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Code Issues Releases Activity

avcodec/mjpegdec: Remove unnecessary reloads

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Hint: The parts of this patch in decode_block_progressive()
and decode_block_refinement() rely on the fact that GET_VLC
returns -1 on error, so that it enters the codepaths for
actually coded block coefficients.

Reviewed-by: Ramiro Polla <ramiro.polla@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt
2025-10-08 03:12:19 +02:00
parent dad06a445f
commit ce9d181444
1 changed files with 7 additions and 8 deletions
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15
libavcodec/mjpegdec.c
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@@ -854,9 +854,9 @@ static int decode_block(MJpegDecodeContext *s, int16_t *block, int component,
i += ((unsigned)code) >> 4;
code &= 0xf;
if (code) {
if (code > MIN_CACHE_BITS - 16)
UPDATE_CACHE(re, &s->gb);
// GET_VLC updates the cache if parsing reaches the second stage.
// So we have at least MIN_CACHE_BITS - 9 > 15 bits left here
// and don't need to refill the cache.
{
int cache = GET_CACHE(re, &s->gb);
int sign = (~cache) >> 31;
@@ -918,8 +918,6 @@ static int decode_block_progressive(MJpegDecodeContext *s, int16_t *block,
code &= 0xF;
if (code) {
i += run;
if (code > MIN_CACHE_BITS - 16)
UPDATE_CACHE(re, &s->gb);
{
int cache = GET_CACHE(re, &s->gb);
@@ -950,7 +948,8 @@ static int decode_block_progressive(MJpegDecodeContext *s, int16_t *block,
} else {
val = (1 << run);
if (run) {
UPDATE_CACHE(re, &s->gb);
// Given that GET_VLC reloads internally, we always
// have at least 16 bits in the cache here.
val += NEG_USR32(GET_CACHE(re, &s->gb), run);
LAST_SKIP_BITS(re, &s->gb, run);
}
@@ -1012,7 +1011,6 @@ static int decode_block_refinement(MJpegDecodeContext *s, int16_t *block,
if (code & 0xF) {
run = ((unsigned) code) >> 4;
UPDATE_CACHE(re, &s->gb);
val = SHOW_UBITS(re, &s->gb, 1);
LAST_SKIP_BITS(re, &s->gb, 1);
ZERO_RUN;
@@ -1033,7 +1031,8 @@ static int decode_block_refinement(MJpegDecodeContext *s, int16_t *block,
val = run;
run = (1 << run);
if (val) {
UPDATE_CACHE(re, &s->gb);
// Given that GET_VLC reloads internally, we always
// have at least 16 bits in the cache here.
run += SHOW_UBITS(re, &s->gb, val);
LAST_SKIP_BITS(re, &s->gb, val);
}