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/* $OpenBSD: look.c,v 1.7 2016/09/13 15:29:25 millert 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
ch = tolower(*s2);
if (*s1 != ch)
return (*s1 - ch);
if (ch == '\0')
return (0);
}
}
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