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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 1.13 2009/10/27 23:59:40 deraadt Exp $	*/
/*	$NetBSD: look.c,v 1.7 1995/08/31 22:41:02 jtc 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.
 */

/*
 * look -- find lines in a sorted list.
 * 
 * The man page said that TABs and SPACEs participate in -d comparisons.
 * In fact, they were ignored.  This implements historic practice, not
 * the manual page.
 */

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

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <err.h>

#include "pathnames.h"

/*
 * FOLD and DICT convert characters to a normal form for comparison,
 * according to the user specified flags.
 * 
 * DICT expects integers because it uses a non-character value to
 * indicate a character which should not participate in comparisons.
 */
#define	EQUAL		0
#define	GREATER		1
#define	LESS		(-1)
#define NO_COMPARE	(-2)

#define	FOLD(c)	(isascii(c) && isupper(c) ? tolower(c) : (c))
#define	DICT(c)	(isascii(c) && isalnum(c) ? (c) : NO_COMPARE)

int dflag, fflag;

char	*binary_search(char *, char *, char *);
int	 compare(char *, char *, char *);
char	*linear_search(char *, char *, char *);
int	 look(char *, char *, char *);
void	 print_from(char *, char *, char *);
void	 usage(void);

int
main(int argc, char *argv[])
{
	struct stat sb;
	int ch, fd, termchar;
	char *back, *file, *front, *string, *p;

	file = _PATH_WORDS;
	termchar = '\0';
	while ((ch = getopt(argc, argv, "dft:")) != -1)
		switch(ch) {
		case 'd':
			dflag = 1;
			break;
		case 'f':
			fflag = 1;
			break;
		case 't':
			termchar = *optarg;
			break;
		case '?':
		default:
			usage();
		}
	argc -= optind;
	argv += optind;

	switch (argc) {
	case 2:				/* Don't set -df for user. */
		string = *argv++;
		file = *argv;
		break;
	case 1:				/* But set -df by default. */
		dflag = fflag = 1;
		string = *argv;
		break;
	default:
		usage();
	}

	if (termchar != '\0' && (p = strchr(string, termchar)) != NULL)
		*++p = '\0';

	if ((fd = open(file, O_RDONLY, 0)) < 0 || fstat(fd, &sb))
		err(2, "%s", file);
	if (sb.st_size > SIZE_T_MAX)
		errx(2, "%s: %s", file, strerror(EFBIG));
	if ((front = mmap(NULL,
	    (size_t)sb.st_size, PROT_READ, MAP_PRIVATE, fd, (off_t)0)) == MAP_FAILED)
		err(2, "%s", file);
	back = front + sb.st_size;
	exit(look(string, front, back));
}

int
look(char *string, char *front, char *back)
{
	int ch;
	char *readp, *writep;

	/* Reformat string to avoid doing it multiple times later. */
	for (readp = writep = string; ch = *readp++;) {
		if (fflag)
			ch = FOLD(ch);
		if (dflag)
			ch = DICT(ch);
		if (ch != NO_COMPARE)
			*(writep++) = ch;
	}
	*writep = '\0';

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

	if (front)
		print_from(string, front, back);
	return (front ? 0 : 1);
}


/*
 * 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');

char *
binary_search(char *string, char *front, char *back)
{
	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) == 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.
 */
char *
linear_search(char *string, char *front, char *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);
}

/*
 * Print as many lines as match string, starting at front.
 */
void 
print_from(char *string, char *front, char *back)
{
	for (; front < back && compare(string, front, back) == EQUAL; ++front) {
		for (; front < back && *front != '\n'; ++front)
			if (putchar(*front) == EOF)
				err(2, "stdout");
		if (putchar('\n') == EOF)
			err(2, "stdout");
	}
}

/*
 * 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.
 * 
 * Compare understands about the -f and -d flags, and treats comparisons
 * appropriately.
 * 
 * The string "s1" is null terminated.  The string s2 is '\n' terminated (or
 * "back" terminated).
 */
int
compare(char *s1, char *s2, char *back)
{
	int ch;

	for (; *s1 && s2 < back && *s2 != '\n'; ++s1, ++s2) {
		ch = *s2;
		if (fflag)
			ch = FOLD(ch);
		if (dflag)
			ch = DICT(ch);

		if (ch == NO_COMPARE) {
			++s2;		/* Ignore character in comparison. */
			continue;
		}
		if (*s1 != ch)
			return (*s1 < ch ? LESS : GREATER);
	}
	return (*s1 ? GREATER : EQUAL);
}

void
usage(void)
{
	(void)fprintf(stderr,
	    "usage: look [-df] [-t termchar] string [file]\n");
	exit(2);
}