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

Constituent: encdec     Tag: sun-gcc

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APE.h File Reference

Arithmetic Word Encoder interface file. More...

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Data Structures
union	_APE_cv
	Defines the limits of the condition value as union between the field definition two 32-bit integers and an interpretted 64-bit number. More...
struct	_APE_cv_ui
	Defines the limits of the condition value as two 32-bit integers. More...
struct	_APE_etx
	Encoding context. More...
Typedefs
typedef _APE_cv_ui	APE_cv_ui
	Typedef for APE_cv_ui.
typedef _APE_cv	APE_cv
	Typedef for APE_cv.
typedef _APE_etx	APE_etx
	Typedef for struct _APE_etx.
Functions
unsigned int	APE_bcompress (unsigned char *out, unsigned int boff, unsigned char *max, const unsigned int *table, const unsigned char *in, int cnt, int *unencoded)
	Convenience routine to compress a byte stream.
int	APE_reset (APE_etx *etx, unsigned char *out, unsigned int boff, const unsigned char *max)
	Resets the output context.
int	APE_start (APE_etx *etx, unsigned char *out, unsigned int boff, const unsigned char *max)
	Initializes the encoding context.
int	APE_encode (APE_etx *etx, const unsigned int *table, unsigned int sym)
	Encodes one symbol.
int	APE_bencode (APE_etx *etx, const unsigned int *table, const unsigned char *syms, int nsyms)
	Encodes an array of unsigned char symbols.
int	APE_sencode (APE_etx *etx, const unsigned int *table, const unsigned short *syms, int nsyms)
	Encodes an array of unsigned char symbols.
int	APE_finish (APE_etx *etx)
	Finishes the encoding by flushing out any currently buffered bits.

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Detailed Description

Arithmetic Word Encoder interface file.

Author:

JJRussell - russell@slac.stanford.edu

    CVS $Id: APE.h,v 1.1.1.1 2005/09/23 06:41:07 russell Exp $

Interface specification for routines to encode symbols using an arithmetic encoding technique. The encoding tables are 32-bits wide. This allows probabilities to (in principle) hold a range of 1/2**32. Contrast this with the ABx routines which only use a range of 1/2**16.

Do not confuse the width of the symbol being encoded with the width of the probability tables. The width of the symbol being encoded is not a fundamental property of these routines. That is, these routines can be used to encode all different symbol widths. All that the user needs to do is provide an appropriately sized probability tables. In essence, the symbol is used to index the probability table, giving the probability of that symbol.

The choice of using the ABx or AWx routines is driven by the range of the relative probabilities. If the range is large, then the AWx routines should be used. If the range is small, then the ABx routines should be used. In general the ABx routines have better runtime performance and the AWx routines come closer to achieving the theorical maximum compression.

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Typedef Documentation

APE_etx

Typedef for struct _APE_etx. While this is defined in the public interface, this structure should be treated like a C++ private member. All manipulation of this structure should be through the APE routines.

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Function Documentation

unsigned int APE_bcompress (  unsigned char *  out, unsigned int  boff, unsigned char *  max, const unsigned int *  table, const unsigned char *  in, int  cnt, int *  unencoded )

Convenience routine to compress a byte stream. Returns: The number of bits needed to encoded the byte stream. If negative the all the symbols could not be encoded and unencoded should be checked for the count of those symbols not encoded. Parameters: out  The output buffer boff  The current bit offset max  The maximum output address (actually 1 byte past it) table  The encoding table in  The input buffer of symbols. cnt  The number of input symbols. unencoded  The number of input symbols left to encode. If successful this will be 0. This is a convenience routine, combining APE_start(), APE_encode() and APE_finish(). It can be used iff the same table is used to encode all the symbols.

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int APE_bencode (  APE_etx *  etx, const unsigned int *  table, const unsigned char *  syms, int  nsyms )

Encodes an array of unsigned char symbols. Returns: Number of symbols remaining to be encoded. If this is 0, all symbols where encoded. Parameters: etx  The encoding context table  The encoding table syms  The array of symbols to encode nsyms  The number of symbols

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int APE_encode (  APE_etx *  etx, const unsigned int *  table, unsigned int  sym )

Encodes one symbol. Returns: Number of symbols remaining to be encoded. If this is 0, the symbol was successfully encoded. Parameters: etx  The encoding context table  The encoding table sym  The symbol to encode

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int APE_finish (  APE_etx *  etx  )

Finishes the encoding by flushing out any currently buffered bits. Return values: If  > 0, the number of encoded bits. If < 0, the number of bits needed to encode the final piece Parameters: etx  The encoding context At the end of the encoding, there is some context that needs flushing. This flushing may contribute more bits to the output stream. If there are not enough bits to hold this context, the number of extra bits needed to flush the context are returned as a negative number. In this case, the user should write all the currently committed data and then reset the output buffer. The array to write out is from etx->beg + etx->bbeg (the beginning output address + beginning bit number to ext->out (the current output address). Once written, the user should call APE_reset to reset the output buffer. If there is enough room, the number of encoded bits is returned as a positive number.

int APE_reset (  APE_etx *  etx, unsigned char *  out, unsigned int  boff, const unsigned char *  max )

Resets the output context. Return values: 0,If  successful -1,If  failed to provide at least 1 byte of memory. Parameters: etx  The encoding context to reset out  The output buffer. boff  The bit offset into the output buffer. max  The maximum output address (actually 1 byte past it) Note that since the AWx routines are bit encoders/decoders, one needs to specify the offsets into the buffers as bit offsets. In general, at least one byte of memory needs to be provided. There is no check for this failure

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int APE_sencode (  APE_etx *  etx, const unsigned int *  table, const unsigned short *  syms, int  nsyms )

Encodes an array of unsigned char symbols. Returns: Number of symbols remaining to be encoded. If this is 0, all symbols where encoded. Parameters: etx  The encoding context table  The encoding table syms  The array of symbols to encode nsyms  The number of symbols

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int APE_start (  APE_etx *  etx, unsigned char *  out, unsigned int  boff, const unsigned char *  max )

Initializes the encoding context. Return values: 0,Currently,always  0. This may expand to a status code if necessary Parameters: etx  The encoding context to initialize out  The output buffer boff  The bit offset into the output buffer max  The maximum output address (actually 1 byte past it) Note that since the AWx routines are bit encoders/decoders, one needs to specify the offsets into the buffers as bit offsets.

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