ATRAC3+ uses VLCs whose code lengths are ascending from left to right in
the tree; ergo it is possible (and done) to run-length encode the
lengths into so-called codebooks. These codebooks were variable-sized:
The first byte contained the minimum length of a code, the second the
maximum length; this was followed by max - min + 1 bytes containing the
actual numbers. The minimal min was 1, the maximal max 12.
While one saves a few bytes by only containing the range that is
actually used, this is more than offset by the fact that there needs
to be a pointer to each of these codebooks.
Furthermore, since 5f8de7b741 the content
of the Atrac3pSpecCodeTab structure (containing data for spectrum
decoding) can be cleanly separated into fields that are only used during
initialization and fields used during actual decoding: The pointers to
the codebooks and the field indicating whether an earlier codebook should
be reused constitute the former category. Therefore the new codebooks are
not placed into the Atrac3pSpecCodeTab (which is now unused during
init), but in an array of its own. The information whether an earlier
codebook should be reused is encoded in the first number of each
spectrum codebook: If it is negative, an earlier codebook (given by the
number) should be reused.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This allows to remove lots of pointers (130) to small symbol tables;
it has the downside that some of the default tables must now be coded
explicitly, but this costs only 6 + 4 + 8 + 16 + 8 bytes and is therefore
dwarfed by the gains.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
The earlier code used several different offset parameters that were
initialized to magic values. This is unnecessary.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
The ATRAC3+ decoder currently uses ff_init_vlc_sparse() to initialize
several VLCs; sometimes a symbols table is used, sometimes not; some of
the codes tables are uint16_t, some are uint8_t. Because of these two
latter facts it makes sense to switch to ff_init_vlc_from_lengths()
because it allows to remove the codes at the cost of adding symbols
tables of type uint8_t in the cases where there were none before.
Notice that sometimes the same codes and lengths tables were reused with
two different symbols tables; this could have been preserved (meaning
one could use a lengths table twice), but hasn't, because this allows
to use only one pointer to both the symbols and lengths instead of two
pointers.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
ff_init_vlc_from_lengths() can be used to offload the computation
of the codes; it also allows to omit the check whether the codes
are already properly ordered (they are). In this case, this also allows
to avoid the allocation of the buffer for the codes.
This improves performance: The amount of decicycles for one call to
tm2_build_huff_tables() when decoding tm20.avi from the FATE-suite
decreased from 46239 to 40035. This test consisted of looping 50 times
over the file and iterating the test ten times.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Switching from ff_init_vlc_sparse() to ff_init_vlc_from_lengths()
allows to replace codes which are so long that they need to be stored
in an uint16_t by symbols which fit into an uint8_t; and even these can
be avoided in case of the sprite trajectory VLC.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Switching from ff_init_vlc_sparse() to ff_init_vlc_from_lengths()
allows to replace codes which are so long that they need to be stored
in an uint16_t by symbols which fit into an uint8_t; furthermore, it is
also easily possible to already incorporate the offset (the real range
of Indeo 2 symbols starts at one, not zero) into the symbols.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
ff_init_vlc_from_lengths() can be used to offload the computation
of the codes; it also allows to omit the check whether the codes
are already properly ordered (they are).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
ff_init_vlc_from_lengths() can be used to offload the computation
of the codes; it also needn't check whether the codes are already
properly ordered (they are).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
The lengths of the codes used by the mss4 decoder are ascending from
left to right and therefore the lengths can be run-length encoded and
the codes can be easily derived from them. And this is how it is indeed
done. Yet some things can nevertheless be improved:
a) The number of entries of the current VLC is implicitly contained in
the run-length table and needn't be externally prescribed.
b) The maximum length of a code is just the length of the last code
(given that the lengths are ascending), so there is no point in setting
max_bits in the loop itself.
c) One can offload the actual calculation of the codes to
ff_init_vlc_from_lengths().
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Besides removing code duplication the method for determining the offset
of each VLC table in the VLC_TYPE buffer also has the advantage of not
wasting space for skipped AIC mode 1 VLCs.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
RealVideo 4.0 has a VLC that encodes two intra types per code; each
intra type is in the range 0..8 (inclusive) and up until now the VLC
used symbols in the range 0..80; one type was encoded as the remainder
when dividing the symbol by 9 whereas the other type was encoded as
symbol / 9. This is suboptimal; a better way would be to use the high
and low nibble to encode each symbol. But an even better way is to use
16bit symbols so that the two intra types can be directly written as
a 16bit value.
This commit implements this; in order to avoid huge tables the symbols
are stored as uint8_t with high and low nibbles encoding one type each;
they are only unpacked to uint16_t during initialization.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
After permuting the codes, symbols and lengths tables used to initialize
the VLC so that the codes are ordered from left to right in the Huffman
tree, the codes become redundant as they can be easily computed from the
lengths at runtime; in this case one has to use explicit symbol tables,
but all the symbols used here fit into an uint8_t, whereas some codes
needed uint16_t. This saves about 1.6KB.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
After permuting the codes, symbols and lengths tables used to initialize
the VLCs so that the codes are ordered from left to right in the Huffman
tree, the codes become redundant as they can be easily computed from the
lengths at runtime (or at compile time with --enable-hardcoded-tables);
in this case one has to use explicit symbol tables, but all the symbols
used here fit into an uint8_t, whereas some codes needed uint16_t.
Furthermore, the codes had holes because the range of the symbols was not
contiguous; these have also been removed.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
If both codes, lengths and symbols tables are ordered so that the codes
are sorted from left to right in the tree, the codes can be easily
derived from the lengths and therefore become redundant. This is
exploited in this commit to remove the codes tables for the mobiclip
decoder; notice that tables for the run-length VLC were already ordered
correctly.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Up until now, VLCs that were part of an array of VLCs were often not
initialized in a loop, but separately. The probable reason for this
was that these VLCs differed slightly in the parameters to be used for
them (i.e. the number of codes or the number of bits to be used
differs), so that one would have to provide these parameters e.g. via
arrays.
Yet these problems have actually largely been solved by now: The length
information is contained in a run-length encoded form that is the same
for all VLCs and both the number of codes as well as the number of bits
to use for each VLC can be easily derived from them.
There is just one problem to be solved: When the underlying tables have
a different number of elements, putting them into an array of arrays
would be wasteful; using an array of pointers to the arrays would
also be wasteful. Therefore this commit combines the tables into bigger
tables. (Given that all the length tables have the same layout this
applies only to the symbols tables.)
Finally, the array containing the offset of the VLC's buffer in the big
buffer has also been removed.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Several of the quantisation VLCs come in pairs and up until now the
number of bits used for each VLC was set to the same value for both VLCs
in such a pair even when one of the two required only a lower number.
This is a waste given that the get_vlc2() call is compatible with these
two VLCs using a different number of bits (it uses vlc->bits).
Given that the code lengths are descending it is easily possible to know
the length of the longest code for a given VLC: It is the length of the
first one. With this information one can easily use the least amount of
bits.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
After permuting both length, code as well as symbol tables so that
the codes are ordered from left to right in the tree, it became apparent
that the length of the codes decreases from left to right. Therefore one
can run-length encode the lengths to save space. This commit implements
this.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
By switching to ff_init_vlc_from_lengths() one can make a table of
codes of type uint8_t superfluous, saving space.
Other VLCs (those without dedicated symbols table and with codes of
type uint8_t) have been made to use ff_init_vlc_from_lengths(), too,
because it reduces codesize (ff_init_vlc_from_lengths() has two
parameters less than ff_init_vlc_sparse()) and because it allows to
use the offset parameter in future commits.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
By switching to ff_init_vlc_from_lengths() one can replace tables of
codes of type uint16_t with tables of symbols of type uint8_t, saving
space.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
By using ff_init_vlc_from_lengths(), we do not have to keep track of the
codes themselves, but can offload this to ff_init_vlc_from_lengths().
Furthermore, the old code presumed sizeof(int) == 4; this is no longer
so.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
By switching to ff_init_vlc_from_lengths() one can replace a table of
codes of type uint32_t with a table of symbols of type uint8_t saving
space. The old tables also had holes in it (because of the symbols) which
are now superfluous, saving ever more space.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
The VLC tables to be used for parsing RealVideo 1.0 DC coefficients are
weird: The luma table contains a block of 2^11 codes beginning with the
same prefix and length that all have the same symbol (i.e. value only
depends upon the prefix); the same goes for the chroma block (except
it's only 2^9 codes). Up until now, these entries (which generally could
be parsed like ordinary entries with subtables) have been treated
specially: They have been treated like open ends of the tree, so that
get_vlc2() returned a value < 0 upon encountering them; afterwards it
was checked whether the right prefix was used and if so, the appropriate
number of bytes was skipped.
But there is actually an easy albeit slightly hacky way to support them
directly without pointless subtables: Just modify the VLC table so that
all the entries sharing the right prefix have a length that equals the
length of the whole entry.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
These tables were huge (14 bits) because one needed 14 bits in order to
find out whether a code is valid and in the VLC table or a valid code that
required hacky workarounds due to RealVideo 1.0 using multiple codes
for the same symbol and the code predating the introduction of symbols
tables for VLCs.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
The RealVideo 1.0 decoder uses VLCs to parse DC coefficients. But the
values returned from get_vlc2() are not directly used; instead
-(val - 128) (which is in the range -127..128) is. This transformation
is unnecessary as it can effectively be done when initializing the VLC
by modifying the symbols table used. There is just one minor
complication: The chroma table is incomplete and in order to distinguish
an error from get_vlc2() (due to an invalid code) the ordinary return
range is modified to 0..255. This is possible because the only caller of
this function is (on success) only interested in the return value modulo
256.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
RealVideo 1.0 uses an insane way to encode DC coefficients: There are
several symbols that (for no good reason whatsoever) have multiple
encodings, leading to longer codes than necessary.
More specifically, the tree for the 256 luma symbols contains 255 codes
belonging to 255 different symbols on the left; going further right,
the tree consists of two blocks of 128 codes each of length 14 encoding
consecutive numbers (including two encodings for the symbol missing among
the 255 codes on the left); this is followed by two blocks of codes of
length 16 each containing 256 elements with consecutive symbols (i.e.
each of the blocks allows to encode all symbols). The rest of the tree
consists of 2^11 codes that all encode the same symbol.
The tree for the 256 chroma symbols is similar, but is missing the
blocks of length 256 and there are only 2^9 consecutive codes that
encode the same symbol; furthermore, the chroma tree is incomplete:
The right-most node has no right child.
All of this caused problems when parsing these codes; the reason is that
the code for this predates commit b613bacca9
which added support for explicit symbol tables and thereby removed the
requirement that different codes have different symbols. In order to
address this, the trees used for parsing were incomplete: They contained
the 255 codes on the left and one code for the remaining symbol. Whenever
a code not in these trees was encountered, it was dealt with in
special cases (one for each of the blocks mentioned above).
This commit reduces the number of special cases: Using a symbols table
allows to treat the blocks of consecutive symbols like ordinary codes;
only the blocks encoding a single symbol are still treated specially
(in order not to waste memory on tables for them).
In order to not increment the size of the tables used to initialize the
VLCs both the symbols as well as the lengths are now run-length encoded.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This can be achieved by switching to ff_init_vlc_from_lengths() which
allows to replace two uint16_t tables for codes with uint8_t tables for
the symbols by permuting the tables so that the codes are ordered from
left to right in the tree in which case they can be easily computed from
the lengths at runtime.
And after doing so, it became apparent that the tables for the symbols
are actually the same for luma and chroma, so that one can even omit one
of them.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Permuting the tables used to initialize the Cook VLCs so that the code
tables are ordered from left to right in the tree revealed that the
length of the codes are ascending from left to right. Therefore one can
run-length encode them to avoid the big length tables; this saves a bit
more than 1KB.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
