/*
 * Copyright (c) 1987, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 *
 * $FreeBSD: src/sys/libkern/bcmp.c,v 1.6 1999/08/28 00:46:31 peter Exp $
 * $DragonFly: src/sys/libkern/bcmp.c,v 1.4 2005/01/04 05:27:47 cpressey Exp $
 */

#include <string.h>
#include <machine/endian.h>

typedef const void              *cvp;
typedef const unsigned char     *ustring;
typedef unsigned long           ul;
typedef const unsigned long     *culp;

/*
 * bcmp -- vax cmpc3 instruction
 */
int
bcmp(const void *b1, const void *b2, size_t length)
{
#if BYTE_ORDER == LITTLE_ENDIAN
        /*
         * The following code is endian specific.  Changing it from
         * little-endian to big-endian is fairly trivial, but making
         * it do both is more difficult.
         *
         * Note that this code will reference the entire longword which
         * includes the final byte to compare.  I don't believe this is
         * a problem since AFAIK, objects are not protected at smaller
         * than longword boundaries.
         */
        int     shl, shr, len = length;
        ustring p1 = b1, p2 = b2;
        ul      va, vb;

        if (len == 0)
                return (0);

        /*
         * align p1 to a longword boundary
         */
        while ((long)p1 & (sizeof(long) - 1)) {
                if (*p1++ != *p2++)
                        return (1);
                if (--len <= 0)
                        return (0);
        }

        /*
         * align p2 to longword boundary and calculate the shift required to
         * align p1 and p2
         */
        shr = (long)p2 & (sizeof(long) - 1);
        if (shr != 0) {
                p2 -= shr;                      /* p2 now longword aligned */
                shr <<= 3;                      /* offset in bits */
                shl = (sizeof(long) << 3) - shr;

                va = *(culp)p2;
                p2 += sizeof(long);

                while ((len -= sizeof(long)) >= 0) {
                        vb = *(culp)p2;
                        p2 += sizeof(long);
                        if (*(culp)p1 != (va >> shr | vb << shl))
                                return (1);
                        p1 += sizeof(long);
                        va = vb;
                }
                /*
                 * At this point, len is between -sizeof(long) and -1,
                 * representing 0 .. sizeof(long)-1 bytes remaining.
                 */
                if (!(len += sizeof(long)))
                        return (0);

                len <<= 3;              /* remaining length in bits */
                /*
                 * The following is similar to the `if' condition
                 * inside the above while loop.  The ?: is necessary
                 * to avoid accessing the longword after the longword
                 * containing the last byte to be compared.
                 */
                return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
                    *(culp)p1) & ((1L << len) - 1)) != 0);
        } else {
                /* p1 and p2 have common alignment so no shifting needed */
                while ((len -= sizeof(long)) >= 0) {
                        if (*(culp)p1 != *(culp)p2)
                                return (1);
                        p1 += sizeof(long);
                        p2 += sizeof(long);
                }

                /*
                 * At this point, len is between -sizeof(long) and -1,
                 * representing 0 .. sizeof(long)-1 bytes remaining.
                 */
                if (!(len += sizeof(long)))
                        return (0);

                return (((*(culp)p1 ^ *(culp)p2)
                         & ((1L << (len << 3)) - 1)) != 0);
        }
#else
        char *p1, *p2;

        if (length == 0)
                return(0);
        p1 = (char *)b1;
        p2 = (char *)b2;
        do
                if (*p1++ != *p2++)
                        break;
        while (--length);
        return(length);
#endif
}