Hi, On Sun, Jul 15, 2012 at 3:31 PM, Måns Rullgård <[email protected]> wrote: > "Ronald S. Bultje" <[email protected]> writes: > >> Hi, >> >> On Sun, Jul 8, 2012 at 1:34 PM, Luca Barbato <[email protected]> wrote: >>> On 07/06/2012 07:55 PM, Ronald S. Bultje wrote: >>>> From: "Ronald S. Bultje" <[email protected]> >>>> >>>> MSVC has incomplete variadic macro argument handling, meaning it does >>>> support it to some extend, but it will basically handle all variadic >>>> arguments as a single argument, including the comma that separates them, >>>> thus making it useless for anything else than as a function argument. >>>> Our implementation of LOCAL_ALIGNED() breaks because of this, thus here >>>> we implement an alternative form of LOCAL_ALIGNED() that does not use >>>> variadic macro arguments. >>>> --- >>>> configure | 1 + >>>> libavcodec/aacps.c | 10 +++++----- >>>> libavcodec/aacsbr.c | 2 +- >>>> libavcodec/ac3enc.c | 2 +- >>>> libavcodec/ac3enc_template.c | 4 ++-- >>>> libavcodec/dsputil.h | 26 ++++++++++++++++++-------- >>>> libavcodec/dvdec.c | 2 +- >>>> libavcodec/h264_loopfilter.c | 2 +- >>>> libavcodec/ra288.c | 6 +++--- >>>> 9 files changed, 33 insertions(+), 22 deletions(-) >>> >>> As reported in the bug closed as WontFix[1], a second expansion solves >>> the problem, I tested in my personal msvc tree and it seems working. >>> >>> Probably it could be implemented with a sed replacement as well so it >>> won't hinder normal development. >>> >>> lu >>> >>> [1] >>> http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement >> >> That still requires source code modifications, which seems to hit a >> brick wall here. >> >> I've looked at http://msdn.microsoft.com/en-us/library/ms177415(v=vs.80).aspx >> and http://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html, and it's >> clear that something like #define LOCAL_ALIGNED_16(t, v, s, ...) has >> theoretical issues if defined to a function (#define eprintf(format, >> ...) fprintf(stderr, format, __VA_ARGS__) with eprintf("hi\n") becomes >> fprintf(stderr, "hi\n", ), i.e. an empty terminal comma). However, >> both appear to support this form when used on variadic macros (and in >> fact also when used on a vararg functions like fprintf). So I could do >> something like: > > Of course this doesn't work. The standard requires that every > invocation of a variadic macro supply at least one argument for the > variable argument list. Your example does not do this. Some compilers > will not even compile it. > >> #define LOCAL_ALIGNED_16(t, v, s, ...) LOCAL_ALIGNED_D(16, t, v, s, >> __VA_ARGS__,) >> >> instead of >> >> #define LOCAL_ALIGNED_16(t, v, ...) LOCAL_ALIGNED_D(16, t, v, __VA_ARGS__,,) >> >> and to the best of my knowledge, since the called macro itself is >> always variadic also, this should actually work - not just on these >> two compilers, but on any compiler. Is there a specific reason we >> don't use this instead? > > Yes, the code is the way it is because that is how the standard requires > it. Your suggestion will break with some strictly conforming compilers.
I mentioned this very fact in my email. However, your quote is only true for functions, not macros. Here, the variadic macro calls a macro, not a function, so your claim is incorrect. A macro with an empty argument is perfectly valid; in fact, the current code relies on two empty arguments. Instead of saying "rejected", which you undoubtedly will do, can you please think constructively on how we can fix this? Ronald _______________________________________________ libav-devel mailing list [email protected] https://lists.libav.org/mailman/listinfo/libav-devel
