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FFmpeg/libavcodec/mpeg12.c
Andreas Rheinhardt c4990409f2 avcodec/mpeg12: Reduce size of motion-vector VLC 
It currently uses 9 bits per table, but there are no codes with
nine bits at all, while there are codes with eight, ten and eleven bits.
So reducing the table size to eight bits will not reduce the amount of
codes that can be parsed in the first step, but it allows to reduce the
size of the motion-vector VLC.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
2020-10-12 02:00:08 +02:00

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/*
* MPEG-1/2 decoder
* Copyright (c) 2000, 2001 Fabrice Bellard
* Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* MPEG-1/2 decoder
*/
#define UNCHECKED_BITSTREAM_READER 1
#include "libavutil/attributes.h"
#include "libavutil/avassert.h"
#include "libavutil/timecode.h"
#include "internal.h"
#include "avcodec.h"
#include "mpegvideo.h"
#include "error_resilience.h"
#include "mpeg12.h"
#include "mpeg12data.h"
#include "mpegvideodata.h"
#include "bytestream.h"
#include "thread.h"
uint8_t ff_mpeg12_static_rl_table_store[2][2][2*MAX_RUN + MAX_LEVEL + 3];
static const uint8_t table_mb_ptype[7][2] = {
{ 3, 5 }, // 0x01 MB_INTRA
{ 1, 2 }, // 0x02 MB_PAT
{ 1, 3 }, // 0x08 MB_FOR
{ 1, 1 }, // 0x0A MB_FOR|MB_PAT
{ 1, 6 }, // 0x11 MB_QUANT|MB_INTRA
{ 1, 5 }, // 0x12 MB_QUANT|MB_PAT
{ 2, 5 }, // 0x1A MB_QUANT|MB_FOR|MB_PAT
};
static const uint8_t table_mb_btype[11][2] = {
{ 3, 5 }, // 0x01 MB_INTRA
{ 2, 3 }, // 0x04 MB_BACK
{ 3, 3 }, // 0x06 MB_BACK|MB_PAT
{ 2, 4 }, // 0x08 MB_FOR
{ 3, 4 }, // 0x0A MB_FOR|MB_PAT
{ 2, 2 }, // 0x0C MB_FOR|MB_BACK
{ 3, 2 }, // 0x0E MB_FOR|MB_BACK|MB_PAT
{ 1, 6 }, // 0x11 MB_QUANT|MB_INTRA
{ 2, 6 }, // 0x16 MB_QUANT|MB_BACK|MB_PAT
{ 3, 6 }, // 0x1A MB_QUANT|MB_FOR|MB_PAT
{ 2, 5 }, // 0x1E MB_QUANT|MB_FOR|MB_BACK|MB_PAT
};
av_cold void ff_init_2d_vlc_rl(RLTable *rl, unsigned static_size, int flags)
{
int i;
VLC_TYPE table[680][2] = {{0}};
VLC vlc = { .table = table, .table_allocated = static_size };
av_assert0(static_size <= FF_ARRAY_ELEMS(table));
init_vlc(&vlc, TEX_VLC_BITS, rl->n + 2, &rl->table_vlc[0][1], 4, 2, &rl->table_vlc[0][0], 4, 2, INIT_VLC_USE_NEW_STATIC | flags);
for (i = 0; i < vlc.table_size; i++) {
int code = vlc.table[i][0];
int len = vlc.table[i][1];
int level, run;
if (len == 0) { // illegal code
run = 65;
level = MAX_LEVEL;
} else if (len<0) { //more bits needed
run = 0;
level = code;
} else {
if (code == rl->n) { //esc
run = 65;
level = 0;
} else if (code == rl->n+1) { //eob
run = 0;
level = 127;
} else {
run = rl->table_run [code] + 1;
level = rl->table_level[code];
}
}
rl->rl_vlc[0][i].len = len;
rl->rl_vlc[0][i].level = level;
rl->rl_vlc[0][i].run = run;
}
}
av_cold void ff_mpeg12_common_init(MpegEncContext *s)
{
s->y_dc_scale_table =
s->c_dc_scale_table = ff_mpeg2_dc_scale_table[s->intra_dc_precision];
}
void ff_mpeg1_clean_buffers(MpegEncContext *s)
{
s->last_dc[0] = 1 << (7 + s->intra_dc_precision);
s->last_dc[1] = s->last_dc[0];
s->last_dc[2] = s->last_dc[0];
memset(s->last_mv, 0, sizeof(s->last_mv));
}
/******************************************/
/* decoding */
VLC ff_mv_vlc;
VLC ff_dc_lum_vlc;
VLC ff_dc_chroma_vlc;
VLC ff_mbincr_vlc;
VLC ff_mb_ptype_vlc;
VLC ff_mb_btype_vlc;
VLC ff_mb_pat_vlc;
av_cold void ff_mpeg12_init_vlcs(void)
{
static int done = 0;
if (!done) {
done = 1;
INIT_VLC_STATIC(&ff_dc_lum_vlc, DC_VLC_BITS, 12,
ff_mpeg12_vlc_dc_lum_bits, 1, 1,
ff_mpeg12_vlc_dc_lum_code, 2, 2, 512);
INIT_VLC_STATIC(&ff_dc_chroma_vlc, DC_VLC_BITS, 12,
ff_mpeg12_vlc_dc_chroma_bits, 1, 1,
ff_mpeg12_vlc_dc_chroma_code, 2, 2, 514);
INIT_VLC_STATIC(&ff_mv_vlc, MV_VLC_BITS, 17,
&ff_mpeg12_mbMotionVectorTable[0][1], 2, 1,
&ff_mpeg12_mbMotionVectorTable[0][0], 2, 1, 266);
INIT_VLC_STATIC(&ff_mbincr_vlc, MBINCR_VLC_BITS, 36,
&ff_mpeg12_mbAddrIncrTable[0][1], 2, 1,
&ff_mpeg12_mbAddrIncrTable[0][0], 2, 1, 538);
INIT_VLC_STATIC(&ff_mb_pat_vlc, MB_PAT_VLC_BITS, 64,
&ff_mpeg12_mbPatTable[0][1], 2, 1,
&ff_mpeg12_mbPatTable[0][0], 2, 1, 512);
INIT_VLC_STATIC(&ff_mb_ptype_vlc, MB_PTYPE_VLC_BITS, 7,
&table_mb_ptype[0][1], 2, 1,
&table_mb_ptype[0][0], 2, 1, 64);
INIT_VLC_STATIC(&ff_mb_btype_vlc, MB_BTYPE_VLC_BITS, 11,
&table_mb_btype[0][1], 2, 1,
&table_mb_btype[0][0], 2, 1, 64);
ff_rl_init(&ff_rl_mpeg1, ff_mpeg12_static_rl_table_store[0]);
ff_rl_init(&ff_rl_mpeg2, ff_mpeg12_static_rl_table_store[1]);
INIT_2D_VLC_RL(ff_rl_mpeg1, 680, 0);
INIT_2D_VLC_RL(ff_rl_mpeg2, 674, 0);
}
}
/**
* Find the end of the current frame in the bitstream.
* @return the position of the first byte of the next frame, or -1
*/
int ff_mpeg1_find_frame_end(ParseContext *pc, const uint8_t *buf, int buf_size, AVCodecParserContext *s)
{
int i;
uint32_t state = pc->state;
/* EOF considered as end of frame */
if (buf_size == 0)
return 0;
/*
0 frame start -> 1/4
1 first_SEQEXT -> 0/2
2 first field start -> 3/0
3 second_SEQEXT -> 2/0
4 searching end
*/
for (i = 0; i < buf_size; i++) {
av_assert1(pc->frame_start_found >= 0 && pc->frame_start_found <= 4);
if (pc->frame_start_found & 1) {
if (state == EXT_START_CODE && (buf[i] & 0xF0) != 0x80)
pc->frame_start_found--;
else if (state == EXT_START_CODE + 2) {
if ((buf[i] & 3) == 3)
pc->frame_start_found = 0;
else
pc->frame_start_found = (pc->frame_start_found + 1) & 3;
}
state++;
} else {
i = avpriv_find_start_code(buf + i, buf + buf_size, &state) - buf - 1;
if (pc->frame_start_found == 0 && state >= SLICE_MIN_START_CODE && state <= SLICE_MAX_START_CODE) {
i++;
pc->frame_start_found = 4;
}
if (state == SEQ_END_CODE) {
pc->frame_start_found = 0;
pc->state=-1;
return i+1;
}
if (pc->frame_start_found == 2 && state == SEQ_START_CODE)
pc->frame_start_found = 0;
if (pc->frame_start_found < 4 && state == EXT_START_CODE)
pc->frame_start_found++;
if (pc->frame_start_found == 4 && (state & 0xFFFFFF00) == 0x100) {
if (state < SLICE_MIN_START_CODE || state > SLICE_MAX_START_CODE) {
pc->frame_start_found = 0;
pc->state = -1;
return i - 3;
}
}
if (pc->frame_start_found == 0 && s && state == PICTURE_START_CODE) {
ff_fetch_timestamp(s, i - 3, 1, i > 3);
}
}
}
pc->state = state;
return END_NOT_FOUND;
}
#define MAX_INDEX (64 - 1)
int ff_mpeg1_decode_block_intra(GetBitContext *gb,
const uint16_t *quant_matrix,
uint8_t *const scantable, int last_dc[3],
int16_t *block, int index, int qscale)
{
int dc, diff, i = 0, component;
RLTable *rl = &ff_rl_mpeg1;
/* DC coefficient */
component = index <= 3 ? 0 : index - 4 + 1;
diff = decode_dc(gb, component);
if (diff >= 0xffff)
return AVERROR_INVALIDDATA;
dc = last_dc[component];
dc += diff;
last_dc[component] = dc;
block[0] = dc * quant_matrix[0];
{
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
if (((int32_t)GET_CACHE(re, gb)) <= (int32_t)0xBFFFFFFF)
goto end;
/* now quantify & encode AC coefficients */
while (1) {
int level, run, j;
GET_RL_VLC(level, run, re, gb, rl->rl_vlc[0],
TEX_VLC_BITS, 2, 0);
if (level != 0) {
i += run;
if (i > MAX_INDEX)
break;
j = scantable[i];
level = (level * qscale * quant_matrix[j]) >> 4;
level = (level - 1) | 1;
level = (level ^ SHOW_SBITS(re, gb, 1)) -
SHOW_SBITS(re, gb, 1);
SKIP_BITS(re, gb, 1);
} else {
/* escape */
run = SHOW_UBITS(re, gb, 6) + 1;
LAST_SKIP_BITS(re, gb, 6);
UPDATE_CACHE(re, gb);
level = SHOW_SBITS(re, gb, 8);
SKIP_BITS(re, gb, 8);
if (level == -128) {
level = SHOW_UBITS(re, gb, 8) - 256;
SKIP_BITS(re, gb, 8);
} else if (level == 0) {
level = SHOW_UBITS(re, gb, 8);
SKIP_BITS(re, gb, 8);
}
i += run;
if (i > MAX_INDEX)
break;
j = scantable[i];
if (level < 0) {
level = -level;
level = (level * qscale * quant_matrix[j]) >> 4;
level = (level - 1) | 1;
level = -level;
} else {
level = (level * qscale * quant_matrix[j]) >> 4;
level = (level - 1) | 1;
}
}
block[j] = level;
if (((int32_t)GET_CACHE(re, gb)) <= (int32_t)0xBFFFFFFF)
break;
UPDATE_CACHE(re, gb);
}
end:
LAST_SKIP_BITS(re, gb, 2);
CLOSE_READER(re, gb);
}
if (i > MAX_INDEX)
i = AVERROR_INVALIDDATA;
return i;
}
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