Re: [iproute PATCH v3 6/6] misc/ifstat: simplify unsigned value comparison

On Fri, Jun 24, 2016 at 09:20:32AM +0000, David Laight wrote:

From: Phil Sutter

quoted

Sent: 23 June 2016 18:34

By directly comparing the value of both unsigned variables, casting to
signed becomes unnecessary.

This also fixes for compiling with older versions of gcc (at least
<=3.4.6) which emit the following warning:

| ifstat.c: In function `update_db':
| ifstat.c:542: warning: comparison is always false due to limited range of data type

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 misc/ifstat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/misc/ifstat.c b/misc/ifstat.c
index abbb4e732fcef..9a44da487599e 100644
--- a/misc/ifstat.c
+++ b/misc/ifstat.c

@@ -539,7 +539,7 @@ static void update_db(int interval)
 				int i;

 				for (i = 0; i < MAXS; i++) {
-					if ((long)(h1->ival[i] - n->ival[i]) < 0) {
+					if (h1->ival[i] < n->ival[i]) {
 						memset(n->ival, 0, sizeof(n->ival));
 						break;

That isn't the same check.
The original code is using modulo arithmetic.

Oh, right! The code behaves differently if h1->ival[i] is close to
ULONG_MAX and n->ival[i] is very small. Though I don't see where this
becomes relevant. Am I missing another scenario?

Thanks, Phil