"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. -- Måns Rullgård [email protected] _______________________________________________ libav-devel mailing list [email protected] https://lists.libav.org/mailman/listinfo/libav-devel
