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new a1a7737c4b avcodec/dvbsubdec: compute the clut scores incrementally
a1a7737c4b is described below
commit a1a7737c4bcace8615f70b8f2cc7fc515ca26522
Author: romainhedouin <[email protected]>
AuthorDate: Mon Nov 2 01:15:39 2026 +0100
Commit: kierank <[email protected]>
CommitDate: Mon Nov 2 23:38:02 2026 +0000
avcodec/dvbsubdec: compute the clut scores incrementally
compute_default_clut() recomputed the score of every candidate from
scratch, summing over all 256 colours, each time a colour was added to
the list: up to 256 * 256 * 256 multiply-adds per region. Keep the
scores and add the contribution of the new colour instead. The output
is unchanged.
Noticed during a review sweep of ffmpeg using an LLM.
Signed-off-by: romainhedouin <[email protected]>
---
libavcodec/dvbsubdec.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/libavcodec/dvbsubdec.c b/libavcodec/dvbsubdec.c
index 0256e8355d..2426da896d 100644
--- a/libavcodec/dvbsubdec.c
+++ b/libavcodec/dvbsubdec.c
@@ -673,6 +673,7 @@ static void compute_default_clut(DVBSubContext *ctx,
uint8_t *clut, AVSubtitleRe
uint8_t list[256] = {0};
uint8_t list_inv[256];
int counttab[256] = {0};
+ int scoretab[256];
int (*counttab2)[256] = ctx->clut_count2;
int count, i, x, y;
ptrdiff_t stride = rect->linesize[0];
@@ -699,18 +700,15 @@ static void compute_default_clut(DVBSubContext *ctx,
uint8_t *clut, AVSubtitleRe
for (i = 0; i<256; i++) {
counttab2[i+1][i] = 0;
}
+ memcpy(scoretab, counttab2[0], sizeof(scoretab));
for (i = 0; i<256; i++) {
int bestscore = 0;
int bestv = 0;
for (x = 0; x < 256; x++) {
- int scorev = 0;
+ int scorev = scoretab[x];
if (list[x])
continue;
- scorev += counttab2[0][x];
- for (y = 0; y < 256; y++) {
- scorev += list[y] * counttab2[y+1][x];
- }
if (scorev) {
int score = 1024LL*scorev / counttab[x];
@@ -724,6 +722,8 @@ static void compute_default_clut(DVBSubContext *ctx,
uint8_t *clut, AVSubtitleRe
break;
list [ bestv ] = 1;
list_inv[ i ] = bestv;
+ for (x = 0; x < 256; x++)
+ scoretab[x] += counttab2[bestv+1][x];
}
count = FFMAX(i - 1, 1);
--
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