On Fri, Jun 22, 2012 at 09:42:36PM +0100, Mans Rullgard wrote:
> The problem is that the ssse3 psign instruction does the wrong
> thing here. Commit ea60dfe incorrectly removed a macro emulating
> this instruction for pre-ssse3 code. However, the emulation is
> incorrect, and the code relies on the behaviour of the macro.
> Specifically, the psign sets destination elements to zero where
> the corresponding source element is zere, whereas the emulation
^^^ bad accent
> only negates destination elements where the source is zero.
>
> Furthermore, the PSIGNW_MMX macro in x86util.asm is totally bogus,
> which is why the original VC1 code had an additional right shift
VC-1
> when using it. Since the psign instruction cannot be used here,
> skip all the macro hell and use the working instruction sequence
> directly.
>
> None of this was noticed due a stray return statement in
> ff_vc1dsp_init_mmx() which meant that only the mmx version of the
> loop filter was ever used (before being removed in ea60dfe).
>
> Signed-off-by: Mans Rullgard <[email protected]>
> ---
> libavcodec/x86/vc1dsp_mmx.c | 2 +-
> libavcodec/x86/vc1dsp_yasm.asm | 5 +++--
> 2 files changed, 4 insertions(+), 3 deletions(-)
The patch itself LGTM
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