[Mesa-dev] [PATCH] util/macros: Simplify DIV_ROUND_UP() definition

[Nanley Chery]

On Thu, Dec 17, 2015 at 11:25 AM, Matt Turner <mattst88 at gmail.com> wrote:

> On Thu, Dec 17, 2015 at 11:04 AM, Nanley Chery <nanleychery at gmail.com>
> wrote:
> > On Thu, Dec 17, 2015 at 12:05:46PM +0100, Glenn Kennard wrote:
> >> On Wed, 16 Dec 2015 20:57:51 +0100, Nanley Chery <nanleychery at gmail.com>
> wrote:
> >>
> >> >From: Nanley Chery <nanley.g.chery at intel.com>
> >> >
> >> >Commit 64880d073ab21ae1abad0c049ea2d6a1169a3cfa consolidated two
> >> >DIV_ROUND_UP() definitions to one, but chose the more
> >> >compute-intensive version in the process. Use the simpler version
> >> >instead. Reduces .text size by 1360 bytes.
> >> >
> >> >Output of `size lib/i965_dri.so`:
> >> >      text    data     bss     dec     hex filename
> >> >   7850440  219264   27240 8096944  7b8cb0 lib/i965_dri.so (before)
> >> >   7849080  219264   27240 8095584  7b8760 lib/i965_dri.so (after)
> >> >
> >> >Cc: Axel Davy <axel.davy at ens.fr>
> >> >Signed-off-by: Nanley Chery <nanley.g.chery at intel.com>
> >> >---
> >> > src/util/macros.h | 2 +-
> >> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >> >
> >> >diff --git a/src/util/macros.h b/src/util/macros.h
> >> >index 0c8958f..53a98a0 100644
> >> >--- a/src/util/macros.h
> >> >+++ b/src/util/macros.h
> >> >@@ -211,6 +211,6 @@ do {                       \
> >> > #endif
> >> >/** Compute ceiling of integer quotient of A divided by B. */
> >> >-#define DIV_ROUND_UP( A, B )  ( (A) % (B) == 0 ? (A)/(B) : (A)/(B)+1 )
> >> >+#define DIV_ROUND_UP(A, B)  (((A) + (B) - 1) / (B))
> >> >#endif /* UTIL_MACROS_H */
> >>
> >> I'll point out that these are not equivalent, one can overflow and the
> other doesn't. You
> >> probably want to check if the call sites have sufficient checks for
> that before
> >> substituting one for the other.
> >>
> >
> > Good point. As I mentioned in another email, I'll leave the current
> > macro untouched.
>
>
The other email I referenced unfortunately didn't make it to the list due
email client
issues.


> I think the chances of us relying on overflow behavior are exceedingly
> small, and nearly all uses of DIV_ROUND_UP are in the i965 driver. I
> think it's sufficiently safe to go ahead with the patch (but I am
> still interested to know about your compiler and CFLAGS).
>

My error was that I forgot to remove --enable-debug and add -02. After
making those
changes, my binary size also increases but by ~1.1k. Another implementation
which
avoids overflow increases the binary size by 2 bytes.

Correct me if I'm wrong, but aligning w/ the kernel implementation (or
changing the
current definition for that matter) seems like a regression more than an
improvement.

Thanks,
Nanley
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