Re: [Outreachy kernel] [PATCH v2 2/7] staging: most: Using macro DIV_ROUND_UP

[Julia Lawall]

On Wed, 22 Feb 2017, SIMRAN SINGHAL wrote:

>
>
> On Wednesday, February 22, 2017 at 2:57:17 PM UTC+5:30, Julia Lawall wrote:
>       > @@ -117,7 +118,7 @@ static int alloc_dbr(u16 size)
>       > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂreturn DBR_SIZE; /* out of memory */
>       >
>       > ÂÂÂÂÂÂÂÂÂfor (i = 0; i < DBR_MAP_SIZE; i++) {
>       > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂu32 const blocks = (size + DBR_BLOCK_SIZE -
>       1) / DBR_BLOCK_SIZE;
>       > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂu32 const blocks = DIV_ROUND_UP(size,
>       DBR_BLOCK_SIZE);
>       > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂu32 mask = ~((~(u32)0) << blocks);
>
>       Totally unrelated to DIV_ROUND_UP, would this code be a
>       candidate for
>       GENMASK?
>
> Â
>       Not sure, what you are trying to say.

There was a discussion on the list recently about GENMASK, which allows to
create a mask containing a sequence of 1s, like 000011110000.  It looks
like that is what is being done here, because ~0 is 11111111 and then it
ie being shifted left and all the bits inverted.  But Joe had another
suggestion.  One could double check that his suggestion gives the right
result.

julia

>
> Â
>
>       julia
>
>       >
>       > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂdo {
>       > @@ -137,7 +138,7 @@ static int alloc_dbr(u16 size)
>       > Âstatic void free_dbr(int offs, int size)
>       > Â{
>       > ÂÂÂÂÂÂÂÂÂint block_idx = offs / DBR_BLOCK_SIZE;
>       > -ÂÂÂÂÂÂÂÂu32 const blocks = (size + DBR_BLOCK_SIZE - 1) /
>       DBR_BLOCK_SIZE;
>       > +ÂÂÂÂÂÂÂÂu32 const blocks = DIV_ROUND_UP(size,
>       DBR_BLOCK_SIZE);
>       > ÂÂÂÂÂÂÂÂÂu32 mask = ~((~(u32)0) << blocks);
>       >
>       > ÂÂÂÂÂÂÂÂÂmask <<= block_idx % 32;
>       > --
>       > 2.7.4
>       >
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