Re: [PATCH 4/9v2] usb: host: ehci.h: fix single statement macros

From: Sergei Shtylyov
Date: Thu Dec 10 2015 - 12:47:16 EST

On 12/10/2015 08:40 PM, Geyslan G. Bem wrote:

Don't use the 'do {} while (0)' wrapper in a single statement macro.

Caught by checkpatch: "WARNING: Single statement macros should not
use a do {} while (0) loop"

Signed-off-by: Geyslan G. Bem <geyslan@xxxxxxxxx>
drivers/usb/host/ehci.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index cfeebd8..945000a 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -244,9 +244,9 @@ struct ehci_hcd { /* one per
controller */
/* irq statistics */
struct ehci_stats stats;
-# define COUNT(x) do { (x)++; } while (0)
+# define COUNT(x) ((x)++)
-# define COUNT(x) do {} while (0)
+# define COUNT(x) ((void) 0)

Why not just empty #define?

Indeed. I'll change it.
Tks Sergei.

Since COUNT is not used to return the empty #define is ok. Another way
is to use #define COUNT(x) (0) to get a 0 when necessary to read

Just 0, no parens please.

Ok, no parens, since there's no evaluation.

It's because the literals don't need parens at all.

Then my change is:

-# define COUNT(x) do { (x)++; } while (0)
+# define COUNT(x) (++(x))
-# define COUNT(x) do {} while (0)
+# define COUNT(x) 0

Pre-increment allowing to return the updated x.

Why if there was a post-increment before?

There's nothing wrong with post-increment. The pre one would be
necessary if using return.

Maybe it was intended to return the old value? :-)

Anyway, this talk is quite pointless since the macro didn't return any
value anyway.
You're sure, there's no use anywhere of the return of that macro indeed.

*do* {} *while* (0) just couldn't return any value, it's not just a compound statement which gcc indeed allows to be evaluated.

Sending v2 soon.

MBR, Sergei

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