[FFmpeg-devel] [PATCH 1/2] avcodec/vda_h264: use multichar literal portably

[Ganesh Ajjanagadde]

On Sat, Sep 19, 2015 at 2:27 AM, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> On Sat, Sep 19, 2015 at 12:35 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
>> On Fri, Sep 18, 2015 at 06:16:18PM -0400, Ganesh Ajjanagadde wrote:
>>> Multichar literals are implementation defined, and thus trigger -Wmultichar:
>>> http://fate.ffmpeg.org/log.cgi?time=20150918202532&log=compile&slot=x86_64-darwin-gcc-5.
>>> http://www.zipcon.net/~swhite/docs/computers/languages/c_multi-char_const.html
>>> gives a good summary of how to deal with them; in particular this patch
>>> results in behavior identical to that generated by GCC (which I assume is correct this case).
>>>
>>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>>> ---
>>>  libavcodec/vda_h264.c | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/libavcodec/vda_h264.c b/libavcodec/vda_h264.c
>>> index 8c526c0..3279afa 100644
>>> --- a/libavcodec/vda_h264.c
>>> +++ b/libavcodec/vda_h264.c
>>> @@ -339,7 +339,9 @@ int ff_vda_default_init(AVCodecContext *avctx)
>>>      CFMutableDictionaryRef buffer_attributes;
>>>      CFMutableDictionaryRef io_surface_properties;
>>>      CFNumberRef cv_pix_fmt;
>>> -    int32_t fmt = 'avc1', pix_fmt = vda_ctx->cv_pix_fmt_type;
>>> +#define LE_CHR(a,b,c,d) ( ((a)<<24) | ((b)<<16) | ((c)<<8) | (d) )
>>> +    int32_t fmt = LE_CHR( 'a', 'v', 'c', '1');
>>
>> please use AV_RB32("avc1")
>> its simpler and used elsewhere
>>
>
> IMHO even better is MKBETAG( 'a', 'v', 'c', '1')

I do not know about the technical merits of this, but there is
certainly one drawback of MKBETAG as compared to AV_RB32: MKBETAG
can't be grepped as easily for (one can't just grep avc1).

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