[PATCH v1] [media] v4l2-common: fix aligned value calculation

[PATCH v1] [media] v4l2-common: fix aligned value calculation

[Jean-Christophe Trotin]

Correct the calculation of the rounding to nearest aligned value in
the clamp_align() function. For example, clamp_align(1277, 1, 9600, 2)
returns 1276, while it should return 1280.

Signed-off-by: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
---
 drivers/media/v4l2-core/v4l2-common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
index 57cfe26a..2970ce7 100644
--- a/drivers/media/v4l2-core/v4l2-common.c
+++ b/drivers/media/v4l2-core/v4l2-common.c
@@ -315,7 +315,7 @@ static unsigned int clamp_align(unsigned int x, unsigned int min,
 
 	/* Round to nearest aligned value */
 	if (align)
-		x = (x + (1 << (align - 1))) & mask;
+		x = (x + ((1 << align) - 1)) & mask;
 
 	return x;
 }
-- 
1.9.1

Re: [PATCH v1] [media] v4l2-common: fix aligned value calculation

[Sakari Ailus]

Hi Jean-Christophe,

On Fri, Dec 16, 2016 at 02:32:15PM +0100, Jean-Christophe Trotin wrote:
> Correct the calculation of the rounding to nearest aligned value in
> the clamp_align() function. For example, clamp_align(1277, 1, 9600, 2)
> returns 1276, while it should return 1280.

Why should the function return 1280 instead of 1276, which is closer to
1277?

> 
> Signed-off-by: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
> ---
>  drivers/media/v4l2-core/v4l2-common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 57cfe26a..2970ce7 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -315,7 +315,7 @@ static unsigned int clamp_align(unsigned int x, unsigned int min,
>  
>  	/* Round to nearest aligned value */
>  	if (align)
> -		x = (x + (1 << (align - 1))) & mask;
> +		x = (x + ((1 << align) - 1)) & mask;
>  
>  	return x;
>  }

-- 
Regards,

Sakari Ailus
e-mail: sakari.ailus@iki.fi	XMPP: sailus@retiisi.org.uk

Re: [PATCH v1] [media] v4l2-common: fix aligned value calculation

[Jean Christophe TROTIN]

Hi Sakari,

Thank you for your answer.
You're right: the modification that I proposed, is not correct (I misunderstood 
the aim of the function); the current clamp_align() is correct and doesn't need 
any modification.
Thus, the patch that I sent, must be ignored.
Sorry for the disruption.

Regards,
Jean-Christophe.


On 12/16/2016 02:56 PM, Sakari Ailus wrote:
> Hi Jean-Christophe,
>
> On Fri, Dec 16, 2016 at 02:32:15PM +0100, Jean-Christophe Trotin wrote:
>> Correct the calculation of the rounding to nearest aligned value in
>> the clamp_align() function. For example, clamp_align(1277, 1, 9600, 2)
>> returns 1276, while it should return 1280.
>
> Why should the function return 1280 instead of 1276, which is closer to
> 1277?
>
>>
>> Signed-off-by: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
>> ---
>>  drivers/media/v4l2-core/v4l2-common.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
>> index 57cfe26a..2970ce7 100644
>> --- a/drivers/media/v4l2-core/v4l2-common.c
>> +++ b/drivers/media/v4l2-core/v4l2-common.c
>> @@ -315,7 +315,7 @@ static unsigned int clamp_align(unsigned int x, unsigned int min,
>>
>>  	/* Round to nearest aligned value */
>>  	if (align)
>> -		x = (x + (1 << (align - 1))) & mask;
>> +		x = (x + ((1 << align) - 1)) & mask;
>>
>>  	return x;
>>  }
>