[FFmpeg-devel] Multimedia extensions run-time support check
Wed Jun 25 03:46:01 CEST 2008
On Tue, Jun 24, 2008 at 07:24:52PM -0400, Alexander Strange wrote:
> On Jun 24, 2008, at 4:23 PM, Michael Niedermayer wrote:
>> On Tue, Jun 24, 2008 at 05:43:49PM +0200, Laurent Desnogues wrote:
>>> (I know this is not a very interesting matter, but it's a good way
>>> for me to start messing with FFmpeg code; if noone cares, let
>>> me know and I'll use some adhoc solution that fits my needs.)
>>> Currently to know what multimedia extensions are supported,
>>> the code checks the value of mm_flags or the return value of
>>> mm_support() (cf. dsputil.h).
>>> My understanding is that this is only used to setup things at
>>> initialization time.
>>> However I find things are inconsistent. For instance:
>>> - mm_support is always declared but only defined for MMX,
>>> IWMMXT (Xscale) and PPC
>>> - mm_flags is declared for ARMV4L but only defined for
>>> This is not a big deal at the moment since it only breaks
>>> the build of some test programs for some configs, such as
>>> dct-test when either MMX is not defined or when building
>>> for ARM without IWMMXT.
>> dct-test.c was broken by
>> Author: benoit
>> Date: Tue Mar 25 15:34:27 2008
>> New Revision: 12580
>> Set mm_flags in dct-test to fix floating math.
>> Patch by Alexander Strange \astrange ithinksw com/
>> Author: gpoirier
>> Date: Sun Mar 30 12:29:28 2008
>> New Revision: 12628
>> check mm_flags for each DCT and skips the ones that can't be run
>> patch by Alexander Strange %astrange A ithinksw P com%
>> fft-test.c was broken by
>> Author: diego
>> Date: Tue Jun 24 11:00:58 2008
>> New Revision: 13940
>> Remove redundant mm_flags declaration, fixes the warning:
>> libavcodec.a(dsputil_ppc.o): warning: definition of `mm_flags'
>> overriding common
>> fft-test.o: warning: common is here
>>> Currently I only see two solutions:
>>> 1. correctly protect declarations in dsputil.h depending
>>> on ifdef's
>>> 2. always define fake mm_flags and mm_support that
>>> are or return zero.
>> I do not belive mm_flags was ever intended to be accessed from outside
>> the specific optimized code. it just happened by mistake as people tried
>> to "fix" gcc warnings without bothering to fully understand the code
>> mm_support() should be a #define 0 when optims are off.
> Is this OK?
no, just use a variable that does not conflict with mm_flags. like a local
var or a different name.
Besides i do not think fft-test.c should be linked with dsputil*
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Size: 189 bytes
Desc: Digital signature
More information about the ffmpeg-devel