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Code Issues Releases Activity

avcodec/vlc, bitstream: Allow to use BE codes to initialize LE VLC

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This is easily possible because ff_init_vlc_sparse() already transforms
both LE as well as BE codes to a normal form internally before
processing them further. This will be used in subsequent commits.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2020-10-12 05:24:42 +02:00
parent e78bbbc2b1
commit 9eb7d8b45d
2 changed files with 22 additions and 13 deletions
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6
libavcodec/bitstream.c
View File

@ -182,7 +182,7 @@ static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
j = code >> (32 - table_nb_bits);
nb = 1 << (table_nb_bits - n);
inc = 1;
if (flags & INIT_VLC_LE) {
if (flags & INIT_VLC_OUTPUT_LE) {
j = bitswap_32(code);
inc = 1 << n;
}
@ -217,7 +217,7 @@ static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
subtable_bits = FFMAX(subtable_bits, n);
}
subtable_bits = FFMIN(subtable_bits, table_nb_bits);
j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
j = (flags & INIT_VLC_OUTPUT_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
table[j][1] = -subtable_bits;
ff_dlog(NULL, "%4x: n=%d (subtable)\n",
j, codes[i].bits + table_nb_bits);
@ -319,7 +319,7 @@ int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,
av_free(buf); \
return AVERROR(EINVAL); \
} \
if (flags & INIT_VLC_LE) \
if (flags & INIT_VLC_INPUT_LE) \
buf[j].code = bitswap_32(buf[j].code); \
else \
buf[j].code <<= 32 - buf[j].bits; \

29
libavcodec/vlc.h
View File

@ -51,26 +51,35 @@ int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
int flags);
void ff_free_vlc(VLC *vlc);
#define INIT_VLC_LE 2
/* If INIT_VLC_INPUT_LE is set, the LSB bit of the codes used to
* initialize the VLC table is the first bit to be read. */
#define INIT_VLC_INPUT_LE 2
/* If set the VLC is intended for a little endian bitstream reader. */
#define INIT_VLC_OUTPUT_LE 8
#define INIT_VLC_LE (INIT_VLC_INPUT_LE | INIT_VLC_OUTPUT_LE)
#define INIT_VLC_USE_NEW_STATIC 4
#define INIT_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, h, i, j, static_size) \
#define INIT_CUSTOM_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
h, i, j, flags, static_size) \
do { \
static VLC_TYPE table[static_size][2]; \
(vlc)->table = table; \
(vlc)->table_allocated = static_size; \
ff_init_vlc_sparse(vlc, bits, a, b, c, d, e, f, g, h, i, j, \
INIT_VLC_USE_NEW_STATIC); \
flags | INIT_VLC_USE_NEW_STATIC); \
} while (0)
#define INIT_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, h, i, j, static_size) \
INIT_CUSTOM_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
h, i, j, 0, static_size)
#define INIT_LE_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, h, i, j, static_size) \
do { \
static VLC_TYPE table[static_size][2]; \
(vlc)->table = table; \
(vlc)->table_allocated = static_size; \
ff_init_vlc_sparse(vlc, bits, a, b, c, d, e, f, g, h, i, j, \
INIT_VLC_USE_NEW_STATIC | INIT_VLC_LE); \
} while (0)
INIT_CUSTOM_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
h, i, j, INIT_VLC_LE, static_size)
#define INIT_CUSTOM_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, flags, static_size) \
INIT_CUSTOM_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
NULL, 0, 0, flags, static_size)
#define INIT_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
INIT_VLC_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, NULL, 0, 0, static_size)