linux-kernel - Re: [PATCH v7 6/8] math.h Add macros to round to closest specified power of 2

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Date: Sat, 11 May 2024 22:56:31 +0530
From: Devarsh Thakkar <devarsht@...com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC: <mchehab@...nel.org>, <hverkuil-cisco@...all.nl>,
        <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <benjamin.gaignard@...labora.com>, <sebastian.fricke@...labora.com>,
        <akpm@...ux-foundation.org>, <gregkh@...uxfoundation.org>,
        <adobriyan@...il.com>, <jani.nikula@...el.com>,
        <p.zabel@...gutronix.de>, <airlied@...il.com>, <daniel@...ll.ch>,
        <dri-devel@...ts.freedesktop.org>, <laurent.pinchart@...asonboard.com>,
        <praneeth@...com>, <nm@...com>, <vigneshr@...com>, <a-bhatia1@...com>,
        <j-luthra@...com>, <b-brnich@...com>, <detheridge@...com>,
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        <nicolas@...fresne.ca>
Subject: Re: [PATCH v7 6/8] math.h Add macros to round to closest specified
 power of 2

Hi Andy,

Thanks for the quick review.

On 10/05/24 20:31, Andy Shevchenko wrote:
> On Fri, May 10, 2024 at 12:09:52AM +0530, Devarsh Thakkar wrote:
>> Add macros to round to nearest specified power of 2.
> 
> This is not what they are doing. For the above we already have macros defined.
> 

Sorry I did not understand this comment, if you are talking about
existing macros round_up & round_down they either round "up" and round
"down" to specified power of 2 as specified here [1].
whereas the macros introduced in this patch round to "nearest" specified
power of 2.

>> Two macros are added :
> 
> (Yes, after I wrapped to comment this line looks better on its own,
>  so whatever will be the first sentence, this line should be separated
>  from.)
> 

Agreed.

>> round_closest_up and round_closest_down which round up to nearest multiple
> 
> round_closest_up() and round_closest_down()
> 
> 
>> of 2 with a preference to round up or round down respectively if there are
>> two possible nearest values to the given number.
> 
> You should reformulate, because AFAICS there is the crucial difference
> from these and existing round_*_pow_of_two().
> 

In math.h, we already have round_up/round_down macros which rounded
up/down to next specified power of 2. Then we had the DIV_ROUND_CLOSEST
which used the suffix _CLOSEST to imply the meaning that divided value
will be rounded to nearest/closest int value either by rounding up or
rounding down.

So inspired from naming convention of this macros given developers are
already familiar with them, I used round_closest for specifying the
rounded value to nearest/closest value which can be achieved either by
rounding up/down. And I also wanted user to have finer control for the
scenarios where there are two possible nearest values :

For e.g round(160, 64) can be either 192 and 128 and both are 32 away
from 160.

And that's the reason I went ahead with two macros instead i.e
round_closest_up, round_closest_down so that developers can choose
exactly what they want.

Regards
Devarsh