No need for buffers t0, t1 here. This way we only have to step/move the
current position instead of the total bytes left as well as both source
and destination position.
Always swap an even number of bytes by clearing the length's last bit
and never write past it.
The , operator can be used safely here as the order of execution is
irrelevant (in case it's not guaranteed).
POSIX leaves treatment of the last odd byte unspecified but we don't
touch it at all so why not documenting this behaviour?
Feedback? Comments?
Index: swab.c
===================================================================
RCS file: /cvs/src/lib/libc/string/swab.c,v
retrieving revision 1.9
diff -u -p -r1.9 swab.c
--- swab.c 11 Dec 2014 23:05:38 -0000 1.9
+++ swab.c 5 Jul 2017 14:12:34 -0000
@@ -21,15 +21,8 @@ swab(const void *__restrict from, void *
{
const unsigned char *src = from;
unsigned char *dst = to;
- unsigned char t0, t1;
+ ssize_t i;
- while (len > 1) {
- t0 = src[0];
- t1 = src[1];
- dst[0] = t1;
- dst[1] = t0;
- src += 2;
- dst += 2;
- len -= 2;
- }
+ for (i = 0; i < (len & ~1) - 1; i += 2)
+ dst[i] = src[i + 1], dst[i + 1] = src[i];
}
Index: swab.3
===================================================================
RCS file: /cvs/src/lib/libc/string/swab.3,v
retrieving revision 1.9
diff -u -p -r1.9 swab.3
--- swab.3 12 Dec 2014 20:06:13 -0000 1.9
+++ swab.3 5 Jul 2017 14:12:34 -0000
@@ -57,7 +57,9 @@ If
is zero or less,
.Nm
does nothing.
-If it is odd, what happens to the last byte is unspecified.
+If it is odd,
+.Fa len Ns \-1
+bytes are swapped and the last byte is ignored.
If
.Fa src
and
