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avcodec/asvdec: Avoid reversing input data twice

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Up until now the ASV2 decoder used an ordinary big-endian bitreader to
read data actually destined for a little-endian bitreader; this is done
by reversing the whole input packet bitwise, using the big-endian
bigreader and reversing (and shifting) the result again. This commit
stops this and instead uses a little-endian bitreader directly.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2020-10-12 12:38:59 +02:00
parent 62073cfa97
commit cdf7619705
1 changed files with 44 additions and 33 deletions
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65
libavcodec/asvdec.c
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@ -31,7 +31,6 @@
#include "blockdsp.h" #include "blockdsp.h"
#include "idctdsp.h" #include "idctdsp.h"
#include "internal.h" #include "internal.h"
#include "mathops.h"
#include "mpeg12data.h" #include "mpeg12data.h"
#define CCP_VLC_BITS 5 #define CCP_VLC_BITS 5
@ -56,27 +55,24 @@ static av_cold void init_vlcs(ASV1Context *a)
INIT_VLC_STATIC(&ccp_vlc, CCP_VLC_BITS, 17, INIT_VLC_STATIC(&ccp_vlc, CCP_VLC_BITS, 17,
&ff_asv_ccp_tab[0][1], 2, 1, &ff_asv_ccp_tab[0][1], 2, 1,
&ff_asv_ccp_tab[0][0], 2, 1, 32); &ff_asv_ccp_tab[0][0], 2, 1, 32);
INIT_VLC_STATIC(&dc_ccp_vlc, DC_CCP_VLC_BITS, 8, INIT_CUSTOM_VLC_STATIC(&dc_ccp_vlc, DC_CCP_VLC_BITS, 8,
&ff_asv_dc_ccp_tab[0][1], 2, 1, &ff_asv_dc_ccp_tab[0][1], 2, 1,
&ff_asv_dc_ccp_tab[0][0], 2, 1, 16); &ff_asv_dc_ccp_tab[0][0], 2, 1,
INIT_VLC_STATIC(&ac_ccp_vlc, AC_CCP_VLC_BITS, 16, INIT_VLC_OUTPUT_LE, 16);
INIT_CUSTOM_VLC_STATIC(&ac_ccp_vlc, AC_CCP_VLC_BITS, 16,
&ff_asv_ac_ccp_tab[0][1], 2, 1, &ff_asv_ac_ccp_tab[0][1], 2, 1,
&ff_asv_ac_ccp_tab[0][0], 2, 1, 64); &ff_asv_ac_ccp_tab[0][0], 2, 1,
INIT_VLC_OUTPUT_LE, 64);
INIT_VLC_STATIC(&level_vlc, ASV1_LEVEL_VLC_BITS, 7, INIT_VLC_STATIC(&level_vlc, ASV1_LEVEL_VLC_BITS, 7,
&ff_asv_level_tab[0][1], 2, 1, &ff_asv_level_tab[0][1], 2, 1,
&ff_asv_level_tab[0][0], 2, 1, 16); &ff_asv_level_tab[0][0], 2, 1, 16);
INIT_VLC_STATIC(&asv2_level_vlc, ASV2_LEVEL_VLC_BITS, 63, INIT_CUSTOM_VLC_STATIC(&asv2_level_vlc, ASV2_LEVEL_VLC_BITS, 63,
&ff_asv2_level_tab[0][1], 2, 1, &ff_asv2_level_tab[0][1], 2, 1,
&ff_asv2_level_tab[0][0], 2, 1, 1024); &ff_asv2_level_tab[0][0], 2, 1,
INIT_VLC_OUTPUT_LE, 1024);
} }
} }
// FIXME write a reversed bitstream reader to avoid the double reverse
static inline int asv2_get_bits(GetBitContext *gb, int n)
{
return ff_reverse[get_bits(gb, n) << (8 - n)];
}
static inline int asv1_get_level(GetBitContext *gb) static inline int asv1_get_level(GetBitContext *gb)
{ {
int code = get_vlc2(gb, level_vlc.table, ASV1_LEVEL_VLC_BITS, 1); int code = get_vlc2(gb, level_vlc.table, ASV1_LEVEL_VLC_BITS, 1);
@ -87,12 +83,31 @@ static inline int asv1_get_level(GetBitContext *gb)
return code - 3; return code - 3;
} }
// get_vlc2() is big-endian in this file
static inline int asv2_get_vlc2(GetBitContext *gb, VLC_TYPE (*table)[2], int bits)
{
unsigned int index;
int code, n;
OPEN_READER(re, gb);
UPDATE_CACHE_LE(re, gb);
index = SHOW_UBITS_LE(re, gb, bits);
code = table[index][0];
n = table[index][1];
LAST_SKIP_BITS(re, gb, n);
CLOSE_READER(re, gb);
return code;
}
static inline int asv2_get_level(GetBitContext *gb) static inline int asv2_get_level(GetBitContext *gb)
{ {
int code = get_vlc2(gb, asv2_level_vlc.table, ASV2_LEVEL_VLC_BITS, 1); int code = asv2_get_vlc2(gb, asv2_level_vlc.table, ASV2_LEVEL_VLC_BITS);
if (code == 31) if (code == 31)
return (int8_t) asv2_get_bits(gb, 8); return (int8_t) get_bits_le(gb, 8);
else else
return code - 31; return code - 31;
} }
@ -132,11 +147,11 @@ static inline int asv2_decode_block(ASV1Context *a, int16_t block[64])
{ {
int i, count, ccp; int i, count, ccp;
count = asv2_get_bits(&a->gb, 4); count = get_bits_le(&a->gb, 4);
block[0] = 8 * asv2_get_bits(&a->gb, 8); block[0] = 8 * get_bits_le(&a->gb, 8);
ccp = get_vlc2(&a->gb, dc_ccp_vlc.table, DC_CCP_VLC_BITS, 1); ccp = asv2_get_vlc2(&a->gb, dc_ccp_vlc.table, DC_CCP_VLC_BITS);
if (ccp) { if (ccp) {
if (ccp & 4) if (ccp & 4)
block[a->scantable.permutated[1]] = (asv2_get_level(&a->gb) * a->intra_matrix[1]) >> 4; block[a->scantable.permutated[1]] = (asv2_get_level(&a->gb) * a->intra_matrix[1]) >> 4;
@ -147,7 +162,7 @@ static inline int asv2_decode_block(ASV1Context *a, int16_t block[64])
} }
for (i = 1; i < count + 1; i++) { for (i = 1; i < count + 1; i++) {
const int ccp = get_vlc2(&a->gb, ac_ccp_vlc.table, AC_CCP_VLC_BITS, 1); const int ccp = asv2_get_vlc2(&a->gb, ac_ccp_vlc.table, AC_CCP_VLC_BITS);
if (ccp) { if (ccp) {
if (ccp & 8) if (ccp & 8)
@ -221,21 +236,18 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
p->pict_type = AV_PICTURE_TYPE_I; p->pict_type = AV_PICTURE_TYPE_I;
p->key_frame = 1; p->key_frame = 1;
if (avctx->codec_id == AV_CODEC_ID_ASV1) {
av_fast_padded_malloc(&a->bitstream_buffer, &a->bitstream_buffer_size, av_fast_padded_malloc(&a->bitstream_buffer, &a->bitstream_buffer_size,
buf_size); buf_size);
if (!a->bitstream_buffer) if (!a->bitstream_buffer)
return AVERROR(ENOMEM); return AVERROR(ENOMEM);
if (avctx->codec_id == AV_CODEC_ID_ASV1) {
a->bbdsp.bswap_buf((uint32_t *) a->bitstream_buffer, a->bbdsp.bswap_buf((uint32_t *) a->bitstream_buffer,
(const uint32_t *) buf, buf_size / 4); (const uint32_t *) buf, buf_size / 4);
} else {
int i;
for (i = 0; i < buf_size; i++)
a->bitstream_buffer[i] = ff_reverse[buf[i]];
}
ret = init_get_bits8(&a->gb, a->bitstream_buffer, buf_size); ret = init_get_bits8(&a->gb, a->bitstream_buffer, buf_size);
} else {
ret = init_get_bits8_le(&a->gb, buf, buf_size);
}
if (ret < 0) if (ret < 0)
return ret; return ret;
@ -342,7 +354,6 @@ AVCodec ff_asv2_decoder = {
.id = AV_CODEC_ID_ASV2, .id = AV_CODEC_ID_ASV2,
.priv_data_size = sizeof(ASV1Context), .priv_data_size = sizeof(ASV1Context),
.init = decode_init, .init = decode_init,
.close = decode_end,
.decode = decode_frame, .decode = decode_frame,
.capabilities = AV_CODEC_CAP_DR1, .capabilities = AV_CODEC_CAP_DR1,
}; };