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avcodec/sheervideo: Improve creating VLC tables

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Don't needlessly copy an array around; don't create a table with
default symbols; and use smaller types to save stack space: The longest
code here is 16 bits, so one can store the codes in this type.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2020-10-10 06:13:21 +02:00
parent 11a6347f9e
commit 1bff2f3d92
1 changed files with 7 additions and 12 deletions
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19
libavcodec/sheervideo.c
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@ -1782,25 +1782,20 @@ static void decode_rgb(AVCodecContext *avctx, AVFrame *p, GetBitContext *gb)
static int build_vlc(VLC *vlc, const uint8_t *len, int count) static int build_vlc(VLC *vlc, const uint8_t *len, int count)
{ {
uint32_t codes[1024]; uint16_t codes[1024];
uint8_t bits[1024]; unsigned index;
uint16_t syms[1024];
uint64_t index;
int i; int i;
index = 0; index = 0;
for (i = 0; i < count; i++) { for (i = 0; i < count; i++) {
codes[i] = index >> (32 - len[i]); codes[i] = index >> (32 - len[i]);
bits[i] = len[i]; index += 1U << (32 - len[i]);
syms[i] = i;
index += 1ULL << (32 - len[i]);
} }
ff_free_vlc(vlc); ff_free_vlc(vlc);
return ff_init_vlc_sparse(vlc, 12, count, return init_vlc(vlc, 12, count,
bits, sizeof(*bits), sizeof(*bits), len, sizeof(*len), sizeof(*len),
codes, sizeof(*codes), sizeof(*codes), codes, sizeof(*codes), sizeof(*codes), 0);
syms, sizeof(*syms), sizeof(*syms), 0);
} }
static int decode_frame(AVCodecContext *avctx, static int decode_frame(AVCodecContext *avctx,