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/*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef AVCODEC_VLC_H
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#define AVCODEC_VLC_H
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#include <stdint.h>
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#define VLC_MULTI_MAX_SYMBOLS 6
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// When changing this, be sure to also update tableprint_vlc.h accordingly.
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typedef int16_t VLCBaseType;
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typedef struct VLCElem {
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VLCBaseType sym, len;
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} VLCElem;
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typedef struct VLC {
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int bits;
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VLCElem *table;
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int table_size, table_allocated;
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} VLC;
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typedef struct VLC_MULTI_ELEM {
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uint8_t val[VLC_MULTI_MAX_SYMBOLS];
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int8_t len; // -31,32
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uint8_t num;
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} VLC_MULTI_ELEM;
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typedef struct VLC_MULTI {
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VLC_MULTI_ELEM *table;
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int table_size, table_allocated;
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} VLC_MULTI;
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typedef struct RL_VLC_ELEM {
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int16_t level;
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int8_t len;
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uint8_t run;
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} RL_VLC_ELEM;
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#define vlc_init(vlc, nb_bits, nb_codes, \
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bits, bits_wrap, bits_size, \
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codes, codes_wrap, codes_size, \
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flags) \
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ff_vlc_init_sparse(vlc, nb_bits, nb_codes, \
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bits, bits_wrap, bits_size, \
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codes, codes_wrap, codes_size, \
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NULL, 0, 0, flags)
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/**
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* Build VLC decoding tables suitable for use with get_vlc2().
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*
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* @param[in,out] vlc The VLC to be initialized; table and table_allocated
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* must have been set when initializing a static VLC,
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* otherwise this will be treated as uninitialized.
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* @param[in] nb_bits The number of bits to use for the VLC table;
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* higher values take up more memory and cache, but
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* allow to read codes with fewer reads.
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* Corresponds to the `bits` parameter of get_vlc2().
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* @param[in] nb_codes The number of provided bits, codes and (if supplied)
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* symbol entries.
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* @param[in] bits The lengths (in bits) of the codes. Entries > 0
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* correspond to valid codes; entries == 0 will be skipped.
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* @param[in] bits_wrap Stride (in bytes) of the bits table.
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* @param[in] codes_size Size of the bits. 1, 2 and 4 are supported.
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* @param[in] codes Table which gives the bit pattern of of each vlc code.
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* @param[in] codes_wrap Stride (in bytes) of the codes table.
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* @param[in] codes_size Size of the codes. 1, 2 and 4 are supported.
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* @param[in] symbols The symbols, i.e. what is returned from get_vlc2()
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* when the corresponding code is encountered.
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* May be NULL, then 0, 1, 2, 3, 4,... will be used.
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* @param[in] symbols_wrap Stride (in bytes) of the symbols table.
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* @param[in] symbols_size Size of the symbols. 1 and 2 are supported.
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* @param[in] flags A combination of the VLC_INIT_* flags.
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*
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* 'wrap' and 'size' make it possible to use any memory configuration and types
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* (byte/word/int) to store the 'bits', 'codes', and 'symbols' tables.
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*/
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int ff_vlc_init_sparse(VLC *vlc, int nb_bits, int nb_codes,
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const void *bits, int bits_wrap, int bits_size,
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const void *codes, int codes_wrap, int codes_size,
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const void *symbols, int symbols_wrap, int symbols_size,
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int flags);
|
avcodec/bitstream: Add second function to create VLCs
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.
This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.
Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.
This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.
In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.
Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
4 years ago
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/**
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* Build VLC decoding tables suitable for use with get_vlc2()
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*
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* This function takes lengths and symbols and calculates the codes from them.
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* For this the input lengths and symbols have to be sorted according to "left
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* nodes in the corresponding tree first".
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*
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* @param[in,out] vlc The VLC to be initialized; table and table_allocated
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* must have been set when initializing a static VLC,
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* otherwise this will be treated as uninitialized.
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* @param[in] nb_bits The number of bits to use for the VLC table;
|
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* higher values take up more memory and cache, but
|
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|
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* allow to read codes with fewer reads.
|
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* @param[in] nb_codes The number of provided length and (if supplied) symbol
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* entries.
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* @param[in] lens The lengths of the codes. Entries > 0 correspond to
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* valid codes; entries == 0 will be skipped and entries
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* with len < 0 indicate that the tree is incomplete and
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* has an open end of length -len at this position.
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* @param[in] lens_wrap Stride (in bytes) of the lengths.
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* @param[in] symbols The symbols, i.e. what is returned from get_vlc2()
|
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* when the corresponding code is encountered.
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* May be NULL, then 0, 1, 2, 3, 4,... will be used.
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* @param[in] symbols_wrap Stride (in bytes) of the symbols.
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* @param[in] symbols_size Size of the symbols. 1 and 2 are supported.
|
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* @param[in] offset An offset to apply to all the valid symbols.
|
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|
|
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* @param[in] flags A combination of the VLC_INIT_* flags; notice that
|
|
|
|
|
* VLC_INIT_INPUT_LE is pointless and ignored.
|
avcodec/bitstream: Add second function to create VLCs
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.
This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.
Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.
This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.
In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.
Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
4 years ago
|
|
|
*/
|
|
|
|
|
int ff_vlc_init_from_lengths(VLC *vlc, int nb_bits, int nb_codes,
|
avcodec/bitstream: Add second function to create VLCs
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.
This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.
Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.
This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.
In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.
Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
4 years ago
|
|
|
const int8_t *lens, int lens_wrap,
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|
|
|
|
const void *symbols, int symbols_wrap, int symbols_size,
|
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|
|
|
int offset, int flags, void *logctx);
|
|
|
|
|
|
|
|
|
|
/**
|
|
|
|
|
* Build VLC decoding tables suitable for use with get_vlc_multi()
|
|
|
|
|
*
|
|
|
|
|
* This function takes lengths and symbols and calculates the codes from them.
|
|
|
|
|
* For this the input lengths and symbols have to be sorted according to "left
|
|
|
|
|
* nodes in the corresponding tree first".
|
|
|
|
|
*
|
|
|
|
|
* @param[in,out] vlc The VLC to be initialized; table and table_allocated
|
|
|
|
|
* must have been set when initializing a static VLC,
|
|
|
|
|
* otherwise this will be treated as uninitialized.
|
|
|
|
|
* @param[in,out] multi The VLC_MULTI to be initialized; table and table_allocated
|
|
|
|
|
* must have been set when initializing a static VLC,
|
|
|
|
|
* otherwise this will be treated as uninitialized.
|
|
|
|
|
* @param[in] nb_bits The number of bits to use for the VLC table;
|
|
|
|
|
* higher values take up more memory and cache, but
|
|
|
|
|
* allow to read codes with fewer reads.
|
|
|
|
|
* @param[in] nb_elems The max possible number of elements.
|
|
|
|
|
* @param[in] nb_codes The number of provided length and (if supplied) symbol
|
|
|
|
|
* entries.
|
|
|
|
|
* @param[in] lens The lengths of the codes. Entries > 0 correspond to
|
|
|
|
|
* valid codes; entries == 0 will be skipped and entries
|
|
|
|
|
* with len < 0 indicate that the tree is incomplete and
|
|
|
|
|
* has an open end of length -len at this position.
|
|
|
|
|
* @param[in] lens_wrap Stride (in bytes) of the lengths.
|
|
|
|
|
* @param[in] symbols The symbols, i.e. what is returned from get_vlc2()
|
|
|
|
|
* when the corresponding code is encountered.
|
|
|
|
|
* May be NULL, then 0, 1, 2, 3, 4,... will be used.
|
|
|
|
|
* @param[in] symbols_wrap Stride (in bytes) of the symbols.
|
|
|
|
|
* @param[in] symbols_size Size of the symbols. 1 and 2 are supported.
|
|
|
|
|
* @param[in] offset An offset to apply to all the valid symbols.
|
|
|
|
|
* @param[in] flags A combination of the VLC_INIT_* flags; notice that
|
|
|
|
|
* VLC_INIT_INPUT_LE is pointless and ignored.
|
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|
|
|
*/
|
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|
|
int ff_vlc_init_multi_from_lengths(VLC *vlc, VLC_MULTI *multi, int nb_bits, int nb_elems,
|
|
|
|
|
int nb_codes, const int8_t *lens, int lens_wrap,
|
|
|
|
|
const void *symbols, int symbols_wrap, int symbols_size,
|
|
|
|
|
int offset, int flags, void *logctx);
|
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|
void ff_vlc_free_multi(VLC_MULTI *vlc);
|
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|
|
void ff_vlc_free(VLC *vlc);
|
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|
|
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|
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|
|
|
#define VLC_INIT_USE_STATIC 1
|
|
|
|
|
#define VLC_INIT_STATIC_OVERLONG (2 | VLC_INIT_USE_STATIC)
|
|
|
|
|
/* If VLC_INIT_INPUT_LE is set, the LSB bit of the codes used to
|
|
|
|
|
* initialize the VLC table is the first bit to be read. */
|
|
|
|
|
#define VLC_INIT_INPUT_LE 4
|
|
|
|
|
/* If set the VLC is intended for a little endian bitstream reader. */
|
|
|
|
|
#define VLC_INIT_OUTPUT_LE 8
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|
|
|
#define VLC_INIT_LE (VLC_INIT_INPUT_LE | VLC_INIT_OUTPUT_LE)
|
|
|
|
|
|
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|
|
|
#define VLC_INIT_CUSTOM_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
|
|
|
|
|
h, i, j, flags, static_size) \
|
|
|
|
|
do { \
|
|
|
|
|
static VLCElem table[static_size]; \
|
|
|
|
|
(vlc)->table = table; \
|
|
|
|
|
(vlc)->table_allocated = static_size; \
|
|
|
|
|
ff_vlc_init_sparse(vlc, bits, a, b, c, d, e, f, g, h, i, j, \
|
|
|
|
|
flags | VLC_INIT_USE_STATIC); \
|
|
|
|
|
} while (0)
|
|
|
|
|
|
|
|
|
|
#define VLC_INIT_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, h, i, j, static_size) \
|
|
|
|
|
VLC_INIT_CUSTOM_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
|
|
|
|
|
h, i, j, 0, static_size)
|
|
|
|
|
|
|
|
|
|
#define VLC_INIT_LE_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, h, i, j, static_size) \
|
|
|
|
|
VLC_INIT_CUSTOM_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
|
|
|
|
|
h, i, j, VLC_INIT_LE, static_size)
|
|
|
|
|
|
|
|
|
|
#define VLC_INIT_CUSTOM_STATIC(vlc, bits, a, b, c, d, e, f, g, flags, static_size) \
|
|
|
|
|
VLC_INIT_CUSTOM_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, \
|
|
|
|
|
NULL, 0, 0, flags, static_size)
|
|
|
|
|
|
|
|
|
|
#define VLC_INIT_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
|
|
|
|
|
VLC_INIT_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, NULL, 0, 0, static_size)
|
|
|
|
|
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|
|
#define VLC_INIT_LE_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
|
|
|
|
|
VLC_INIT_LE_SPARSE_STATIC(vlc, bits, a, b, c, d, e, f, g, NULL, 0, 0, static_size)
|
|
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|
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#define VLC_INIT_STATIC_FROM_LENGTHS(vlc, bits, nb_codes, lens, len_wrap, \
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avcodec/bitstream: Add second function to create VLCs
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.
This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.
Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.
This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.
In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.
Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
4 years ago
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symbols, symbols_wrap, symbols_size, \
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offset, flags, static_size) \
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do { \
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static VLCElem table[static_size]; \
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avcodec/bitstream: Add second function to create VLCs
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.
This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.
Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.
This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.
In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.
Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
4 years ago
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(vlc)->table = table; \
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(vlc)->table_allocated = static_size; \
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ff_vlc_init_from_lengths(vlc, bits, nb_codes, lens, len_wrap, \
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avcodec/bitstream: Add second function to create VLCs
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.
This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.
Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.
This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.
In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.
Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
4 years ago
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symbols, symbols_wrap, symbols_size, \
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offset, flags | VLC_INIT_USE_STATIC, \
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avcodec/bitstream: Add second function to create VLCs
When using ff_init_vlc_sparse() to create a VLC, three input tables are
used: A table for lengths, one for codes and one for symbols; the latter
one can be omitted, then a default one will be used. These input tables
will be traversed twice, once to get the long codes (which will be put
into subtables) and once for the small codes. The long codes are then
sorted so that entries that should be in the same subtable are
contiguous.
This commit adds an alternative to ff_init_vlc_sparse():
ff_init_vlc_from_lengths(). It is based upon the observation that if
lengths, codes and symbols tables are permuted (in the same way) so that
the codes are ordered from left to right in the corresponding tree and
if said tree is complete (i.e. every non-leaf node has two children),
the codes can be easily computed from the lengths and are therefore
redundant. This means that if one initializes such a VLC with explicitly
coded lengths, codes and symbols, the codes can be avoided; and even if
one has no explicitly coded symbols, it might still be beneficial to
remove the codes even when one has to add a new symbol table, because
codes are typically longer than symbols so that the latter often fit
into a smaller type, saving space.
Furthermore, given that the codes here are by definition ordered from
left to right, it is unnecessary to sort them again; for the same
reason, one does not have to traverse the input twice. This function
proved to be faster than ff_init_vlc_sparse() whenever it has been
benchmarked.
This function is usable for static tables (they can simply be permuted
once) as well as in scenarios where the tables are naturally ordered
from left to right in the tree; the latter e.g. happens with Smacker,
Theora and several other formats.
In order to make it also usable for (static) tables with incomplete trees,
negative lengths are used to indicate that there is an open end of a
certain length.
Finally, ff_init_vlc_from_lengths() has one downside compared to
ff_init_vlc_sparse(): The latter uses tables that can be reused by
encoders. Of course, one could calculate the needed table at runtime
if one so wishes, but it is nevertheless an obstacle.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
4 years ago
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NULL); \
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} while (0)
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#endif /* AVCODEC_VLC_H */
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