[FFmpeg-devel] [PATCHv2] all: fix enum definition for large values

[Ganesh Ajjanagadde]

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.

>
> Ronald