74 lines
3 KiB
C
74 lines
3 KiB
C
#if !defined(_entdec_H)
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# define _entdec_H (1)
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# include "entcode.h"
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typedef struct ec_dec ec_dec;
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/*The entropy decoder.*/
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struct ec_dec{
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/*The buffer to decode.*/
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ec_byte_buffer *buf;
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/*The remainder of a buffered input symbol.*/
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int rem;
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/*The number of values in the current range.*/
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ec_uint32 rng;
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/*The difference between the input value and the lowest value in the current
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range.*/
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ec_uint32 dif;
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/*Normalization factor.*/
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ec_uint32 nrm;
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};
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/*Initializes the decoder.
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_buf: The input buffer to use.
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Return: 0 on success, or a negative value on error.*/
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void ec_dec_init(ec_dec *_this,ec_byte_buffer *_buf);
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/*Calculates the cumulative frequency for the next symbol.
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This can then be fed into the probability model to determine what that
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symbol is, and the additional frequency information required to advance to
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the next symbol.
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This function cannot be called more than once without a corresponding call to
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ec_dec_update(), or decoding will not proceed correctly.
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_ft: The total frequency of the symbols in the alphabet the next symbol was
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encoded with.
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Return: A cumulative frequency representing the encoded symbol.
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If the cumulative frequency of all the symbols before the one that
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was encoded was fl, and the cumulative frequency of all the symbols
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up to and including the one encoded is fh, then the returned value
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will fall in the range [fl,fh).*/
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unsigned ec_decode(ec_dec *_this,unsigned _ft);
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/*Advance the decoder past the next symbol using the frequency information the
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symbol was encoded with.
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Exactly one call to ec_decode() must have been made so that all necessary
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intermediate calculations are performed.
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_fl: The cumulative frequency of all symbols that come before the symbol
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decoded.
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_fh: The cumulative frequency of all symbols up to and including the symbol
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Together with _fl, this defines the range [_fl,_fh) in which the value
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returned above must fall.
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_ft: The total frequency of the symbols in the alphabet the symbol decoded
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was encoded in.
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This must be the same as passed to the preceding call to ec_decode().*/
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void ec_dec_update(ec_dec *_this,unsigned _fl,unsigned _fh,
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unsigned _ft);
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/*Extracts a sequence of raw bits from the stream.
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The bits must have been encoded with ec_enc_bits().
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No call to ec_dec_update() is necessary after this call.
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_ftb: The number of bits to extract.
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This must be at least one, and no more than 32.
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Return: The decoded bits.*/
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ec_uint32 ec_dec_bits(ec_dec *_this,int _ftb);
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/*Extracts a raw unsigned integer with a non-power-of-2 range from the stream.
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The bits must have been encoded with ec_enc_uint().
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No call to ec_dec_update() is necessary after this call.
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_ft: The number of integers that can be decoded (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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Return: The decoded bits.*/
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ec_uint32 ec_dec_uint(ec_dec *_this,ec_uint32 _ft);
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#endif
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