/*      $NetBSD: swab.c,v 1.20 2022/12/28 15:34:19 riastradh Exp $      */


/*-
* Copyright (c) 2022 The NetBSD Foundation, Inc.
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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)
__RCSID("$NetBSD: swab.c,v 1.20 2022/12/28 15:34:19 riastradh Exp $");
#endif

#include <assert.h>
#include <unistd.h>

void
swab(const void *__restrict src, void *__restrict dst, ssize_t nbytes)
{
       const char *p = src;
       char *q = dst;
       size_t n;

       _DIAGASSERT(src != NULL);
       _DIAGASSERT(dst != NULL);

       if (nbytes <= 1)
               return;

       /*
        * Round nbytes/2 down; we ignore the last byte altogether if
        * nbytes is odd.  This way, if the destination array is
        * uninitialized, sanitizers will recognize the last byte as
        * still uninitialized and flag it as undefined.
        */
       for (n = nbytes/2; n --> 0; p += 2, q += 2) {
               /*
                * According to POSIX (2018), the behaviour is
                * undefined if src and dst overlap.  However, there
                * are uses in-tree (xsrc/external/mit/xfwp/dist/io.c)
                * that rely on swab(ptr, ptr, n) to do the swabbing
                * in-place.  So make sure this works if src == dst.
                */
               const char p0 = p[0], p1 = p[1];

               q[0] = p1;
               q[1] = p0;
       }
}