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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2000 Silicon Graphics, Inc.
* All Rights Reserved.
*/
#ifndef _PATTERN_H_
#define _PATTERN_H_
/*
* pattern_check(buf, buflen, pat, patlen, patshift)
*
* Check a buffer of length buflen against repeated occurrances of
* a pattern whose length is patlen. Patshift can be used to rotate
* the pattern by patshift bytes to the left.
*
* Patshift may be greater than patlen, the pattern will be rotated by
* (patshift % patshift) bytes.
*
* pattern_check returns -1 if the buffer does not contain repeated
* occurrances of the indicated pattern (shifted by patshift).
*
* The algorithm used to check the buffer relies on the fact that buf is
* supposed to be repeated copies of pattern. The basic algorithm is
* to validate the first patlen bytes of buf against the pat argument
* passed in - then validate the next patlen bytes against the 1st patlen
* bytes - the next (2*patlen) bytes against the 1st (2*pathen) bytes, and
* so on. This algorithm only works when the assumption of a buffer full
* of repeated copies of a pattern holds, and gives MUCH better results
* then walking the buffer byte by byte.
*
* Performance wise, It appears to be about 5% slower than doing a straight
* memcmp of 2 buffers, but the big win is that it does not require a
* 2nd comparison buffer, only the pattern.
*/
int pattern_check( char * , int , char * , int , int );
/*
* pattern_fill(buf, buflen, pat, patlen, patshift)
*
* Fill a buffer of length buflen with repeated occurrances of
* a pattern whose length is patlen. Patshift can be used to rotate
* the pattern by patshift bytes to the left.
*
* Patshift may be greater than patlen, the pattern will be rotated by
* (patshift % patlen) bytes.
*
* If buflen is not a multiple of patlen, a partial pattern will be written
* in the last part of the buffer. This implies that a buffer which is
* shorter than the pattern length will receive only a partial pattern ...
*
* pattern_fill always returns 0 - no validation of arguments is done.
*
* The algorithm used to fill the buffer relies on the fact that buf is
* supposed to be repeated copies of pattern. The basic algorithm is
* to fill the first patlen bytes of buf with the pat argument
* passed in - then copy the next patlen bytes with the 1st patlen
* bytes - the next (2*patlen) bytes with the 1st (2*pathen) bytes, and
* so on. This algorithm only works when the assumption of a buffer full
* of repeated copies of a pattern holds, and gives MUCH better results
* then filling the buffer 1 byte at a time.
*/
int pattern_fill( char * , int , char * , int , int );
#endif
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