[FFmpeg-devel] [PATCH] Use clear_blocks instead of memset in vp3.c

Michael Niedermayer michaelni
Sun Aug 31 01:44:56 CEST 2008

On Sat, Aug 30, 2008 at 03:00:00PM -0700, Baptiste Coudurier wrote:
> Hi,
> David Conrad wrote:
> > On Aug 30, 2008, at 3:05 PM, David Conrad wrote:
> > 
> >> Hi,
> >>
> >> This uses the dsp clear_blocks() function to zero blocks in vp3  
> >> rather than memset.
> > 
> > Sorry, ignore this, I didn't realize clear_blocks was plural (yes I  
> > should test patches before sending them...)
> However, a version of clear_blocks that would take number of blocks to
> clear is welcome, I know several places where it would be useful.

yes though it may not be as usefull as it seems
clearing 64 16bit words with mmx needs just
16 instructions, 
the loop will add about 3
then there is call overhead, returning pushing parameters on the stack
getting them off the stack againm the dsp pointer and soon clearing a
single block will spend most of its time in things completely unrelated to the
actual clearing.
Now if this is compared to plain C clearing with int32 or int64 writes
but inlined or memset that is generated by a sane compiler, the clear_1block
code may suddenly not be that much better anymore ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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