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avcodec/smacker: Remove redundant checks when reading VLC codes 

The VLC codes in question originate from a Huffmann tree and so every
sequence of bits that is longer than the longest code contains an
initial sequence that is a valid code. Given that it has been checked
during reading said tree (and once again in ff_init_vlc_sparse()) that
the length of each code is <= 3 * the number of bits read at once when
reading codes, get_vlc2() will always find a matching entry.

These checks have been added in 71d3c25a7e
at a time when the length of the codes had not been checked when parsing
the tree.

For GCC 9 and the sample from ticket #2425 this led to a slight
performance regression: The time for one call to smka_decode_frame()
increased from 2053671 to 2064529 decicycles; for Clang 9, performance
improved from 1521288 to 1508459 decicycles.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2020-07-25 15:14:53 +02:00
parent 943a458157
commit 3899adc298
1 changed files with 0 additions and 32 deletions
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32
libavcodec/smacker.c
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@ -140,8 +140,6 @@ static int smacker_decode_bigtree(GetBitContext *gb, HuffContext *hc,
int val, i1, i2;
i1 = ctx->v1->table ? get_vlc2(gb, ctx->v1->table, SMKTREE_BITS, 3) : 0;
i2 = ctx->v2->table ? get_vlc2(gb, ctx->v2->table, SMKTREE_BITS, 3) : 0;
if (i1 < 0 || i2 < 0)
return AVERROR_INVALIDDATA;
val = ctx->recode1[i1] | (ctx->recode2[i2] << 8);
if(val == ctx->escapes[0]) {
ctx->last[0] = hc->current;
@ -678,21 +676,11 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
res = get_vlc2(&gb, vlc[2].table, SMKTREE_BITS, 3);
else
res = 0;
if (res < 0) {
av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
ret = AVERROR_INVALIDDATA;
goto error;
}
val = h[2].values[res];
if(vlc[3].table)
res = get_vlc2(&gb, vlc[3].table, SMKTREE_BITS, 3);
else
res = 0;
if (res < 0) {
av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
ret = AVERROR_INVALIDDATA;
goto error;
}
val |= h[3].values[res] << 8;
pred[1] += (unsigned)sign_extend(val, 16);
*samples++ = pred[1];
@ -701,21 +689,11 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
res = get_vlc2(&gb, vlc[0].table, SMKTREE_BITS, 3);
else
res = 0;
if (res < 0) {
av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
ret = AVERROR_INVALIDDATA;
goto error;
}
val = h[0].values[res];
if(vlc[1].table)
res = get_vlc2(&gb, vlc[1].table, SMKTREE_BITS, 3);
else
res = 0;
if (res < 0) {
av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
ret = AVERROR_INVALIDDATA;
goto error;
}
val |= h[1].values[res] << 8;
pred[0] += (unsigned)sign_extend(val, 16);
*samples++ = pred[0];
@ -736,11 +714,6 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
res = get_vlc2(&gb, vlc[1].table, SMKTREE_BITS, 3);
else
res = 0;
if (res < 0) {
av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
ret = AVERROR_INVALIDDATA;
goto error;
}
pred[1] += sign_extend(h[1].values[res], 8);
*samples8++ = pred[1];
} else {
@ -748,11 +721,6 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
res = get_vlc2(&gb, vlc[0].table, SMKTREE_BITS, 3);
else
res = 0;
if (res < 0) {
av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
ret = AVERROR_INVALIDDATA;
goto error;
}
pred[0] += sign_extend(h[0].values[res], 8);
*samples8++ = pred[0];
}