update swab() to match the current posix definition. "rationale: none."

rewrite the function to be simpler as well. the compiler can unroll the
loop for us if necessary.
ok schwarze

src/include/unistd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: unistd.h,v 1.95 2014/12/08 20:39:56 tedu Exp $ */
+/*	$OpenBSD: unistd.h,v 1.96 2014/12/11 23:05:38 tedu Exp $ */
 /*	$NetBSD: unistd.h,v 1.26.4.1 1996/05/28 02:31:51 mrg Exp $	*/
 
 /*-
@@ -424,7 +424,7 @@ char	*mktemp(char *);
 int	 nice(int);
 int	 setregid(gid_t, gid_t);
 int	 setreuid(uid_t, uid_t);
-void	 swab(const void *, void *, size_t);
+void	 swab(const void *__restrict, void *__restrict, ssize_t);
 void	 sync(void);
 int	 truncate(const char *, off_t);
 useconds_t	 ualarm(useconds_t, useconds_t);

src/lib/libc/string/swab.c

@@ -1,61 +1,35 @@
-/*	$OpenBSD: swab.c,v 1.8 2008/03/15 21:54:09 ray Exp $ */
+/*	$OpenBSD: swab.c,v 1.9 2014/12/11 23:05:38 tedu Exp $ */
 /*
- * Copyright (c) 1988 Regents of the University of California.
- * All rights reserved.
+ * Copyright (c) 2014 Ted Unangst <tedu@openbsd.org>
  *
- * This code is derived from software contributed to Berkeley by
- * Jeffrey Mogul.
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
  *
- * 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.
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
-
 #include <unistd.h>
 
 void
-swab(const void *from, void *to, size_t len)
+swab(const void *__restrict from, void *__restrict to, ssize_t len)
 {
-	size_t n;
-	char *fp, *tp;
-	char temp;
+	const unsigned char *src = from;
+	unsigned char *dst = to;
+	unsigned char t0, t1;
 
-	n = (len / 2) + 1;
-	fp = (char *)from;
-	tp = (char *)to;
-#define	STEP do {	\
-	temp = *fp++;	\
-	*tp++ = *fp++;	\
-	*tp++ = temp;	\
-} while (0)
-	/* round to multiple of 8 */
-	while ((--n) & 07)
-		STEP;
-	n >>= 3;
-	if (n == 0)
-		return;
-	while (n-- != 0) {
-		STEP; STEP; STEP; STEP;
-		STEP; STEP; STEP; STEP;
+	while (len > 1) {
+		t0 = src[0];
+		t1 = src[1];
+		dst[0] = t1;
+		dst[1] = t0;
+		src += 2;
+		dst += 2;
+		len -= 2;
 	}
 }