFY_CHECK(sp, sp->ep, F_ISSET(cmdp, E_FORCE));

		if (file_init(sp, tmp.frp, NULL, 0))
			return (1);

		tmp.frp->lno = tmp.lno;
		tmp.frp->cno = tmp.cno;

		F_SET(sp->frp, FR_CURSORSET);

		F_SET(sp, S_FSWITCH);
	}
	return (0);
}

/*
 * ex_tagdisplay --
 *	Display the list of tags.
 */
int
ex_tagdisplay(sp, ep)
	SCR *sp;
	EXF *ep;
{
	EX_PRIVATE *exp;
	TAG *tp;
	size_t len, maxlen;
	int cnt;
	char *name;

	exp = EXP(sp);
	if ((tp = exp->tagq.tqh_first) == NULL) {
		(void)ex_printf(EXCOOKIE, "No tags to display.\n");
		return (0);
	}

	/*
	 * Figure out the formatting.  MNOC is the maximum
	 * number of file name columns before we split the line.
	 */
#define	MNOC	15
	for (maxlen = 0,
	    tp = exp->tagq.tqh_first; tp != NULL; tp = tp->q.tqe_next) {
		len = strlen(name = tp->frp->name);	/* The original name. */
		if (maxlen < len && len < MNOC)
			maxlen = len;
	}

	for (cnt = 1, tp = exp->tagq.tqh_first; tp != NULL;
	    ++cnt, tp = tp->q.tqe_next) {
		len = strlen(name = tp->frp->name);	/* The original name. */
		if (len > maxlen || len + tp->slen > sp->cols)
			if (tp == NULL || tp->search == NULL)
				(void)ex_printf(EXCOOKIE,
				    "%2d %s\n", cnt, name);
			else
				(void)ex_printf(EXCOOKIE,
				     "%2d %s\n** %*.*s %s\n", cnt, name,
				     (int)maxlen, (int)maxlen, "", tp->search);
		else
			if (tp == NULL || tp->search == NULL)
				(void)ex_printf(EXCOOKIE, "%2d %*.*s\n",
				    cnt, (int)maxlen, (int)len, name);
			else
				(void)ex_printf(EXCOOKIE, "%2d %*.*s %s\n",
				    cnt, (int)maxlen, (int)len, name,
				    tp->search);
	}
	return (0);
}

/*
 * ex_tagalloc --
 *	Create a new list of tag files.
 */
int
ex_tagalloc(sp, str)
	SCR *sp;
	char *str;
{
	EX_PRIVATE *exp;
	TAGF *tp;
	size_t len;
	char *p, *t;

	/* Free current queue. */
	exp = EXP(sp);
	while ((tp = exp->tagfq.tqh_first) != NULL)
		FREETAGF(tp);

	/* Create new queue. */
	for (p = t = str;; ++p) {
		if (*p == '\0' || isblank(*p)) {
			if ((len = p - t) > 1) {
				MALLOC_RET(sp, tp, TAGF *, sizeof(TAGF));
				MALLOC(sp, tp->name, char *, len + 1);
				if (tp->name == NULL) {
					FREE(tp, sizeof(TAGF));
					return (1);
				}
				memmove(tp->name, t, len);
				tp->name[len] = '\0';
				tp->flags = 0;
				TAILQ_INSERT_TAIL(&exp->tagfq, tp, q);
			}
			t = p + 1;
		}
		if (*p == '\0')
			 break;
	}
	return (0);
}
						/* Free previous queue. */
/*
 * ex_tagfree --
 *	Free the tags file list.
 */
int
ex_tagfree(sp)
	SCR *sp;
{
	EX_PRIVATE *exp;
	TAG *tp;
	TAGF *tfp;

	/* Free up tag information. */
	exp = EXP(sp);
	while ((tp = exp->tagq.tqh_first) != NULL)
		FREETAG(tp);
	while ((tfp = exp->tagfq.tqh_first) != NULL)
		FREETAGF(tfp);
	FREE(exp->tlast, strlen(exp->tlast) + 1);
	return (0);
}

/*
 * ex_tagcopy --
 *	Copy a screen's tag structures.
 */
int
ex_tagcopy(orig, sp)
	SCR *orig, *sp;
{
	EX_PRIVATE *oexp, *nexp;
	TAG *ap, *tp;
	TAGF *atfp, *tfp;

	/* Copy tag stack. */
	oexp = EXP(orig);
	nexp = EXP(sp);
	for (ap = oexp->tagq.tqh_first; ap != NULL; ap = ap->q.tqe_next) {
		MALLOC(sp, tp, TAG *, sizeof(TAG));
		if (tp == NULL)
			goto nomem;
		*tp = *ap;
		if (ap->search != NULL &&
		    (tp->search = strdup(ap->search)) == NULL)
			goto nomem;
		TAILQ_INSERT_TAIL(&nexp->tagq, tp, q);
	}

	/* Copy list of tag files. */
	for (atfp = oexp->tagfq.tqh_first;
	    atfp != NULL; atfp = atfp->q.tqe_next) {
		MALLOC(sp, tfp, TAGF *, sizeof(TAGF));
		if (tfp == NULL)
			goto nomem;
		*tfp = *atfp;
		if ((tfp->name = strdup(atfp->name)) == NULL)
			goto nomem;
		TAILQ_INSERT_TAIL(&nexp->tagfq, tfp, q);
	}
		
	/* Copy the last tag. */
	if (oexp->tlast != NULL &&
	    (nexp->tlast = strdup(oexp->tlast)) == NULL) {
nomem:		msgq(sp, M_SYSERR, NULL);
		return (1);
	}
	return (0);
}

/*
 * tag_get --
 *	Get a tag from the tags files.
 */
static int
tag_get(sp, tag, tagp, filep, searchp)
	SCR *sp;
	char *tag, **tagp, **filep, **searchp;
{
	EX_PRIVATE *exp;
	TAGF *tfp;
	int dne;
	char *p;

	/*
	 * Find the tag, only display missing file messages once, and
	 * then only if we didn't find the tag.
	 */
	dne = 0;
	exp = EXP(sp);
	for (p = NULL, tfp = exp->tagfq.tqh_first;
	    tfp != NULL && p == NULL; tfp = tfp->q.tqe_next) {
		errno = 0;
		F_CLR(tfp, TAGF_DNE);
		if (search(sp, tfp->name, tag, &p))
			if (errno == ENOENT) {
				if (!F_ISSET(tfp, TAGF_DNE_WARN)) {
					dne = 1;
					F_SET(tfp, TAGF_DNE);
				}
			} else
				msgq(sp, M_SYSERR, tfp->name);
	}
	
	if (p == NULL) {
		msgq(sp, M_ERR, "%s: tag not found.", tag);
		if (dne)
			for (tfp = exp->tagfq.tqh_first;
			    tfp != NULL; tfp = tfp->q.tqe_next)
				if (F_ISSET(tfp, TAGF_DNE)) {
					errno = ENOENT;
					msgq(sp, M_SYSERR, tfp->name);
					F_SET(tfp, TAGF_DNE_WARN);
				}
		return (1);
	}

	/*
	 * Set the return pointers; tagp points to the tag, and, incidentally
	 * the allocated string, filep points to the nul-terminated file name,
	 * searchp points to the nul-terminated search string.
	 */
	for (*tagp = p; *p && !isblank(*p); ++p);
	if (*p == '\0')
		goto malformed;
	for (*p++ = '\0'; isblank(*p); ++p);
	for (*filep = p; *p && !isblank(*p); ++p);
	if (*p == '\0')
		goto malformed;
	for (*p++ = '\0'; isblank(*p); ++p);
	*searchp = p;
	if (*p == '\0') {
malformed:	free(*tagp);
		msgq(sp, M_ERR, "%s: corrupted tag in %s.", tag, tfp->name);
		return (1);
	}
	return (0);
}

#define	EQUAL		0
#define	GREATER		1
#define	LESS		(-1)

/*
 * search --
 *	Search a file for a tag.
 */
static int
search(sp, name, tname, tag)
	SCR *sp;
	char *name, *tname, **tag;
{
	struct stat sb;
	int fd, len;
	char *endp, *back, *front, *map, *p;

	if ((fd = open(name, O_RDONLY, 0)) < 0)
		return (1);

	/*
	 * XXX
	 * We'd like to test if the file is too big to mmap.  Since we don't
	 * know what size or type off_t's or size_t's are, what the largest
	 * unsigned integral type is, or what random insanity the local C
	 * compiler will perpetrate, doing the comparison in a portable way
	 * is flatly impossible.  Hope that malloc fails if the file is too
	 * large.
	 */
	if (fstat(fd, &sb) || (map = mmap(NULL, (size_t)sb.st_size,
	    PROT_READ, MAP_PRIVATE, fd, (off_t)0)) == (caddr_t)-1) {
		(void)close(fd);
		return (1);
	}
	front = map;
	back = front + sb.st_size;

	front = binary_search(tname, front, back);
	front = linear_search(tname, front, back);

	if (front == NULL || (endp = strchr(front, '\n')) == NULL) {
		*tag = NULL;
		goto done;
	}

	len = endp - front;
	MALLOC(sp, p, char *, len + 1);
	if (p == NULL) {
		*tag = NULL;
		goto done;
	}
	memmove(p, front, len);
	p[len] = '\0';
	*tag = p;

done:	if (munmap(map, (size_t)sb.st_size))
		msgq(sp, M_SYSERR, "munmap");
	if (close(fd))
		msgq(sp, M_SYSERR, "close");
	return (0);
}

/*
 * Binary search for "string" in memory between "front" and "back".
 * 
 * This routine is expected to return a pointer to the start of a line at
 * *or before* the first word matching "string".  Relaxing the constraint
 * this way simplifies the algorithm.
 * 
 * Invariants:
 * 	front points to the beginning of a line at or before the first 
 *	matching string.
 * 
 * 	back points to the beginning of a line at or after the first 
 *	matching line.
 * 
 * Base of the Invariants.
 * 	front = NULL; 
 *	back = EOF;
 * 
 * Advancing the Invariants:
 * 
 * 	p = first newline after halfway point from front to back.
 * 
 * 	If the string at "p" is not greater than the string to match, 
 *	p is the new front.  Otherwise it is the new back.
 * 
 * Termination:
 * 
 * 	The definition of the routine allows it return at any point, 
 *	since front is always at or before the line to print.
 * 
 * 	In fact, it returns when the chosen "p" equals "back".  This 
 *	implies that there exists a string is least half as long as 
 *	(back - front), which in turn implies that a linear search will 
 *	be no more expensive than the cost of simply printing a string or two.
 * 
 * 	Trying to continue with binary search at this point would be 
 *	more trouble than it's worth.
 */
#define	SKIP_PAST_NEWLINE(p, back)	while (p < back && *p++ != '\n');

static char *
binary_search(string, front, back)
	register char *string, *front, *back;
{
	register char *p;

	p = front + (back - front) / 2;
	SKIP_PAST_NEWLINE(p, back);

	while (p != back) {
		if (compare(string, p, back) == GREATER)
			front = p;
		else
			back = p;
		p = front + (back - front) / 2;
		SKIP_PAST_NEWLINE(p, back);
	}
	return (front);
}

/*
 * Find the first line that starts with string, linearly searching from front
 * to back.
 * 
 * Return NULL for no such line.
 * 
 * This routine assumes:
 * 
 * 	o front points at the first character in a line. 
 *	o front is before or at the first line to be printed.
 */
static char *
linear_search(string, front, back)
	char *string, *front, *back;
{
	while (front < back) {
		switch (compare(string, front, back)) {
		case EQUAL:		/* Found it. */
			return (front);
			break;
		case LESS:		/* No such string. */
			return (NULL);
			break;
		case GREATER:		/* Keep going. */
			break;
		}
		SKIP_PAST_NEWLINE(front, back);
	}
	return (NULL);
}

/*
 * Return LESS, GREATER, or EQUAL depending on how the string1 compares
 * with string2 (s1 ??? s2).
 * 
 * 	o Matches up to len(s1) are EQUAL. 
 *	o Matches up to len(s2) are GREATER.
 * 
 * The string "s1" is null terminated.  The string s2 is '\t', space, (or
 * "back") terminated.
 *
 * !!!
 * Reasonably modern ctags programs use tabs as separators, not spaces.
 * However, historic programs did use spaces, and, I got complaints.
 */
static int
compare(s1, s2, back)
	register char *s1, *s2, *back;
{
	for (; *s1 && s2 < back && (*s2 != '\t' && *s2 != ' '); ++s1, ++s2)
		if (*s1 != *s2)
			return (*s1 < *s2 ? LESS : GREATER);
	return (*s1 ? GREATER : s2 < back &&
	    (*s2 != '\t' && *s2 != ' ') ? LESS : EQUAL);
}