30df6cf3f8
This simplifies a good bit of the error handling, and should make it
impossible to overrun the buffer in the encoder or decoder, while
still allowing tell() to operate correctly after a bust.
The encoder now tries to keep the range coder data intact after a
bust instead of corrupting it with extra bits data, though this is
not a guarantee (too many extra bits may have already been flushed).
It also now correctly reports errors when the bust occurs merging the
last byte of range coder and extra bits.
A number of abstraction barrier violations were cleaned up, as well.
This patch also includes a number of minor performance improvements:
ec_{enc|dec}_bits() in particular should be much faster.
Finally, tf_select was changed to be coded with the range coder
rather than extra bits, so that it is at the front of the packet
(for unequal error protection robustness).
121 lines
5 KiB
C
121 lines
5 KiB
C
/* Copyright (c) 2001-2008 Timothy B. Terriberry
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Copyright (c) 2008-2009 Xiph.Org Foundation */
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/*
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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- Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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- Neither the name of the Xiph.org Foundation nor the names of its
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contributors may be used to endorse or promote products derived from
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this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR
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CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#if !defined(_entenc_H)
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# define _entenc_H (1)
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# include <stddef.h>
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# include "entcode.h"
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typedef struct ec_enc ec_enc;
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/*The entropy encoder.*/
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struct ec_enc{
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/*Buffered output.*/
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ec_byte_buffer *buf;
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/*A buffered output symbol, awaiting carry propagation.*/
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int rem;
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/*Number of extra carry propagating symbols.*/
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size_t ext;
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/*The number of values in the current range.*/
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ec_uint32 rng;
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/*The low end of the current range (inclusive).*/
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ec_uint32 low;
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/*Bits that will be written at the end.*/
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ec_window end_window;
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/*Number of valid bits in end_window.*/
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int nend_bits;
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/*The total number of whole bits written.*/
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int nbits_total;
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/*Nonzero if an error occurred.*/
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int error;
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};
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/*Initializes the encoder.
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_buf: The buffer to store output bytes in.
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This must have already been initialized for writing and reset.*/
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void ec_enc_init(ec_enc *_this,ec_byte_buffer *_buf);
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/*Encodes a symbol given its frequency information.
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The frequency information must be discernable by the decoder, assuming it
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has read only the previous symbols from the stream.
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It is allowable to change the frequency information, or even the entire
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source alphabet, so long as the decoder can tell from the context of the
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previously encoded information that it is supposed to do so as well.
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_fl: The cumulative frequency of all symbols that come before the one to be
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encoded.
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_fh: The cumulative frequency of all symbols up to and including the one to
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be encoded.
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Together with _fl, this defines the range [_fl,_fh) in which the
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decoded value will fall.
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_ft: The sum of the frequencies of all the symbols*/
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void ec_encode(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _ft);
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void ec_encode_bin(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _bits);
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/*Encodes a sequence of raw bits in the stream.
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_fl: The bits to encode.
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_ftb: The number of bits to encode.
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This must be between 0 and 25, inclusive.*/
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void ec_enc_bits(ec_enc *_this,ec_uint32 _fl,unsigned _ftb);
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/*Encodes a raw unsigned integer in the stream.
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_fl: The integer to encode.
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_ft: The number of integers that can be encoded (one more than the max).
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This must be at least one, and no more than 2**32-1.*/
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void ec_enc_uint(ec_enc *_this,ec_uint32 _fl,ec_uint32 _ft);
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/* Encode a bit that has a _prob/65536 probability of being a one */
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void ec_enc_bit_prob(ec_enc *_this,int val,unsigned _prob);
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/* Encode a bit that has a 1/(1<<_logp) probability of being a one */
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void ec_enc_bit_logp(ec_enc *_this,int _val,unsigned _logp);
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/*Returns the number of bits "used" by the encoded symbols so far.
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This same number can be computed by the decoder, and is suitable for making
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coding decisions.
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_b: The number of extra bits of precision to include.
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At most 16 will be accurate.
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Return: The number of bits scaled by 2**_b.
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This will always be slightly larger than the exact value (e.g., all
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rounding error is in the positive direction).*/
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ec_uint32 ec_enc_tell(ec_enc *_this,int _b);
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/*Indicates that there are no more symbols to encode.
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All reamining output bytes are flushed to the output buffer.
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ec_enc_init() must be called before the encoder can be used again.*/
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void ec_enc_done(ec_enc *_this);
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/*Returns a nonzero value if any error has been detected during encoding*/
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int ec_enc_get_error(ec_enc *_this);
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#endif
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