lib/pattern.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000 Silicon Graphics, Inc.
 * All Rights Reserved.
 */
#include <string.h>
#include "pattern.h"

/*
 * The routines in this module are used to fill/check a data buffer
 * with/against a known pattern.
 */

int
pattern_check(buf, buflen, pat, patlen, patshift)
char	*buf;
int	buflen;
char	*pat;
int	patlen;
int	patshift;
{
    int		nb, ncmp, nleft;
    char	*cp;

    if (patlen)
	patshift = patshift % patlen;

    cp = buf;
    nleft = buflen;

    /*
     * The following 2 blocks of code are to compare the first patlen
     * bytes of buf.  We need 2 checks if patshift is > 0 since we
     * must check the last (patlen - patshift) bytes, and then the
     * first (patshift) bytes.
     */

    nb = patlen - patshift;
    if (nleft < nb) {
	return (memcmp(cp, pat + patshift, nleft) ? -1 : 0);
    } else {
        if (memcmp(cp, pat + patshift, nb))
	    return -1;

	nleft -= nb;
	cp += nb;
    }

    if (patshift > 0) {
	nb = patshift;
	if (nleft < nb) {
	    return (memcmp(cp, pat, nleft) ? -1 : 0);
	} else {
	    if (memcmp(cp, pat, nb))
		return -1;

	    nleft -= nb;
	    cp += nb;
	}
    }

    /*
     * Now, verify the rest of the buffer using the algorithm described
     * in the function header.
     */

    ncmp = cp - buf;
    while (ncmp < buflen) {
	nb = (ncmp < nleft) ? ncmp : nleft;
	if (memcmp(buf, cp, nb))
	    return -1;

	cp += nb;
	ncmp += nb;
	nleft -= nb;
    }

    return 0;
}

int
pattern_fill(buf, buflen, pat, patlen, patshift)
char	*buf;
int	buflen;
char	*pat;
int	patlen;
int	patshift;
{
    int		trans, ncopied, nleft;
    char	*cp;

    if (patlen)
	patshift = patshift % patlen;

    cp = buf;
    nleft = buflen;

    /*
     * The following 2 blocks of code are to fill the first patlen
     * bytes of buf.  We need 2 sections if patshift is > 0 since we
     * must first copy the last (patlen - patshift) bytes into buf[0]...,
     * and then the first (patshift) bytes of pattern following them.
     */

    trans = patlen - patshift;
    if (nleft < trans) {
	memcpy(cp, pat + patshift, nleft);
	return 0;
    } else {
	memcpy(cp, pat + patshift, trans);
	nleft -= trans;
	cp += trans;
    }

    if (patshift > 0) {
        trans = patshift;
	if (nleft < trans) {
	    memcpy(cp, pat, nleft);
	    return 0;
	} else {
	    memcpy(cp, pat, trans);
	    nleft -= trans;
	    cp += trans;
	}
    }

    /*
     * Now, fill the rest of the buffer using the algorithm described
     * in the function header comment.
     */

    ncopied = cp - buf;
    while (ncopied < buflen) {
	trans = (ncopied < nleft) ? ncopied : nleft;
	memcpy(cp, buf, trans);
	cp += trans;
	ncopied += trans;
	nleft -= trans;
    }

    return(0);
}