/*      $NetBSD: bm.c,v 1.13 2014/06/23 10:43:25 shm Exp $      */

/*-
 * Copyright (c) 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Andrew Hume of AT&T Bell Laboratories.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)bm.c        8.7 (Berkeley) 6/21/94";
#else
__RCSID("$NetBSD: bm.c,v 1.13 2014/06/23 10:43:25 shm Exp $");
#endif
#endif /* LIBC_SCCS && not lint */

#include "namespace.h"
#include <sys/types.h>

#include <assert.h>
#include <bm.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

#ifdef __weak_alias
__weak_alias(bm_comp,_bm_comp)
__weak_alias(bm_exec,_bm_exec)
__weak_alias(bm_free,_bm_free)
#endif

/* 
 * XXX
 * The default frequency table starts at 99 and counts down.  The default
 * table should probably be oriented toward text, and will necessarily be
 * locale specific.  This one is for English.  It was derived from the
 * OSF/1 and 4.4BSD formatted and unformatted manual pages, and about 100Mb
 * of email and random text.  Change it if you can find something better.
 */
static u_char const freq_def[256] = {
         0,  0,  0,  0,  0,  0,  0,  0,
         0, 77, 90,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
        99, 28, 42, 27, 16, 14, 20, 51,
        66, 65, 59, 24, 75, 76, 84, 56,
        72, 74, 64, 55, 54, 47, 41, 37,
        44, 61, 70, 43, 23, 53, 49, 22,
        33, 58, 40, 46, 45, 57, 60, 26,
        30, 63, 21, 12, 32, 50, 38, 39,
        34, 11, 48, 67, 62, 35, 15, 29,
        71, 18,  9, 17, 25, 13, 10, 52,
        36, 95, 78, 86, 87, 98, 82, 80,
        88, 94, 19, 68, 89, 83, 93, 96,
        81,  7, 91, 92, 97, 85, 69, 73,
        31, 79,  8,  5,  4,  6,  3,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,
};

bm_pat *
bm_comp(u_char const *pb, size_t len, u_char const *freq)
{
        u_char const *pe, *p;
        size_t *d, r;
        int j;
        int sv_errno;
        bm_pat *pat;

        _DIAGASSERT(pb != NULL);
        /* freq may be NULL */

        if (len == 0) {
                errno = EINVAL;
                return (NULL);
        }
        if ((pat = malloc(sizeof(*pat))) == NULL)
                return (NULL);
        pat->pat = NULL;
        pat->delta = NULL;

        pat->patlen = len;                      /* copy pattern */
        if ((pat->pat = malloc(pat->patlen)) == NULL)
                goto mem;
        memcpy(pat->pat, pb, pat->patlen);
                                                /* get skip delta */
        if ((pat->delta = malloc(256 * sizeof(*d))) == NULL)
                goto mem;
        for (j = 0, d = pat->delta; j < 256; j++)
                d[j] = pat->patlen;
        for (pe = pb + pat->patlen - 1; pb <= pe; pb++)
                d[*pb] = pe - pb;

        if (freq == NULL)                       /* default freq table */
                freq = freq_def;
        r = 0;                                  /* get guard */
        for (pb = pat->pat, pe = pb + pat->patlen - 1; pb < pe; pb++)
                if (freq[*pb] < freq[pat->pat[r]])
                        r = pb - pat->pat;
        pat->rarec = pat->pat[r];
        pat->rareoff = r - (pat->patlen - 1);

                                                /* get md2 shift */
        for (pe = pat->pat + pat->patlen - 1, p = pe - 1; p >= pat->pat; p--)
                if (*p == *pe)
                        break;

        /* *p is first leftward reoccurrence of *pe */
        pat->md2 = pe - p;
        return (pat);

mem:    sv_errno = errno;
        bm_free(pat);
        errno = sv_errno;
        return (NULL);
}

void
bm_free(bm_pat *pat)
{

        _DIAGASSERT(pat != NULL);

        free(pat->pat);
        free(pat->delta);
        free(pat);
}

u_char *
bm_exec(bm_pat *pat, u_char *base, size_t n)
{
        u_char *e, *ep, *p, *q, *s;
        size_t *d0, k, md2, n1, ro;
        int rc;

        _DIAGASSERT(pat != NULL);
        _DIAGASSERT(base != NULL);

        if (n == 0)
                return (NULL);

        d0 = pat->delta;
        n1 = pat->patlen - 1;
        md2 = pat->md2;
        ro = pat->rareoff;
        rc = pat->rarec;
        ep = pat->pat + pat->patlen - 1;
        s = base + (pat->patlen - 1);

        /* fast loop up to n - 3 * patlen */
        e = base + n - 3 * pat->patlen;
        while (s < e) {
                k = d0[*s];             /* ufast skip loop */
                while (k && s < e) {
                        k = d0[*(s += k)];
                        k = d0[*(s += k)];
                }
                if (s >= e)
                        break;
                if (s[ro] != rc)        /* guard test */
                        goto mismatch1;
                                        /* fwd match */
                for (p = pat->pat, q = s - n1; p < ep;)
                        if (*q++ != *p++)
                                goto mismatch1;
                return (s - n1);

mismatch1:      s += md2;               /* md2 shift */
        }

        /* slow loop up to end */
        e = base + n;
        while (s < e) {
                s += d0[*s];            /* step */
                if (s >= e)
                        break;
                if (s[ro] != rc)        /* guard test */
                        goto mismatch2;
                                        /* fwd match */
                for (p = pat->pat, q = s - n1; p <= ep;)
                        if (*q++ != *p++)
                                goto mismatch2;
                return (s - n1);

mismatch2:      s += md2;               /* md2 shift */
        }

        return (NULL);
}