1 /* $OpenBSD: look.c,v 1.4 2009/10/27 23:59:43 deraadt Exp $ */ 2 3 /*- 4 * Copyright (c) 1991, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * David Hitz of Auspex Systems, Inc. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/types.h> 36 #include <ctype.h> 37 #include <stdio.h> 38 #include <stdlib.h> 39 #include <string.h> 40 #include <err.h> 41 42 u_char *binary_search(u_char *, u_char *, u_char *); 43 u_char *linear_search(u_char *, u_char *, u_char *); 44 int compare(u_char *, u_char *, u_char *); 45 int look(u_char *, u_char *, u_char *); 46 47 int 48 look(u_char *string, u_char *front, u_char *back) 49 { 50 u_char *s; 51 52 /* Convert string to lower case before searching. */ 53 for (s = string; *s; s++) { 54 if (isupper(*s)) 55 *s = _tolower(*s); 56 } 57 58 front = binary_search(string, front, back); 59 front = linear_search(string, front, back); 60 61 return (front != NULL); 62 } 63 64 /* 65 * Binary search for "string" in memory between "front" and "back". 66 * 67 * This routine is expected to return a pointer to the start of a line at 68 * *or before* the first word matching "string". Relaxing the constraint 69 * this way simplifies the algorithm. 70 * 71 * Invariants: 72 * front points to the beginning of a line at or before the first 73 * matching string. 74 * 75 * back points to the beginning of a line at or after the first 76 * matching line. 77 * 78 * Base of the Invariants. 79 * front = NULL; 80 * back = EOF; 81 * 82 * Advancing the Invariants: 83 * 84 * p = first newline after halfway point from front to back. 85 * 86 * If the string at "p" is not greater than the string to match, 87 * p is the new front. Otherwise it is the new back. 88 * 89 * Termination: 90 * 91 * The definition of the routine allows it return at any point, 92 * since front is always at or before the line to print. 93 * 94 * In fact, it returns when the chosen "p" equals "back". This 95 * implies that there exists a string is least half as long as 96 * (back - front), which in turn implies that a linear search will 97 * be no more expensive than the cost of simply printing a string or two. 98 * 99 * Trying to continue with binary search at this point would be 100 * more trouble than it's worth. 101 */ 102 #define SKIP_PAST_NEWLINE(p, back) \ 103 while (p < back && *p++ != '\n'); 104 105 u_char * 106 binary_search(u_char *string, u_char *front, u_char *back) 107 { 108 u_char *p; 109 110 p = front + (back - front) / 2; 111 SKIP_PAST_NEWLINE(p, back); 112 113 /* 114 * If the file changes underneath us, make sure we don't 115 * infinitely loop. 116 */ 117 while (p < back && back > front) { 118 if (compare(string, p, back) > 0) 119 front = p; 120 else 121 back = p; 122 p = front + (back - front) / 2; 123 SKIP_PAST_NEWLINE(p, back); 124 } 125 return (front); 126 } 127 128 /* 129 * Find the first line that matches string, linearly searching from front 130 * to back. 131 * 132 * Return NULL for no such line. 133 * 134 * This routine assumes: 135 * 136 * o front points at the first character in a line. 137 * o front is before or at the first line to be printed. 138 */ 139 u_char * 140 linear_search(u_char *string, u_char *front, u_char *back) 141 { 142 int result; 143 144 while (front < back) { 145 result = compare(string, front, back); 146 if (result == 0) 147 return (front); /* found it */ 148 if (result < 0) 149 return (NULL); /* not there */ 150 151 SKIP_PAST_NEWLINE(front, back); 152 } 153 return (NULL); 154 } 155 156 int 157 compare(u_char *s1, u_char *s2, u_char *back) 158 { 159 int ch; 160 161 /* Note that s1 is already upper case. */ 162 for (;; ++s1, ++s2) { 163 if (*s2 == '\n' || s2 == back) 164 ch = '\0'; 165 else if (isupper(*s2)) 166 ch = _tolower(*s2); 167 else 168 ch = *s2; 169 if (*s1 != ch) 170 return (*s1 - ch); 171 if (ch == '\0') 172 return (0); 173 } 174 } 175