Annotation of src/usr.bin/spell/look.c, Revision 1.1
1.1 ! millert 1: /* $OpenBSD: look.c,v 1.7 2002/02/16 21:27:48 millert 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. All advertising materials mentioning features or use of this software
! 19: * must display the following acknowledgement:
! 20: * This product includes software developed by the University of
! 21: * California, Berkeley and its contributors.
! 22: * 4. Neither the name of the University nor the names of its contributors
! 23: * may be used to endorse or promote products derived from this software
! 24: * without specific prior written permission.
! 25: *
! 26: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
! 27: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! 28: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! 29: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
! 30: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! 31: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! 32: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! 33: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! 34: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! 35: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! 36: * SUCH DAMAGE.
! 37: */
! 38:
! 39: #ifndef lint
! 40: #if 0
! 41: static const char sccsid[] = "@(#)look.c 8.2 (Berkeley) 5/4/95";
! 42: #endif
! 43: static const char rcsid[] = "$OpenBSD: look.c,v 1.7 2002/02/16 21:27:48 millert Exp $";
! 44: #endif /* not lint */
! 45:
! 46: #include <sys/types.h>
! 47: #include <ctype.h>
! 48: #include <stdio.h>
! 49: #include <stdlib.h>
! 50: #include <string.h>
! 51: #include <err.h>
! 52:
! 53: u_char *binary_search(u_char *, u_char *, u_char *);
! 54: u_char *linear_search(u_char *, u_char *, u_char *);
! 55: int compare(u_char *, u_char *, u_char *);
! 56: int look(u_char *, u_char *, u_char *);
! 57:
! 58: int
! 59: look(u_char *string, u_char *front, u_char *back)
! 60: {
! 61: u_char *s;
! 62:
! 63: /* Convert string to lower case before searching. */
! 64: for (s = string; *s; s++) {
! 65: if (isupper(*s))
! 66: *s = _tolower(*s);
! 67: }
! 68:
! 69: front = binary_search(string, front, back);
! 70: front = linear_search(string, front, back);
! 71:
! 72: return (front != NULL);
! 73: }
! 74:
! 75: /*
! 76: * Binary search for "string" in memory between "front" and "back".
! 77: *
! 78: * This routine is expected to return a pointer to the start of a line at
! 79: * *or before* the first word matching "string". Relaxing the constraint
! 80: * this way simplifies the algorithm.
! 81: *
! 82: * Invariants:
! 83: * front points to the beginning of a line at or before the first
! 84: * matching string.
! 85: *
! 86: * back points to the beginning of a line at or after the first
! 87: * matching line.
! 88: *
! 89: * Base of the Invariants.
! 90: * front = NULL;
! 91: * back = EOF;
! 92: *
! 93: * Advancing the Invariants:
! 94: *
! 95: * p = first newline after halfway point from front to back.
! 96: *
! 97: * If the string at "p" is not greater than the string to match,
! 98: * p is the new front. Otherwise it is the new back.
! 99: *
! 100: * Termination:
! 101: *
! 102: * The definition of the routine allows it return at any point,
! 103: * since front is always at or before the line to print.
! 104: *
! 105: * In fact, it returns when the chosen "p" equals "back". This
! 106: * implies that there exists a string is least half as long as
! 107: * (back - front), which in turn implies that a linear search will
! 108: * be no more expensive than the cost of simply printing a string or two.
! 109: *
! 110: * Trying to continue with binary search at this point would be
! 111: * more trouble than it's worth.
! 112: */
! 113: #define SKIP_PAST_NEWLINE(p, back) \
! 114: while (p < back && *p++ != '\n');
! 115:
! 116: u_char *
! 117: binary_search(u_char *string, u_char *front, u_char *back)
! 118: {
! 119: u_char *p;
! 120:
! 121: p = front + (back - front) / 2;
! 122: SKIP_PAST_NEWLINE(p, back);
! 123:
! 124: /*
! 125: * If the file changes underneath us, make sure we don't
! 126: * infinitely loop.
! 127: */
! 128: while (p < back && back > front) {
! 129: if (compare(string, p, back) > 0)
! 130: front = p;
! 131: else
! 132: back = p;
! 133: p = front + (back - front) / 2;
! 134: SKIP_PAST_NEWLINE(p, back);
! 135: }
! 136: return (front);
! 137: }
! 138:
! 139: /*
! 140: * Find the first line that matches string, linearly searching from front
! 141: * to back.
! 142: *
! 143: * Return NULL for no such line.
! 144: *
! 145: * This routine assumes:
! 146: *
! 147: * o front points at the first character in a line.
! 148: * o front is before or at the first line to be printed.
! 149: */
! 150: u_char *
! 151: linear_search(u_char *string, u_char *front, u_char *back)
! 152: {
! 153: int result;
! 154:
! 155: while (front < back) {
! 156: result = compare(string, front, back);
! 157: if (result == 0)
! 158: return(front); /* found it */
! 159: if (result < 0)
! 160: return(NULL); /* not there */
! 161:
! 162: SKIP_PAST_NEWLINE(front, back);
! 163: }
! 164: return (NULL);
! 165: }
! 166:
! 167: int
! 168: compare(u_char *s1, u_char *s2, u_char *back)
! 169: {
! 170: int ch;
! 171:
! 172: /* Note that s1 is already upper case. */
! 173: for (;; ++s1, ++s2) {
! 174: if (*s2 == '\n' || s2 == back)
! 175: ch = '\0';
! 176: else if (isupper(*s2))
! 177: ch = _tolower(*s2);
! 178: else
! 179: ch = *s2;
! 180: if (*s1 != ch)
! 181: return(*s1 - ch);
! 182: if (ch == '\0')
! 183: return(0);
! 184: }
! 185: }
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