Re: [FFmpeg-devel] [PATCH 02/15] avfilter/vf_bwdif: Add common macros and consts for aarch64 neon

["Martin Storsjö" <martin@martin.st>]

On Sun, 2 Jul 2023, John Cox wrote:

> On Sun, 2 Jul 2023 00:35:14 +0300 (EEST), you wrote:
>
>> On Thu, 29 Jun 2023, John Cox wrote:
>>
>>> Add macros for dual scalar half->single multiply and accumulate
>>> Add macro for shift, saturate and shorten single to byte
>>> Add filter constants
>>>
>>> Signed-off-by: John Cox <jc@kynesim.co.uk>
>>> ---
>>> libavfilter/aarch64/vf_bwdif_neon.S | 46 +++++++++++++++++++++++++++++
>>> 1 file changed, 46 insertions(+)
>>>
>>> diff --git a/libavfilter/aarch64/vf_bwdif_neon.S b/libavfilter/aarch64/vf_bwdif_neon.S
>>> index 639ab22998..a8f0ed525a 100644
>>> --- a/libavfilter/aarch64/vf_bwdif_neon.S
>>> +++ b/libavfilter/aarch64/vf_bwdif_neon.S
>>> @@ -23,3 +23,49 @@
>>>
>>> #include "libavutil/aarch64/asm.S"
>>>
>>> +.macro SQSHRUNN b, s0, s1, s2, s3, n
>>> +        sqshrun         \s0\().4h, \s0\().4s, #\n - 8
>>> +        sqshrun2        \s0\().8h, \s1\().4s, #\n - 8
>>> +        sqshrun         \s1\().4h, \s2\().4s, #\n - 8
>>> +        sqshrun2        \s1\().8h, \s3\().4s, #\n - 8
>>> +        uzp2            \b\().16b, \s0\().16b, \s1\().16b
>>> +.endm
>>> +
>>> +.macro SMULL4K a0, a1, a2, a3, s0, s1, k
>>> +        smull           \a0\().4s, \s0\().4h, \k
>>> +        smull2          \a1\().4s, \s0\().8h, \k
>>> +        smull           \a2\().4s, \s1\().4h, \k
>>> +        smull2          \a3\().4s, \s1\().8h, \k
>>> +.endm
>>> +
>>> +.macro UMULL4K a0, a1, a2, a3, s0, s1, k
>>> +        umull           \a0\().4s, \s0\().4h, \k
>>> +        umull2          \a1\().4s, \s0\().8h, \k
>>> +        umull           \a2\().4s, \s1\().4h, \k
>>> +        umull2          \a3\().4s, \s1\().8h, \k
>>> +.endm
>>> +
>>> +.macro UMLAL4K a0, a1, a2, a3, s0, s1, k
>>> +        umlal           \a0\().4s, \s0\().4h, \k
>>> +        umlal2          \a1\().4s, \s0\().8h, \k
>>> +        umlal           \a2\().4s, \s1\().4h, \k
>>> +        umlal2          \a3\().4s, \s1\().8h, \k
>>> +.endm
>>> +
>>> +.macro UMLSL4K a0, a1, a2, a3, s0, s1, k
>>> +        umlsl           \a0\().4s, \s0\().4h, \k
>>> +        umlsl2          \a1\().4s, \s0\().8h, \k
>>> +        umlsl           \a2\().4s, \s1\().4h, \k
>>> +        umlsl2          \a3\().4s, \s1\().8h, \k
>>> +.endm
>>> +
>>> +// static const uint16_t coef_lf[2] = { 4309, 213 };
>>> +// static const uint16_t coef_hf[3] = { 5570, 3801, 1016 };
>>> +// static const uint16_t coef_sp[2] = { 5077, 981 };
>>> +
>>> +        .align 16
>>
>> Note that .align for arm is power of two; this triggers a 2^16 byte
>> alignment here, which certainly isn't intended.
>
> Yikes! I'll swap that for a .balign now I've looked that up
>
>> But in general, the usual way of defining constants is with a
>> const/endconst block, which places them in the right rdata section instead
>> of in the text section. But that then requires you to use a movrel macro
>> for accessing the data, instead of a plain ldr instruction.
>
> Yeah - arm has a history of mixing text & const - I went with the
> simpler code. Is this a deal breaker or can I leave it as is?

I wouldn't treat it as a deal breaker as long as it works across all 
platforms - even if consistency with the code style elsewhere is 
preferred, but IIRC there may be issues with MS armasm (after passed 
through gas-preprocessor). IIRC there might be issues with starting out 
with straight up content without the full setup made by the function/const 
macros. OTOH I might have fixed that in gas-preprocessor too...

Last time around, the patchset failed building in that configuration due 
ot the out of range alignment, I'll see how it fares now.

// Martin

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