[FFmpeg-devel] [PATCHv2] all: fix enum definition for large values
Ganesh Ajjanagadde
gajjanag at mit.edu
Thu Oct 29 12:55:00 CET 2015
On Thu, Oct 29, 2015 at 12:29 AM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Wed, Oct 28, 2015 at 07:02:42PM -0400, Ganesh Ajjanagadde wrote:
>> On Wed, Oct 28, 2015 at 3:05 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>> > Hi,
>> >
>> > On Wed, Oct 28, 2015 at 2:46 PM, Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>> > wrote:
>> >>
>> >> On Wed, Oct 28, 2015 at 2:39 PM, Ronald S. Bultje <rsbultje at gmail.com>
>> >> wrote:
>> >> > Hi,
>> >> >
>> >> > On Wed, Oct 28, 2015 at 2:31 PM, Ganesh Ajjanagadde
>> >> > <gajjanagadde at gmail.com>
>> >> > wrote:
>> >> >>
>> >> >> On Wed, Oct 28, 2015 at 11:38 AM, Ronald S. Bultje <rsbultje at gmail.com>
>> >> >> wrote:
>> >> >> > Hi,
>> >> >> >
>> >> >> > On Wed, Oct 28, 2015 at 11:00 AM, Ganesh Ajjanagadde
>> >> >> > <gajjanagadde at gmail.com> wrote:
>> >> >> >>
>> >> >> >> On Wed, Oct 28, 2015 at 10:53 AM, Ronald S. Bultje
>> >> >> >> <rsbultje at gmail.com>
>> >> >> >> wrote:
>> >> >> >> > Hi,
>> >> >> >> >
>> >> >> >> > On Wed, Oct 28, 2015 at 10:48 AM, Ganesh Ajjanagadde
>> >> >> >> > <gajjanagadde at gmail.com> wrote:
>> >> >> >> >>
>> >> >> >> >> On Wed, Oct 28, 2015 at 10:34 AM, Ronald S. Bultje
>> >> >> >> >> <rsbultje at gmail.com>
>> >> >> >> >> wrote:
>> >> >> >> >> > Hi,
>> >> >> >> >> >
>> >> >> >> >> > On Wed, Oct 28, 2015 at 8:20 AM, Ganesh Ajjanagadde
>> >> >> >> >> > <gajjanagadde at gmail.com>
>> >> >> >> >> > wrote:
>> >> >> >> >> >>
>> >> >> >> >> >> On Wed, Oct 28, 2015 at 7:00 AM, Ronald S. Bultje
>> >> >> >> >> >> <rsbultje at gmail.com>
>> >> >> >> >> >> wrote:
>> >> >> >> >> >> > Hi,
>> >> >> >> >> >> >
>> >> >> >> >> >> > On Tue, Oct 27, 2015 at 10:58 PM, Ganesh Ajjanagadde
>> >> >> >> >> >> > <gajjanagadde at gmail.com> wrote:
>> >> >> >> >> >> >>
>> >> >> >> >> >> >> On Tue, Oct 27, 2015 at 10:41 PM, Ronald S. Bultje
>> >> >> >> >> >> >> <rsbultje at gmail.com>
>> >> >> >> >> >> >> wrote:
>> >> >> >> >> >> >> > Hi,
>> >> >> >> >> >> >> >
>> >> >> >> >> >> >> > On Tue, Oct 27, 2015 at 8:53 PM, Ganesh Ajjanagadde
>> >> >> >> >> >> >> > <gajjanagadde at gmail.com>
>> >> >> >> >> >> >> > 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 it by using alternative expressions that
>> >> >> >> >> >> >> >> result
>> >> >> >> >> >> >> >> in
>> >> >> >> >> >> >> >> identical
>> >> >> >> >> >> >> >> values but do not have this issue.
>> >> >> >> >> >> >> >>
>> >> >> >> >> >> >> >> Tested with FATE.
>> >> >> >> >> >> >> >>
>> >> >> >> >> >> >> >> Signed-off-by: Ganesh Ajjanagadde
>> >> >> >> >> >> >> >> <gajjanagadde at gmail.com>
>> >> >> >> >> >> >> >> ---
>> >> >> >> >> >> >> >> libavcodec/dca_syncwords.h | 26
>> >> >> >> >> >> >> >> ++++++++++++--------------
>> >> >> >> >> >> >> >> libavformat/cinedec.c | 2 +-
>> >> >> >> >> >> >> >> libavformat/mov_chan.c | 2 +-
>> >> >> >> >> >> >> >> 3 files changed, 14 insertions(+), 16 deletions(-)
>> >> >> >> >> >> >> >>
>> >> >> >> >> >> >> >> diff --git a/libavcodec/dca_syncwords.h
>> >> >> >> >> >> >> >> b/libavcodec/dca_syncwords.h
>> >> >> >> >> >> >> >> index 3466b6b..6981cb8 100644
>> >> >> >> >> >> >> >> --- a/libavcodec/dca_syncwords.h
>> >> >> >> >> >> >> >> +++ b/libavcodec/dca_syncwords.h
>> >> >> >> >> >> >> >> @@ -19,19 +19,17 @@
>> >> >> >> >> >> >> >> #ifndef AVCODEC_DCA_SYNCWORDS_H
>> >> >> >> >> >> >> >> #define AVCODEC_DCA_SYNCWORDS_H
>> >> >> >> >> >> >> >>
>> >> >> >> >> >> >> >> -enum DCASyncwords {
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_CORE_BE = 0x7FFE8001U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_CORE_LE = 0xFE7F0180U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_CORE_14B_BE = 0x1FFFE800U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_CORE_14B_LE = 0xFF1F00E8U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_XCH = 0x5A5A5A5AU,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_XXCH = 0x47004A03U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_X96 = 0x1D95F262U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_XBR = 0x655E315EU,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_LBR = 0x0A801921U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_XLL = 0x41A29547U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_SUBSTREAM = 0x64582025U,
>> >> >> >> >> >> >> >> - DCA_SYNCWORD_SUBSTREAM_CORE = 0x02B09261U,
>> >> >> >> >> >> >> >> -};
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_CORE_BE
>> >> >> >> >> >> >> >> 0x7FFE8001U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_CORE_LE
>> >> >> >> >> >> >> >> 0xFE7F0180U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_CORE_14B_BE
>> >> >> >> >> >> >> >> 0x1FFFE800U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_CORE_14B_LE
>> >> >> >> >> >> >> >> 0xFF1F00E8U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_XCH
>> >> >> >> >> >> >> >> 0x5A5A5A5AU
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_XXCH
>> >> >> >> >> >> >> >> 0x47004A03U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_X96
>> >> >> >> >> >> >> >> 0x1D95F262U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_XBR
>> >> >> >> >> >> >> >> 0x655E315EU
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_LBR
>> >> >> >> >> >> >> >> 0x0A801921U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_XLL
>> >> >> >> >> >> >> >> 0x41A29547U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_SUBSTREAM
>> >> >> >> >> >> >> >> 0x64582025U
>> >> >> >> >> >> >> >> +#define DCA_SYNCWORD_SUBSTREAM_CORE
>> >> >> >> >> >> >> >> 0x02B09261U
>> >> >> >> >> >> >> >
>> >> >> >> >> >> >> >
>> >> >> >> >> >> >> > This one is fine.
>> >> >> >> >> >> >> >
>> >> >> >> >> >> >> >>
>> >> >> >> >> >> >> >> --- a/libavformat/cinedec.c
>> >> >> >> >> >> >> >> +++ b/libavformat/cinedec.c
>> >> >> >> >> >> >> >> @@ -50,7 +50,7 @@ enum {
>> >> >> >> >> >> >> >> CFA_BAYER = 3, /**< GB/RG */
>> >> >> >> >> >> >> >> CFA_BAYERFLIP = 4, /**< RG/GB */
>> >> >> >> >> >> >> >>
>> >> >> >> >> >> >> >> - CFA_TLGRAY = 0x80000000,
>> >> >> >> >> >> >> >> + CFA_TLGRAY = INT32_MIN,
>> >> >> >> >> >> >> >> CFA_TRGRAY = 0x40000000,
>> >> >> >> >> >> >> >> CFA_BLGRAY = 0x20000000,
>> >> >> >> >> >> >> >> CFA_BRGRAY = 0x10000000
>> >> >> >> >> >> >> >> diff --git a/libavformat/mov_chan.c
>> >> >> >> >> >> >> >> b/libavformat/mov_chan.c
>> >> >> >> >> >> >> >> index a2fa8d6..f6181e2 100644
>> >> >> >> >> >> >> >> --- a/libavformat/mov_chan.c
>> >> >> >> >> >> >> >> +++ b/libavformat/mov_chan.c
>> >> >> >> >> >> >> >> @@ -45,7 +45,7 @@
>> >> >> >> >> >> >> >> * do not specify a particular ordering of
>> >> >> >> >> >> >> >> those
>> >> >> >> >> >> >> >> channels."
>> >> >> >> >> >> >> >> */
>> >> >> >> >> >> >> >> enum MovChannelLayoutTag {
>> >> >> >> >> >> >> >> - MOV_CH_LAYOUT_UNKNOWN = 0xFFFF0000,
>> >> >> >> >> >> >> >> + MOV_CH_LAYOUT_UNKNOWN = -( 1 << 16),
>> >> >> >> >> >> >> >> MOV_CH_LAYOUT_USE_DESCRIPTIONS = ( 0 << 16) |
>> >> >> >> >> >> >> >> 0,
>> >> >> >> >> >> >> >> MOV_CH_LAYOUT_USE_BITMAP = ( 1 << 16) |
>> >> >> >> >> >> >> >> 0,
>> >> >> >> >> >> >> >> MOV_CH_LAYOUT_DISCRETEINORDER = (147 << 16) |
>> >> >> >> >> >> >> >> 0,
>> >> >> >> >> >> >> >> --
>> >> >> >> >> >> >> >> 2.6.2
>> >> >> >> >> >> >> >
>> >> >> >> >> >> >> >
>> >> >> >> >> >> >> > I personally don't really like these... I think both
>> >> >> >> >> >> >> > obfuscate
>> >> >> >> >> >> >> > the
>> >> >> >> >> >> >> > meaning
>> >> >> >> >> >> >> > of the flag values, particularly the first one.
>> >> >> >> >> >> >>
>> >> >> >> >> >> >> There is no real solution (recall apedec and the INT32_MIN
>> >> >> >> >> >> >> final
>> >> >> >> >> >> >> solution), barring adding a comment signifying our intent
>> >> >> >> >> >> >> (ie
>> >> >> >> >> >> >> the
>> >> >> >> >> >> >> desired hex mask). I can do this if you think it helps.
>> >> >> >> >> >> >
>> >> >> >> >> >> >
>> >> >> >> >> >> > The solution is to not care about ISO C if it doesn't fix
>> >> >> >> >> >> > real
>> >> >> >> >> >> > issues.
>> >> >> >> >> >> > :)
>> >> >> >> >> >>
>> >> >> >> >> >> This is where we will just have to agree to disagree, I
>> >> >> >> >> >> consider
>> >> >> >> >> >> this
>> >> >> >> >> >> issue "real enough" - it is a violation of the standard, and
>> >> >> >> >> >> POSIX
>> >> >> >> >> >> says nothing contrariwise unlike the function pointer/data
>> >> >> >> >> >> pointer
>> >> >> >> >> >> thing.
>> >> >> >> >> >
>> >> >> >> >> >
>> >> >> >> >> > Well, that doesn't really help figuring out a way to do this in
>> >> >> >> >> > a
>> >> >> >> >> > way
>> >> >> >> >> > that
>> >> >> >> >> > we all find acceptable. So let's do that instead.
>> >> >> >> >> >
>> >> >> >> >> > For the enum movChannelLayoutTag, I don't think we ever rely on
>> >> >> >> >> > it
>> >> >> >> >> > being
>> >> >> >> >> > an
>> >> >> >> >> > enum do we? In fact, I'd say that the solution you used for the
>> >> >> >> >> > DCA
>> >> >> >> >> > enums
>> >> >> >> >> > (use macros instead of enums) would work here also.
>> >> >> >> >>
>> >> >> >> >> Well, there are some arrays defined in terms of this. The type of
>> >> >> >> >> the
>> >> >> >> >> array will need to be changed appropriately. I hence gave this as
>> >> >> >> >> the
>> >> >> >> >> solution producing the minimal diff while sticking to the
>> >> >> >> >> standard.
>> >> >> >> >> This one I thus strongly prefer keeping it as in the above patch.
>> >> >> >> >
>> >> >> >> >
>> >> >> >> > Right, but it doesn't fix the issue. The individual bits of the
>> >> >> >> > value
>> >> >> >> > may
>> >> >> >> > have the same value as currently and you're not causing that one
>> >> >> >> > compiler
>> >> >> >> > warning. But you're still assigning a negative/signed value to a
>> >> >> >> > field
>> >> >> >> > that
>> >> >> >> > is used as unsigned. See this piece of code:
>> >> >> >> >
>> >> >> >> > struct MovChannelLayoutMap {
>> >> >> >> > uint32_t tag; << unsigned
>> >> >> >> > uint64_t layout;
>> >> >> >> > };
>> >> >> >> >
>> >> >> >> > static const struct MovChannelLayoutMap mov_ch_layout_map_misc[] =
>> >> >> >> > {
>> >> >> >> > [..]
>> >> >> >> > { MOV_CH_LAYOUT_UNKNOWN, 0 }, << assigning a
>> >> >> >> > signed/negative
>> >> >> >> > value
>> >> >> >>
>> >> >> >> So what? This is completely portable, signed to unsigned conversion
>> >> >> >> has well defined semantics (e.g
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >> https://stackoverflow.com/questions/50605/signed-to-unsigned-conversion-in-c-is-it-always-safe),
>> >> >> >> essentially guaranteeing identical bit patterns.
>> >> >> >
>> >> >> >
>> >> >> > Then why "fix" the enum?
>> >> >>
>> >> >> Because the hex literal to int conversion is implementation defined,
>> >> >> with no guarantees from the standard. It can in fact raise an
>> >> >> implementation defined signal.
>> >> >> The new method at least guarantees identical bit representation on 2's
>> >> >> complement (only thing we care/assume), and has well defined, i.e
>> >> >> specified semantics as given in the above link.
>> >> >
>> >> >
>> >> > This is getting very fuzzy very quickly. My impression is that you care
>> >> > more
>> >> > about one spec violation than the other because one raises a compiler
>> >> > warning but the other doesn't...
>> >>
>> >> No, I don't. That is simply false, read the point above. I care about
>> >> well defined semantics vs implementation defined behavior. I can't do
>> >> anything about "your impressions", over which I don't have much
>> >> influence.
>> >>
>> >> >
>> >> > But as said before, I like to be solution driven. Why not make enum
>> >> > MovChannelLayout a series of defines? Doesn't that solve all issues
>> >> > without
>> >> > the drawbacks?
>> >>
>> >> I am also "solution driven" - the fact that my solution does not match
>> >> yours does not mean in any way that I am less "solution driven".
>> >
>> >
>> > Wait, there's a misunderstanding here. I agree that your solution fixes the
>> > problem you're seeing. But, I raised an objection, so, we have a new
>> > problem. With "solution driven", I'm trying to help overcome my own
>> > objection and come up with a new, alternate solution that overcomes my
>> > objection, while still solving your problem. There may be other ways to do
>> > the same thing, and you're free to propose alternatives. But, like mine,
>> > they need to both fix your problem as well as overcome my objection.
>>
>> I proposed a comment as a solution to meet your readability concern.
>>
>> >
>> >> There is the concrete drawback of a larger diff and type change from
>> >> the enum array, etc and likely greater scope for mistakes as a result.
>> >
>> >
>> > Small vs. big diff is a "preference" in FFmpeg, that is, we "prefer" smaller
>> > diffs over bigger diffs, everything all being equal. However, not everything
>> > else is equal in this case. Plus, the diff is not that big.
>>
>> I still feel the benefits of the one line diff (with associated
>> comment) far outweigh the costs of your solution. Michael also raised
>> the related "prettiness" concern, and I feel your solution scores
>> negatively on that aspect compared to mine. Of course, that is
>> subjective.
>> In fact, while I by no means feel that my solution is close to
>> optimal, I feel strongly enough about your proposed solution to oppose
>> it with whatever means I have available, unless amended of course.
>>
>> I doubt this opposition amounts to much though, given your senior
>> state and my recent joining. Bugs get introduced for all kinds of
>> reasons, even in one liners and review. It is a simple fact that
>> larger diffs are likely more trouble, especially for something as
>> minor as this.
>
> maybe something like this could be a compromise ?
>
> --- a/libavformat/cinedec.c
> +++ b/libavformat/cinedec.c
> @@ -50,7 +50,7 @@ enum {
> CFA_BAYER = 3, /**< GB/RG */
> CFA_BAYERFLIP = 4, /**< RG/GB */
>
> - CFA_TLGRAY = 0x80000000,
> +#define CFA_TLGRAY 0x80000000
> CFA_TRGRAY = 0x40000000,
> CFA_BLGRAY = 0x20000000,
> CFA_BRGRAY = 0x10000000
> --- a/libavformat/mov_chan.c
> +++ b/libavformat/mov_chan.c
> @@ -45,7 +45,7 @@
> * do not specify a particular ordering of those channels."
> */
> enum MovChannelLayoutTag {
> - MOV_CH_LAYOUT_UNKNOWN = 0xFFFF0000,
> +#define MOV_CH_LAYOUT_UNKNOWN 0xFFFF0000
> MOV_CH_LAYOUT_USE_DESCRIPTIONS = ( 0 << 16) | 0,
> MOV_CH_LAYOUT_USE_BITMAP = ( 1 << 16) | 0,
> MOV_CH_LAYOUT_DISCRETEINORDER = (147 << 16) | 0,
>
Thanks a lot for your effort. I am happy with your solution for
mov_chan. For cinedec, I am anyway going to change and make all
CFA_*RAY flags based on a macro.
As long as Ronald (and others) are on board, I will rework and post patchv3.
> [...]
>
> --
> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Those who are too smart to engage in politics are punished by being
> governed by those who are dumber. -- Plato
>
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