186 lines
5.3 KiB
C
186 lines
5.3 KiB
C
/* $NetBSD: look.c,v 1.2 2005/06/30 16:25:05 christos Exp $ */
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/* derived from: OpenBSD: look.c,v 1.3 2003/06/03 02:56:16 millert Exp */
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/*-
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* Copyright (c) 1991, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* David Hitz of Auspex Systems, Inc.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef lint
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#if 0
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static const char sccsid[] = "@(#)look.c 8.2 (Berkeley) 5/4/95";
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#endif
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static const char rcsid[] = "$NetBSD: look.c,v 1.2 2005/06/30 16:25:05 christos Exp $";
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#endif /* not lint */
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#include <sys/types.h>
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#include <ctype.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <err.h>
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#include "extern.h"
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static u_char *binary_search(u_char *, u_char *, u_char *);
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static u_char *linear_search(u_char *, u_char *, u_char *);
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static int compare(u_char *, u_char *, u_char *);
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int
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look(u_char *string, u_char *front, u_char *back)
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{
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u_char *s;
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/* Convert string to lower case before searching. */
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for (s = string; *s; s++) {
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if (isupper(*s))
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*s = _tolower(*s);
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}
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front = binary_search(string, front, back);
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front = linear_search(string, front, back);
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return (front != NULL);
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}
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/*
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* Binary search for "string" in memory between "front" and "back".
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*
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* This routine is expected to return a pointer to the start of a line at
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* *or before* the first word matching "string". Relaxing the constraint
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* this way simplifies the algorithm.
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*
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* Invariants:
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* front points to the beginning of a line at or before the first
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* matching string.
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*
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* back points to the beginning of a line at or after the first
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* matching line.
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*
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* Base of the Invariants.
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* front = NULL;
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* back = EOF;
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*
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* Advancing the Invariants:
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*
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* p = first newline after halfway point from front to back.
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*
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* If the string at "p" is not greater than the string to match,
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* p is the new front. Otherwise it is the new back.
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*
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* Termination:
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*
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* The definition of the routine allows it return at any point,
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* since front is always at or before the line to print.
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*
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* In fact, it returns when the chosen "p" equals "back". This
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* implies that there exists a string is least half as long as
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* (back - front), which in turn implies that a linear search will
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* be no more expensive than the cost of simply printing a string or two.
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*
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* Trying to continue with binary search at this point would be
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* more trouble than it's worth.
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*/
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#define SKIP_PAST_NEWLINE(p, back) \
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while (p < back && *p++ != '\n') \
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continue;
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static u_char *
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binary_search(u_char *string, u_char *front, u_char *back)
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{
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u_char *p;
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p = front + (back - front) / 2;
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SKIP_PAST_NEWLINE(p, back);
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/*
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* If the file changes underneath us, make sure we don't
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* infinitely loop.
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*/
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while (p < back && back > front) {
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if (compare(string, p, back) > 0)
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front = p;
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else
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back = p;
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p = front + (back - front) / 2;
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SKIP_PAST_NEWLINE(p, back);
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}
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return (front);
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}
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/*
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* Find the first line that matches string, linearly searching from front
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* to back.
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*
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* Return NULL for no such line.
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*
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* This routine assumes:
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*
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* o front points at the first character in a line.
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* o front is before or at the first line to be printed.
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*/
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static u_char *
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linear_search(u_char *string, u_char *front, u_char *back)
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{
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int result;
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while (front < back) {
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result = compare(string, front, back);
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if (result == 0)
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return (front); /* found it */
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if (result < 0)
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return (NULL); /* not there */
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SKIP_PAST_NEWLINE(front, back);
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}
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return (NULL);
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}
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static int
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compare(u_char *s1, u_char *s2, u_char *back)
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{
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int ch;
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/* Note that s1 is already upper case. */
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for (;; ++s1, ++s2) {
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if (*s2 == '\n' || s2 == back)
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ch = '\0';
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else if (isupper(*s2))
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ch = _tolower(*s2);
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else
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ch = *s2;
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if (*s1 != ch)
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return (*s1 - ch);
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if (ch == '\0')
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return (0);
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}
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}
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