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GLAST/LAT > DAQ and FSW > FSW > Doxygen Index > LDT / V0-0-0

Constituent: encdec     Tag: rad750

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APD.c File Reference

Arithmetic Byte Decoder, implementation file. More...

#include "APC.h"
#include "LDT/APD.h"

Include dependency graph for APD.c:

Functions
void	APD_start (APD_dtx *dtx, const unsigned char *in, unsigned int boff)
	Begins a decoding session.
int	APD_bdecompress (unsigned char *out, int cnt, const unsigned char *in, unsigned int boff, const unsigned int *table)
	Convenience routine to decode a bit stream using the specified table.
unsigned int	APD_decode (APD_dtx *dtx, const unsigned int *table)
	Decodes the next symbol.
int	APD_finish (APD_dtx *dtx)
	Finishes the decoding, cleaning up any inprogress context.

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Detailed Description

Arithmetic Byte Decoder, implementation file.

Author:

JJRussell - russell@slac.stanford.edu

Implementation of the routines to decode bit streams using an arithmetic probability encoding technique. To successfully decode an input stream, the encoder and decoder must agree on the modeling table. This modeling table is generally constructed from a frequency distribution derived from the actual data to be encoded or from a distribution thought to be highly representative (in a statisical sense) of the distribution to be encoded. This frequency distribution must then be transformed into the encoding/decoding modeling table.

To achieve performance goals, particularly on the encoding side, these routines must be used with a model builder that forces a particular normalization of the cumulative probability. While such tables may be constructed in a variety of ways, APM_build is an example of such a routine and is anticipated to be the model table builder

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Function Documentation

int APD_bdecompress (  unsigned char *  out, int  cnt, const unsigned char *  in, unsigned int  boff, const unsigned int *  table )

Convenience routine to decode a bit stream using the specified table. Returns: The number of decoded bits Parameters: out  The output buffer cnt  The number of bytes in the output buffer in  The input buffer boff  The bit offset to start at in the input buffer table  The decoding table This is a convenience routine, combining APD_start, APD_decode and APD_finish. This routine can only be used if the decoding table is the same for all symbols in the input stream.

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unsigned int APD_decode (  APD_dtx *  dtx, const unsigned int *  table )

Decodes the next symbol. Returns: The decoded symbol Parameters: dtx  The decoding context table  The table to use in the decoding

int APD_finish (  APD_dtx *  dtx  )

Finishes the decoding, cleaning up any inprogress context. Returns: The number of bits decoded

void APD_start (  APD_dtx *  dtx, const unsigned char *  in, unsigned int  boff )

Begins a decoding session. Parameters: dtx  The decoding context to be initialized in  The input bit stream boff  The bit offset into the input bit stream

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