845dfa1986
This renames ec_dec_cdf() to ec_dec_icdf(), and changes the functionality to use an "inverse" CDF table, where icdf[i]=ft-cdf[i+1]. The first entry is omitted entirely. It also adds a corresonding ec_enc_icdf() to the encoder, which uses the same table. One could use ec_encode_bin() by converting the values in the tables back to normal CDF values, but the icdf[] table already has them in the form ec_encode_bin() wants to use them, so there's no reason to translate them and then translate them back. This is done primarily to allow SILK to use the range coder with 8-bit probability tables containing cumulative frequencies that span the full range 0...256. With an 8-bit table, the final 256 of a normal CDF becomes 0 in the "inverse" CDF. It's the 0 at the start of a normal CDF which would become 256, but this is the value we omit, as it already has to be special-cased in the encoder, and is not used at all in the decoder.
130 lines
5.5 KiB
C
130 lines
5.5 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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/*Encodes a symbol given an "inverse" CDF table.
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_s: The index of the symbol to encode.
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_icdf: The "inverse" CDF, such that symbol _s falls in the range
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[_s>0?ft-_icdf[_s-1]:0,ft-_icdf[_s]), where ft=1<<_ftb.
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The values must be monotonically non-increasing, and the last value
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must be 0.
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_ftb: The number of bits of precision in the cumulative distribution.*/
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void ec_enc_icdf(ec_enc *_this,int _s,const unsigned char *_icdf,unsigned _ftb);
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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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