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

[Martin Storsjö]

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 <j...@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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