mirror of https://git.ffmpeg.org/ffmpeg.git
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:
parent
943a458157
commit
3899adc298
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@ -140,8 +140,6 @@ static int smacker_decode_bigtree(GetBitContext *gb, HuffContext *hc,
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int val, i1, i2;
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i1 = ctx->v1->table ? get_vlc2(gb, ctx->v1->table, SMKTREE_BITS, 3) : 0;
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i2 = ctx->v2->table ? get_vlc2(gb, ctx->v2->table, SMKTREE_BITS, 3) : 0;
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if (i1 < 0 || i2 < 0)
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return AVERROR_INVALIDDATA;
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val = ctx->recode1[i1] | (ctx->recode2[i2] << 8);
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if(val == ctx->escapes[0]) {
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ctx->last[0] = hc->current;
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@ -678,21 +676,11 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
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res = get_vlc2(&gb, vlc[2].table, SMKTREE_BITS, 3);
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else
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res = 0;
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if (res < 0) {
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av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
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ret = AVERROR_INVALIDDATA;
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goto error;
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}
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val = h[2].values[res];
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if(vlc[3].table)
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res = get_vlc2(&gb, vlc[3].table, SMKTREE_BITS, 3);
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else
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res = 0;
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if (res < 0) {
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av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
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ret = AVERROR_INVALIDDATA;
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goto error;
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}
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val |= h[3].values[res] << 8;
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pred[1] += (unsigned)sign_extend(val, 16);
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*samples++ = pred[1];
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@ -701,21 +689,11 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
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res = get_vlc2(&gb, vlc[0].table, SMKTREE_BITS, 3);
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else
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res = 0;
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if (res < 0) {
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av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
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ret = AVERROR_INVALIDDATA;
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goto error;
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}
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val = h[0].values[res];
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if(vlc[1].table)
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res = get_vlc2(&gb, vlc[1].table, SMKTREE_BITS, 3);
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else
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res = 0;
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if (res < 0) {
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av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
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ret = AVERROR_INVALIDDATA;
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goto error;
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}
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val |= h[1].values[res] << 8;
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pred[0] += (unsigned)sign_extend(val, 16);
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*samples++ = pred[0];
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@ -736,11 +714,6 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
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res = get_vlc2(&gb, vlc[1].table, SMKTREE_BITS, 3);
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else
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res = 0;
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if (res < 0) {
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av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
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ret = AVERROR_INVALIDDATA;
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goto error;
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}
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pred[1] += sign_extend(h[1].values[res], 8);
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*samples8++ = pred[1];
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} else {
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@ -748,11 +721,6 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
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res = get_vlc2(&gb, vlc[0].table, SMKTREE_BITS, 3);
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else
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res = 0;
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if (res < 0) {
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av_log(avctx, AV_LOG_ERROR, "invalid vlc\n");
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ret = AVERROR_INVALIDDATA;
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goto error;
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}
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pred[0] += sign_extend(h[0].values[res], 8);
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*samples8++ = pred[0];
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}
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