ref: 17cab431dba2ecb10d3d5d70763b185d095e9cc8
dir: /libcelt/entdec.h/
/* Copyright (c) 2001-2008 Timothy B. Terriberry
Copyright (c) 2008-2009 Xiph.Org Foundation */
/*
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
- Neither the name of the Xiph.org Foundation nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#if !defined(_entdec_H)
# define _entdec_H (1)
# include <limits.h>
# include "entcode.h"
typedef struct ec_dec ec_dec;
/*The entropy decoder.*/
struct ec_dec{
/*The buffer to decode.*/
ec_byte_buffer *buf;
/*The remainder of a buffered input symbol.*/
int rem;
/*The number of values in the current range.*/
ec_uint32 rng;
/*The difference between the top of the current range and the input value,
minus one.*/
ec_uint32 dif;
/*Normalization factor.*/
ec_uint32 nrm;
/*Bits that were written at the end.*/
ec_window end_window;
/*Number of valid bits in end_window.*/
int nend_bits;
/*The total number of whole bits read.*/
int nbits_total;
/*Nonzero if an error occurred.*/
int error;
};
/*Initializes the decoder.
_buf: The input buffer to use.
Return: 0 on success, or a negative value on error.*/
void ec_dec_init(ec_dec *_this,ec_byte_buffer *_buf);
/*Calculates the cumulative frequency for the next symbol.
This can then be fed into the probability model to determine what that
symbol is, and the additional frequency information required to advance to
the next symbol.
This function cannot be called more than once without a corresponding call to
ec_dec_update(), or decoding will not proceed correctly.
_ft: The total frequency of the symbols in the alphabet the next symbol was
encoded with.
Return: A cumulative frequency representing the encoded symbol.
If the cumulative frequency of all the symbols before the one that
was encoded was fl, and the cumulative frequency of all the symbols
up to and including the one encoded is fh, then the returned value
will fall in the range [fl,fh).*/
unsigned ec_decode(ec_dec *_this,unsigned _ft);
unsigned ec_decode_bin(ec_dec *_this,unsigned _bits);
/*Advance the decoder past the next symbol using the frequency information the
symbol was encoded with.
Exactly one call to ec_decode() must have been made so that all necessary
intermediate calculations are performed.
_fl: The cumulative frequency of all symbols that come before the symbol
decoded.
_fh: The cumulative frequency of all symbols up to and including the symbol
decoded.
Together with _fl, this defines the range [_fl,_fh) in which the value
returned above must fall.
_ft: The total frequency of the symbols in the alphabet the symbol decoded
was encoded in.
This must be the same as passed to the preceding call to ec_decode().*/
void ec_dec_update(ec_dec *_this,unsigned _fl,unsigned _fh,
unsigned _ft);
/*Extracts a sequence of raw bits from the stream.
The bits must have been encoded with ec_enc_bits().
No call to ec_dec_update() is necessary after this call.
_ftb: The number of bits to extract.
This must be between 0 and 25, inclusive.
Return: The decoded bits.*/
ec_uint32 ec_dec_bits(ec_dec *_this,unsigned _ftb);
/*Extracts a raw unsigned integer with a non-power-of-2 range from the stream.
The bits must have been encoded with ec_enc_uint().
No call to ec_dec_update() is necessary after this call.
_ft: The number of integers that can be decoded (one more than the max).
This must be at least one, and no more than 2**32-1.
Return: The decoded bits.*/
ec_uint32 ec_dec_uint(ec_dec *_this,ec_uint32 _ft);
/*Decodes a symbol given an "inverse" CDF table.
No call to ec_dec_update() is necessary after this call.
_icdf: The "inverse" CDF, such that symbol s falls in the range
[s>0?ft-_icdf[s-1]:0,ft-_icdf[s]), where ft=1<<_ftb.
The values must be monotonically non-increasing, and the last value
must be 0.
_ftb: The number of bits of precision in the cumulative distribution.
Return: The decoded symbol s.*/
int ec_dec_icdf(ec_dec *_this,const unsigned char *_icdf,unsigned _ftb);
/* Decode a bit that has a _prob/65536 probability of being a one */
int ec_dec_bit_prob(ec_dec *_this,unsigned _prob);
/* Decode a bit that has a 1/(1<<_logp) probability of being a one */
int ec_dec_bit_logp(ec_dec *_this,unsigned _logp);
/*Returns the number of bits "used" by the encoded symbols so far.
This same number can be computed by the encoder, and is suitable for making
coding decisions.
_b: The number of extra bits of precision to include.
At most 16 will be accurate.
Return: The number of bits scaled by 2**_b.
This will always be slightly larger than the exact value (e.g., all
rounding error is in the positive direction).*/
ec_uint32 ec_dec_tell(ec_dec *_this,int _b);
/*Return: A nonzero value if any error has been detected during decoding.*/
int ec_dec_get_error(ec_dec *_this);
#endif