2020-04-19 10:12:12

by Oscar Carter

Subject: [PATCH] staging: vt6656: Use fls instead of for loop in vnt_update_top_rates

Replace the for loops of the vnt_update_top_rates function by the fls
function.

The purpose of the two for loops is to find the most significant bit set
in a range of bits. So, they can be replace by the fls function (find
last set) with a previous mask to define the range.

This way avoid the iteration over unnecessary for loops.

The header "linux/bits.h" can be remove as it is included in the header
"linux/bitops.h".

Signed-off-by: Oscar Carter <[email protected]>
---
drivers/staging/vt6656/card.c | 28 ++++++----------------------
1 file changed, 6 insertions(+), 22 deletions(-)

diff --git a/drivers/staging/vt6656/card.c b/drivers/staging/vt6656/card.c
index 9bd37e57c727..952a7726fdd3 100644
--- a/drivers/staging/vt6656/card.c
+++ b/drivers/staging/vt6656/card.c
@@ -26,7 +26,7 @@
*
*/

-#include <linux/bits.h>
+#include <linux/bitops.h>
#include "device.h"
#include "card.h"
#include "baseband.h"
@@ -223,29 +223,13 @@ void vnt_update_ifs(struct vnt_private *priv)

void vnt_update_top_rates(struct vnt_private *priv)
{
- u8 top_ofdm = RATE_24M, top_cck = RATE_1M;
- u8 i;
+ int pos;

- /*Determines the highest basic rate.*/
- for (i = RATE_54M; i >= RATE_6M; i--) {
- if (priv->basic_rates & (u16)(1 << i)) {
- top_ofdm = i;
- break;
- }
- }
-
- priv->top_ofdm_basic_rate = top_ofdm;
-
- for (i = RATE_11M;; i--) {
- if (priv->basic_rates & (u16)(1 << i)) {
- top_cck = i;
- break;
- }
- if (i == RATE_1M)
- break;
- }
+ pos = fls(priv->basic_rates & GENMASK(RATE_54M, RATE_6M));
+ priv->top_ofdm_basic_rate = pos ? pos-- : RATE_24M;

- priv->top_cck_basic_rate = top_cck;
+ pos = fls(priv->basic_rates & GENMASK(RATE_11M, RATE_1M));
+ priv->top_cck_basic_rate = pos ? pos-- : RATE_1M;
}

int vnt_ofdm_min_rate(struct vnt_private *priv)
--
2.20.1

2020-04-20 12:16:40

by Dan Carpenter

Subject: Re: [PATCH] staging: vt6656: Use fls instead of for loop in vnt_update_top_rates

On Sun, Apr 19, 2020 at 12:09:21PM +0200, Oscar Carter wrote:
> - for (i = RATE_11M;; i--) {
> - if (priv->basic_rates & (u16)(1 << i)) {
> - top_cck = i;
> - break;
> - }
> - if (i == RATE_1M)
> - break;
> - }
> + pos = fls(priv->basic_rates & GENMASK(RATE_54M, RATE_6M));
> + priv->top_ofdm_basic_rate = pos ? pos-- : RATE_24M;
^^^^^
Argh... Come on. I don't want to have to break out the C standard to
see if this is defined behavior and where the sequence points are. A
pre-op would be clear but the most clear thing is to write it like this:

priv->top_ofdm_basic_rate = pos ? (pos - 1) : RATE_24M;


>
> - priv->top_cck_basic_rate = top_cck;
> + pos = fls(priv->basic_rates & GENMASK(RATE_11M, RATE_1M));
> + priv->top_cck_basic_rate = pos ? pos-- : RATE_1M;
^^^^^
Same.

regards,
dan carpenter

2020-04-20 15:18:30

by Oscar Carter

Subject: Re: [PATCH] staging: vt6656: Use fls instead of for loop in vnt_update_top_rates

On Mon, Apr 20, 2020 at 03:10:59PM +0300, Dan Carpenter wrote:
> On Sun, Apr 19, 2020 at 12:09:21PM +0200, Oscar Carter wrote:
> > - for (i = RATE_11M;; i--) {
> > - if (priv->basic_rates & (u16)(1 << i)) {
> > - top_cck = i;
> > - break;
> > - }
> > - if (i == RATE_1M)
> > - break;
> > - }
> > + pos = fls(priv->basic_rates & GENMASK(RATE_54M, RATE_6M));
> > + priv->top_ofdm_basic_rate = pos ? pos-- : RATE_24M;
> ^^^^^
> Argh... Come on. I don't want to have to break out the C standard to
> see if this is defined behavior and where the sequence points are. A
> pre-op would be clear but the most clear thing is to write it like this:
>
> priv->top_ofdm_basic_rate = pos ? (pos - 1) : RATE_24M;
>
Ok, I do the modification as you suggested and resend a new version.
>
> >
> > - priv->top_cck_basic_rate = top_cck;
> > + pos = fls(priv->basic_rates & GENMASK(RATE_11M, RATE_1M));
> > + priv->top_cck_basic_rate = pos ? pos-- : RATE_1M;
> ^^^^^
> Same.
>
> regards,
> dan carpenter
>
thanks,
oscar carter