From: mkver via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: ffmpeg-devel@ffmpeg.org
Cc: mkver <code@ffmpeg.org>
Subject: [FFmpeg-devel] [PATCH] avcodec/x86/mpegvideoencdsp_init: Fix left shift of negative number (PR #20733)
Date: Tue, 21 Oct 2025 10:14:32 -0000
Message-ID: <176104167373.25.10604662575085708468@7d278768979e> (raw)
PR #20733 opened by mkver
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20733
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20733.patch
Uncovered by UBSan when running the mpegvideoencdsp checkasm
test.
Will apply this tonight unless there are objections.
>From 05b8608c76e76b7d8b4ce5e86e0940244fbb737e Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Tue, 21 Oct 2025 12:11:55 +0200
Subject: [PATCH] avcodec/x86/mpegvideoencdsp_init: Fix left shift of negative
number
Uncovered by UBSan when running the mpegvideoencdsp checkasm
test.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
libavcodec/x86/mpegvideoencdsp_init.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libavcodec/x86/mpegvideoencdsp_init.c b/libavcodec/x86/mpegvideoencdsp_init.c
index 3cd16fefbf..bf5b722016 100644
--- a/libavcodec/x86/mpegvideoencdsp_init.c
+++ b/libavcodec/x86/mpegvideoencdsp_init.c
@@ -42,7 +42,7 @@ static int try_8x8basis_ssse3(const int16_t rem[64], const int16_t weight[64], c
x86_reg i=0;
av_assert2(FFABS(scale) < MAX_ABS);
- scale <<= 16 + SCALE_OFFSET - BASIS_SHIFT + RECON_SHIFT;
+ scale *= 1 << (16 + SCALE_OFFSET - BASIS_SHIFT + RECON_SHIFT);
__asm__ volatile(
"pxor %%xmm2, %%xmm2 \n\t"
@@ -87,7 +87,7 @@ static void add_8x8basis_ssse3(int16_t rem[64], const int16_t basis[64], int sca
x86_reg i=0;
if (FFABS(scale) < 1024) {
- scale <<= 16 + SCALE_OFFSET - BASIS_SHIFT + RECON_SHIFT;
+ scale *= 1 << (16 + SCALE_OFFSET - BASIS_SHIFT + RECON_SHIFT);
__asm__ volatile(
"movd %3, %%xmm2 \n\t"
"punpcklwd %%xmm2, %%xmm2 \n\t"
--
2.49.1
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