/* $OpenBSD: look.c,v 1.3 2003/06/03 02:56:16 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. */ #ifndef lint #if 0 static const char sccsid[] = "@(#)look.c 8.2 (Berkeley) 5/4/95"; #endif static const char rcsid[] = "$OpenBSD: look.c,v 1.3 2003/06/03 02:56:16 millert Exp $"; #endif /* not lint */ #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); } }