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
