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

From	Julia Lawall <julia.lawall@lip6.fr>
Newsgroups	linux.kernel
Subject	Re: [Outreachy kernel] [PATCH v2 2/7] staging: most: Using macro DIV_ROUND_UP
Date	2017-02-22 12:40 +0100
Message-ID	<tdDr5-YS-33@gated-at.bofh.it> (permalink)
References	<tdBfz-7R6-11@gated-at.bofh.it> <tdBpf-7UW-9@gated-at.bofh.it> <tdDr5-YS-35@gated-at.bofh.it>
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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)
>       >                  return DBR_SIZE; /* out of memory */
>       >
>       >          for (i = 0; i < DBR_MAP_SIZE; i++) {
>       > -                u32 const blocks = (size + DBR_BLOCK_SIZE -
>       1) / DBR_BLOCK_SIZE;
>       > +                u32 const blocks = DIV_ROUND_UP(size,
>       DBR_BLOCK_SIZE);
>       >                  u32 mask = ~((~(u32)0) << blocks);
>
>       Totally unrelated to DIV_ROUND_UP, would this code be a
>       candidate for
>       GENMASK?
>
>  
>       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

>
>  
>
>       julia
>
>       >
>       >                  do {
>       > @@ -137,7 +138,7 @@ static int alloc_dbr(u16 size)
>       >  static void free_dbr(int offs, int size)
>       >  {
>       >          int block_idx = offs / DBR_BLOCK_SIZE;
>       > -        u32 const blocks = (size + DBR_BLOCK_SIZE - 1) /
>       DBR_BLOCK_SIZE;
>       > +        u32 const blocks = DIV_ROUND_UP(size,
>       DBR_BLOCK_SIZE);
>       >          u32 mask = ~((~(u32)0) << blocks);
>       >
>       >          mask <<= block_idx % 32;
>       > --
>       > 2.7.4
>       >
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[PATCH v2 2/7] staging: most: Using macro DIV_ROUND_UP simran singhal <singhalsimran0@gmail.com> - 2017-02-22 10:20 +0100
  Re: [Outreachy kernel] [PATCH v2 2/7] staging: most: Using macro  DIV_ROUND_UP Julia Lawall <julia.lawall@lip6.fr> - 2017-02-22 10:30 +0100
    Re: [Outreachy kernel] [PATCH v2 2/7] staging: most: Using macro  DIV_ROUND_UP Joe Perches <joe@perches.com> - 2017-02-22 11:10 +0100
    Re: [Outreachy kernel] [PATCH v2 2/7] staging: most: Using macro  DIV_ROUND_UP Julia Lawall <julia.lawall@lip6.fr> - 2017-02-22 12:40 +0100

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