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avcodec/smacker: Improve creating Huffman VLC tables

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The Smacker Huffman tables are already stored in a tree-like structure;
in particular, they are naturally ordered from left to right in the
tree and are therefore suitable to be initialized by
ff_init_vlc_from_lengths() which avoids traversing the data twice in
order to sort only the codes that are so long that they need into a
subtable.

This improves performance (and reduces codesize): For the sample from
ticket #2425 the number of decicycles for parsing and creating the VLCs
in smka_decode_frame() decreased from 412322 to 359152 (tested with
10 runs each looping 20 times over the file).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2020-10-25 10:24:31 +01:00
parent 09062eece2
commit fefe2cbbf2
1 changed files with 22 additions and 24 deletions
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46
libavcodec/smacker.c
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@ -62,14 +62,17 @@ typedef struct SmackVContext {
int mmap_last[3], mclr_last[3], full_last[3], type_last[3]; int mmap_last[3], mclr_last[3], full_last[3], type_last[3];
} SmackVContext; } SmackVContext;
typedef struct HuffEntry {
uint8_t value;
uint8_t length;
} HuffEntry;
/** /**
* Context used for code reconstructing * Context used for code reconstructing
*/ */
typedef struct HuffContext { typedef struct HuffContext {
int current; int current;
uint32_t bits[256]; HuffEntry entries[256];
uint8_t lengths[256];
uint8_t values[256];
} HuffContext; } HuffContext;
/* common parameters used for decode_bigtree */ /* common parameters used for decode_bigtree */
@ -105,7 +108,7 @@ enum SmkBlockTypes {
* Can read SMKTREE_DECODE_MAX_RECURSION before the first check; * Can read SMKTREE_DECODE_MAX_RECURSION before the first check;
* does not overread gb on success. * does not overread gb on success.
*/ */
static int smacker_decode_tree(GetBitContext *gb, HuffContext *hc, uint32_t prefix, int length) static int smacker_decode_tree(GetBitContext *gb, HuffContext *hc, int length)
{ {
if (length > SMKTREE_DECODE_MAX_RECURSION || length > 3 * SMKTREE_BITS) { if (length > SMKTREE_DECODE_MAX_RECURSION || length > 3 * SMKTREE_BITS) {
av_log(NULL, AV_LOG_ERROR, "Maximum tree recursion level exceeded.\n"); av_log(NULL, AV_LOG_ERROR, "Maximum tree recursion level exceeded.\n");
@ -119,18 +122,15 @@ static int smacker_decode_tree(GetBitContext *gb, HuffContext *hc, uint32_t pref
} }
if (get_bits_left(gb) < 8) if (get_bits_left(gb) < 8)
return AVERROR_INVALIDDATA; return AVERROR_INVALIDDATA;
hc->bits[hc->current] = prefix; hc->entries[hc->current++] = (HuffEntry){ get_bits(gb, 8), length };
hc->lengths[hc->current] = length;
hc->values[hc->current] = get_bits(gb, 8);
hc->current++;
return 0; return 0;
} else { //Node } else { //Node
int r; int r;
length++; length++;
r = smacker_decode_tree(gb, hc, prefix, length); r = smacker_decode_tree(gb, hc, length);
if(r) if(r)
return r; return r;
return smacker_decode_tree(gb, hc, prefix | (1U << (length - 1)), length); return smacker_decode_tree(gb, hc, length);
} }
} }
@ -216,22 +216,21 @@ static int smacker_decode_header_tree(SmackVContext *smk, GetBitContext *gb, int
i ? "high" : "low"); i ? "high" : "low");
continue; continue;
} }
err = smacker_decode_tree(gb, &h, 0, 0); err = smacker_decode_tree(gb, &h, 0);
if (err < 0) if (err < 0)
goto error; goto error;
skip_bits1(gb); skip_bits1(gb);
if (h.current > 1) { if (h.current > 1) {
err = ff_init_vlc_sparse(&vlc[i], SMKTREE_BITS, h.current, err = ff_init_vlc_from_lengths(&vlc[i], SMKTREE_BITS, h.current,
h.lengths, sizeof(*h.lengths), sizeof(*h.lengths), &h.entries[0].length, sizeof(*h.entries),
h.bits, sizeof(*h.bits), sizeof(*h.bits), &h.entries[0].value, sizeof(*h.entries), 1,
h.values, sizeof(*h.values), sizeof(*h.values), 0, INIT_VLC_OUTPUT_LE, smk->avctx);
INIT_VLC_LE);
if (err < 0) { if (err < 0) {
av_log(smk->avctx, AV_LOG_ERROR, "Cannot build VLC table\n"); av_log(smk->avctx, AV_LOG_ERROR, "Cannot build VLC table\n");
goto error; goto error;
} }
} else } else
ctx.vals[i] = h.values[0]; ctx.vals[i] = h.entries[0].value;
} }
escapes[0] = get_bits(gb, 16); escapes[0] = get_bits(gb, 16);
@ -650,21 +649,20 @@ static int smka_decode_frame(AVCodecContext *avctx, void *data,
HuffContext h; HuffContext h;
h.current = 0; h.current = 0;
skip_bits1(&gb); skip_bits1(&gb);
if ((ret = smacker_decode_tree(&gb, &h, 0, 0)) < 0) if ((ret = smacker_decode_tree(&gb, &h, 0)) < 0)
goto error; goto error;
skip_bits1(&gb); skip_bits1(&gb);
if (h.current > 1) { if (h.current > 1) {
ret = ff_init_vlc_sparse(&vlc[i], SMKTREE_BITS, h.current, ret = ff_init_vlc_from_lengths(&vlc[i], SMKTREE_BITS, h.current,
h.lengths, sizeof(*h.lengths), sizeof(*h.lengths), &h.entries[0].length, sizeof(*h.entries),
h.bits, sizeof(*h.bits), sizeof(*h.bits), &h.entries[0].value, sizeof(*h.entries), 1,
h.values, sizeof(*h.values), sizeof(*h.values), 0, INIT_VLC_OUTPUT_LE, avctx);
INIT_VLC_LE);
if (ret < 0) { if (ret < 0) {
av_log(avctx, AV_LOG_ERROR, "Cannot build VLC table\n"); av_log(avctx, AV_LOG_ERROR, "Cannot build VLC table\n");
goto error; goto error;
} }
} else } else
values[i] = h.values[0]; values[i] = h.entries[0].value;
} }
/* this codec relies on wraparound instead of clipping audio */ /* this codec relies on wraparound instead of clipping audio */
if(bits) { //decode 16-bit data if(bits) { //decode 16-bit data