1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (c) 2000 Silicon Graphics, Inc.
10 * pattern_check(buf, buflen, pat, patlen, patshift)
12 * Check a buffer of length buflen against repeated occurrances of
13 * a pattern whose length is patlen. Patshift can be used to rotate
14 * the pattern by patshift bytes to the left.
16 * Patshift may be greater than patlen, the pattern will be rotated by
17 * (patshift % patshift) bytes.
19 * pattern_check returns -1 if the buffer does not contain repeated
20 * occurrances of the indicated pattern (shifted by patshift).
22 * The algorithm used to check the buffer relies on the fact that buf is
23 * supposed to be repeated copies of pattern. The basic algorithm is
24 * to validate the first patlen bytes of buf against the pat argument
25 * passed in - then validate the next patlen bytes against the 1st patlen
26 * bytes - the next (2*patlen) bytes against the 1st (2*pathen) bytes, and
27 * so on. This algorithm only works when the assumption of a buffer full
28 * of repeated copies of a pattern holds, and gives MUCH better results
29 * then walking the buffer byte by byte.
31 * Performance wise, It appears to be about 5% slower than doing a straight
32 * memcmp of 2 buffers, but the big win is that it does not require a
33 * 2nd comparison buffer, only the pattern.
35 int pattern_check( char * , int , char * , int , int );
38 * pattern_fill(buf, buflen, pat, patlen, patshift)
40 * Fill a buffer of length buflen with repeated occurrances of
41 * a pattern whose length is patlen. Patshift can be used to rotate
42 * the pattern by patshift bytes to the left.
44 * Patshift may be greater than patlen, the pattern will be rotated by
45 * (patshift % patlen) bytes.
47 * If buflen is not a multiple of patlen, a partial pattern will be written
48 * in the last part of the buffer. This implies that a buffer which is
49 * shorter than the pattern length will receive only a partial pattern ...
51 * pattern_fill always returns 0 - no validation of arguments is done.
53 * The algorithm used to fill the buffer relies on the fact that buf is
54 * supposed to be repeated copies of pattern. The basic algorithm is
55 * to fill the first patlen bytes of buf with the pat argument
56 * passed in - then copy the next patlen bytes with the 1st patlen
57 * bytes - the next (2*patlen) bytes with the 1st (2*pathen) bytes, and
58 * so on. This algorithm only works when the assumption of a buffer full
59 * of repeated copies of a pattern holds, and gives MUCH better results
60 * then filling the buffer 1 byte at a time.
62 int pattern_fill( char * , int , char * , int , int );