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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*	$OpenBSD: look.c,v 1.4 2009/10/27 23:59:43 deraadt Exp $	*/

/*-
 * Copyright (c) 1991, 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. 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.
 */

#include <sys/types.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>

u_char	*binary_search(u_char *, u_char *, u_char *);
u_char	*linear_search(u_char *, u_char *, u_char *);
int	 compare(u_char *, u_char *, u_char *);
int	 look(u_char *, u_char *, u_char *);

int
look(u_char *string, u_char *front, u_char *back)
{
	u_char *s;

	/* Convert string to lower case before searching. */
	for (s = string; *s; s++) {
		if (isupper(*s))
			*s = _tolower(*s);
	}

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

	return (front != NULL);
}

/*
 * 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');

u_char *
binary_search(u_char *string, u_char *front, u_char *back)
{
	u_char *p;

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

	/*
	 * If the file changes underneath us, make sure we don't
	 * infinitely loop.
	 */
	while (p < back && back > front) {
		if (compare(string, p, back) > 0)
			front = p;
		else
			back = p;
		p = front + (back - front) / 2;
		SKIP_PAST_NEWLINE(p, back);
	}
	return (front);
}

/*
 * Find the first line that matches 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.
 */
u_char *
linear_search(u_char *string, u_char *front, u_char *back)
{
	int result;

	while (front < back) {
		result = compare(string, front, back);
		if (result == 0)
			return (front);	/* found it */
		if (result < 0)
			return (NULL);	/* not there */

		SKIP_PAST_NEWLINE(front, back);
	}
	return (NULL);
}

int
compare(u_char *s1, u_char *s2, u_char *back)
{
	int ch;

	/* Note that s1 is already upper case. */
	for (;; ++s1, ++s2) {
		if (*s2 == '\n' || s2 == back)
			ch = '\0';
		else if (isupper(*s2))
			ch = _tolower(*s2);
		else
			ch = *s2;
		if (*s1 != ch)
			return (*s1 - ch);
		if (ch == '\0')
			return (0);
	}
}