[FFmpeg-devel] [PATCH 5/5] all: fix enum definition for large values

Michael Niedermayer michael at niedermayer.cc
Sat Oct 24 20:58:18 CEST 2015

On Sat, Oct 24, 2015 at 02:41:59PM -0400, Ganesh Ajjanagadde wrote:
> On Sat, Oct 24, 2015 at 2:33 PM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> > On Sat, Oct 24, 2015 at 09:29:23AM -0400, Ganesh Ajjanagadde wrote:
> >> ISO C restricts enumerator values to the range of int. Thus (for instance) 0x80000000
> >> unfortunately does not work, and throws a warning with -Wpedantic on
> >> clang 3.7.
> >>
> >> This fixes such errors by explicitly casting as an int, doing the
> >> desired unsigned to signed conversion. This method works on all current
> >> architectures. Tested with FATE.
> >>
> >> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> >
> > Simply changing the values to signed is not correct / not sufficient
> > the code assumes that they are unsigned
> enums are ints (and hence signed).

this is not true (though thats off topic but you seemed interrested in
the C spec) Enumeration specifiers
4 Each enumerated type shall be compatible with char, a signed integer type, or an
  unsigned integer type. The choice of type is implementation-defined,110) but shall be
  capable of representing the values of all the members of the enumeration. The
  enumerated type is incomplete until after the } that terminates the list of enumerator

so a enum type can be almost anything the implementation likes it to
be. 2 enums dont even need to be using the same type and this is not
just specification talk, gcc does this actually, for example it will
use (u)int64 as type when things dont fit in an (unsigned) int
also on at least some embeded platforms gcc will use shorts
for enums that fit in a short int (no i dont know which exactly but
i read about people stumbling into this so it must happen on some

> I doubt code assumed that they are
> unsigned. If code depended on these being unsigned constants, then
> there is no way of placing them in an enum. Are you fine with a macro,
> or do you prefer a static const style? Generally, it seems like FFmpeg
> prefers the macro method for defining such constants/flags.

if have no preferrance for anything beyond the code working

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
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even the very wise cannot see all ends. -- Gandalf
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