[FFmpeg-devel] [PR] avcodec/prores_raw: use av_popcount instead of limited lookup table (PR #21505)

[FFmpeg-devel] [PR] avcodec/prores_raw: use av_popcount instead of limited lookup table (PR #21505)

[Timo Rothenpieler via ffmpeg-devel]

PR #21505 opened by Timo Rothenpieler (BtbN)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21505
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21505.patch

The calculation can yield bigger values than the lookup table provides.
So just use actual popcount instead.

Fixes #21503


>From 7379539685ec900b372d87ad25a23e82b8b45f17 Mon Sep 17 00:00:00 2001
From: Timo Rothenpieler <timo@rothenpieler.org>
Date: Sun, 18 Jan 2026 18:52:52 +0100
Subject: [PATCH] avcodec/prores_raw: use av_popcount instead of limited lookup
 table

The calculation can yield bigger values than the lookup table provides.
So just use actual popcount instead.

Fixes #21503
---
 libavcodec/prores_raw.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/libavcodec/prores_raw.c b/libavcodec/prores_raw.c
index 8be566ed36..eb1a9af14f 100644
--- a/libavcodec/prores_raw.c
+++ b/libavcodec/prores_raw.c
@@ -93,10 +93,6 @@ static uint16_t get_value(GetBitContext *gb, int16_t codebook)
 
 #define TODCCODEBOOK(x) ((x + 1) >> 1)
 
-static const uint8_t align_tile_w[16] = {
-    0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
-};
-
 #define DC_CB_MAX 12
 const uint8_t ff_prores_raw_dc_cb[DC_CB_MAX + 1] = {
     0x010, 0x021, 0x032, 0x033, 0x033, 0x033, 0x044, 0x044, 0x044, 0x044, 0x044, 0x044, 0x076,
@@ -432,7 +428,7 @@ static int decode_frame(AVCodecContext *avctx,
 
     s->nb_tw = (w + 15) >> 4;
     s->nb_th = (h + 15) >> 4;
-    s->nb_tw = (s->nb_tw >> align) + align_tile_w[~(-1 * (1 << align)) & s->nb_tw];
+    s->nb_tw = (s->nb_tw >> align) + av_popcount(~(-1 * (1 << align)) & s->nb_tw);
     s->nb_tiles = s->nb_tw * s->nb_th;
     av_log(avctx, AV_LOG_DEBUG, "%dx%d | nb_tiles: %d\n", s->nb_tw, s->nb_th, s->nb_tiles);
 
-- 
2.52.0

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