[xine-user] Compiler warning: "Operation may be undefined"...

[Chris R. <ran...@ya...>]

Hi,
I'm seeing this compiler warning in the latest CVS
xine-lib:

video_out_syncfb.c: In function
`write_frame_YUV420P2':
video_out_syncfb.c:199: warning: operation on `rcr'
may be undefined
video_out_syncfb.c:199: warning: operation on `rcb'
may be undefined
video_out_syncfb.c:200: warning: operation on `rcr'
may be undefined
video_out_syncfb.c:200: warning: operation on `rcb'
may be undefined


The code in question is two lines like this:

*tmp32++ = (*rcr++) | (*rcb++)<<8 | (*rcr++)<<16 |
(*rcb++)<<24;

I think that the compiler is saying that there is *no
guarantee* that these expressions involving 'rcr' and
'rcb' will be evaluated in any particular order. And
obviously, the order is rather important. My guess is
that the tester's compiler 'just happens' to get the
order right at the moment.

Maybe these lines could be uncondensed slightly to
make the code non-ambiguous?

Cheers,
Chris


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