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1 /*
2  * Copyright (c) 2000 Silicon Graphics, Inc.  All Rights Reserved.
3  *
4  * This program is free software; you can redistribute it and/or modify it
5  * under the terms of version 2 of the GNU General Public License as
6  * published by the Free Software Foundation.
7  *
8  * This program is distributed in the hope that it would be useful, but
9  * WITHOUT ANY WARRANTY; without even the implied warranty of
10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
11  *
12  * Further, this software is distributed without any warranty that it is
13  * free of the rightful claim of any third person regarding infringement
14  * or the like.  Any license provided herein, whether implied or
15  * otherwise, applies only to this software file.  Patent licenses, if
16  * any, provided herein do not apply to combinations of this program with
17  * other software, or any other product whatsoever.
18  *
19  * You should have received a copy of the GNU General Public License along
20  * with this program; if not, write the Free Software Foundation, Inc.,
21  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
22  *
23  * Contact information: Silicon Graphics, Inc., 1600 Amphitheatre Pkwy,
24  * Mountain View, CA  94043, or:
25  *
26  * http://www.sgi.com
27  *
28  * For further information regarding this notice, see:
29  *
30  * http://oss.sgi.com/projects/GenInfo/NoticeExplan/
31  */
32 #ifndef _PATTERN_H_
33 #define _PATTERN_H_
34 
35 /*
36  * pattern_check(buf, buflen, pat, patlen, patshift)
37  *
38  * Check a buffer of length buflen against repeated occurrances of
39  * a pattern whose length is patlen.  Patshift can be used to rotate
40  * the pattern by patshift bytes to the left.
41  *
42  * Patshift may be greater than patlen, the pattern will be rotated by
43  * (patshift % patshift) bytes.
44  *
45  * pattern_check returns -1 if the buffer does not contain repeated
46  * occurrances of the indicated pattern (shifted by patshift).
47  *
48  * The algorithm used to check the buffer relies on the fact that buf is
49  * supposed to be repeated copies of pattern.  The basic algorithm is
50  * to validate the first patlen bytes of buf against the pat argument
51  * passed in - then validate the next patlen bytes against the 1st patlen
52  * bytes - the next (2*patlen) bytes against the 1st (2*pathen) bytes, and
53  * so on.  This algorithm only works when the assumption of a buffer full
54  * of repeated copies of a pattern holds, and gives MUCH better results
55  * then walking the buffer byte by byte.
56  *
57  * Performance wise, It appears to be about 5% slower than doing a straight
58  * memcmp of 2 buffers, but the big win is that it does not require a
59  * 2nd comparison buffer, only the pattern.
60  */
61 int pattern_check( char * , int , char * , int , int );
62 
63 /*
64  * pattern_fill(buf, buflen, pat, patlen, patshift)
65  *
66  * Fill a buffer of length buflen with repeated occurrances of
67  * a pattern whose length is patlen.  Patshift can be used to rotate
68  * the pattern by patshift bytes to the left.
69  *
70  * Patshift may be greater than patlen, the pattern will be rotated by
71  * (patshift % patlen) bytes.
72  *
73  * If buflen is not a multiple of patlen, a partial pattern will be written
74  * in the last part of the buffer.  This implies that a buffer which is
75  * shorter than the pattern length will receive only a partial pattern ...
76  *
77  * pattern_fill always returns 0 - no validation of arguments is done.
78  *
79  * The algorithm used to fill the buffer relies on the fact that buf is
80  * supposed to be repeated copies of pattern.  The basic algorithm is
81  * to fill the first patlen bytes of buf with the pat argument
82  * passed in - then copy the next patlen bytes with the 1st patlen
83  * bytes - the next (2*patlen) bytes with the 1st (2*pathen) bytes, and
84  * so on.  This algorithm only works when the assumption of a buffer full
85  * of repeated copies of a pattern holds, and gives MUCH better results
86  * then filling the buffer 1 byte at a time.
87  */
88 int pattern_fill( char * , int , char * , int , int );
89 
90 #endif
91