* [FFmpeg-devel] [PATCH] lavc/aarch64: Fix addp overflow in ff_pred16x16_plane_neon_10 (PR #20744)
@ 2025-10-24 8:33 pengbin via ffmpeg-devel
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From: pengbin via ffmpeg-devel @ 2025-10-24 8:33 UTC (permalink / raw)
To: ffmpeg-devel; +Cc: pengbin
PR #20744 opened by pengbin
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20744
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20744.patch
The mismatch between neon and C functions can be reproduced
using the following bitstream and command line on aarch64 devices.
wget https://streams.videolan.org/ffmpeg/incoming/replay_intra_pred_16x16.h264
./ffmpeg -cpuflags 0 -threads 1 -i replay_intra_pred_16x16.h264 -f framemd5 -y md5_ref
./ffmpeg -threads 1 -i replay_intra_pred_16x16.h264 -f framemd5 -y md5_neon
Signed-off-by: Bin Peng <pengbin@visionular.com>
>From 10a5e0c71ca498b978c216d141750257541d60e0 Mon Sep 17 00:00:00 2001
From: Bin Peng <pengbin@visionular.com>
Date: Fri, 24 Oct 2025 15:58:08 +0800
Subject: [PATCH] lavc/aarch64: Fix addp overflow in ff_pred16x16_plane_neon_10
The mismatch between neon and C functions can be reproduced
using the following bitstream and command line on aarch64 devices.
wget https://streams.videolan.org/ffmpeg/incoming/replay_intra_pred_16x16.h264
./ffmpeg -cpuflags 0 -threads 1 -i replay_intra_pred_16x16.h264 -f framemd5 -y md5_ref
./ffmpeg -threads 1 -i replay_intra_pred_16x16.h264 -f framemd5 -y md5_neon
Signed-off-by: Bin Peng <pengbin@visionular.com>
---
libavcodec/aarch64/h264pred_neon.S | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/libavcodec/aarch64/h264pred_neon.S b/libavcodec/aarch64/h264pred_neon.S
index d0999938ef..795d2ce540 100644
--- a/libavcodec/aarch64/h264pred_neon.S
+++ b/libavcodec/aarch64/h264pred_neon.S
@@ -489,10 +489,10 @@ function ff_pred16x16_plane_neon_10, export=1
mul v2.8h, v2.8h, v0.8h
mul v3.8h, v3.8h, v0.8h
addp v2.8h, v2.8h, v3.8h
- addp v2.8h, v2.8h, v2.8h
- addp v2.4h, v2.4h, v2.4h
- sshll v3.4s, v2.4h, #2
- saddw v2.4s, v3.4s, v2.4h
+ saddlp v2.4s, v2.8h
+ addp v2.4s, v2.4s, v2.4s
+ shl v3.4s, v2.4s, #2
+ add v2.4s, v3.4s, v2.4s
rshrn v4.4h, v2.4s, #6
trn2 v5.4h, v4.4h, v4.4h
add v2.4h, v4.4h, v5.4h
@@ -506,14 +506,13 @@ function ff_pred16x16_plane_neon_10, export=1
sxtl v6.4s, v5.4h // c
mov v0.h[0], wzr
- mul v0.8h, v0.8h, v4.h[0]
dup v16.4s, v2.s[0]
dup v17.4s, v2.s[0]
dup v2.8h, v4.h[0] // b
dup v3.4s, v6.s[0] // c
sshll v2.4s, v2.4h, #3 // b * 8
- saddw v16.4s, v16.4s, v0.4h
- saddw2 v17.4s, v17.4s, v0.8h
+ smlal v16.4s, v0.4h, v4.h[0]
+ smlal2 v17.4s, v0.8h, v4.h[0]
sub v3.4s, v3.4s, v2.4s
mov w3, #16
--
2.49.1
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2025-10-24 8:33 [FFmpeg-devel] [PATCH] lavc/aarch64: Fix addp overflow in ff_pred16x16_plane_neon_10 (PR #20744) pengbin via ffmpeg-devel
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