HDE.c File Reference

Implementation of the routines to encodes a distribution of symbols using a Huffman encoding technique. Routines are available to encode both the distribution itself and the resulting Huffman table. More...

#include "LDT/HDE.h"
#include "LDT/HUFF.h"
#include "LDT/BFP.h"
#include "ffs.h"
#include "dprintf.h"
#include <math.h>

Include dependency graph for HDE.c:


Data Structures
struct	_HistLimits
	Min and Max indices of a histogram. More...
Defines
#define	NULL ((void *)(0))
Typedefs
typedef _HistLimits	HistLimits
	Typedef for struct _HistLimits.
Functions
static __inline HistLimits	hist_limits_find (const unsigned short int *hist, int cnt)
static __inline int	hist_copy (unsigned int dst, const unsigned short int src, int min, int max)
	Copies the core of the histogram (i.e. from the first non-zero element to the last non-zero element.
static __inline unsigned int	huff_table_encode (unsigned int buf, unsigned int pos, const HUFF_code codes, const unsigned int *freq, int nentries, int nbits_min, int min)
	Encodes the Huffman encoding table.
static __inline unsigned int	huff_symbols_encode (unsigned int buf, unsigned int pos, const HUFF_code codes, const short int *symbols, int nsymbols)
	Encodes the pedestal subtracted ADC values using the specified Huffman codes.
	_declare (static double calc_nbits(const int *f, int cnt, int tot))
unsigned int	HDE_encodeSS (unsigned int buf, unsigned int pos, const unsigned short int hist, int nbins, const short int *symbols, int nsymbols)
	Encodes the specified symbols symbols using the specified histogram of frequencies. Both the symbols and the histogram are presented as 16-bit values.
double	calc_nbits (const int *f, int cnt, int tot)
	Calculates the number of bits need to encode a sample with the specified frequency distribution.

Detailed Description

Implementation of the routines to encodes a distribution of symbols using a Huffman encoding technique. Routines are available to encode both the distribution itself and the resulting Huffman table.

Author:: JJRussell - russell@slac.stanford.edu

   CVS $Id: HDE.c,v 1.2 2006/09/13 17:58:41 russell Exp $

Typedef Documentation

static __inline HistLimits

Typedef for struct _HistLimits.
cal_hist_limits_find (const unsigned short int *hist, int cnt)

Parameters:

hist The target histogram

cnt The total number of entries in the histogram

Function Documentation

static double calc_nbits ( const int * f,

int cnt,

int tot

)

Calculates the number of bits need to encode a sample with the specified frequency distribution.

Parameters:

f The frequency distribution

cnt The count of entries in the frequency distribution

tot The total number of entries in the frequency distribution

This is based on the following formula
nbits = - TOT * SUM [ f[i] / TOT * ln (f[i] / TOT) ] = - TOT/TOT * SUM [ f[i] * (ln (f[i]) - ln (TOT)) ] = - SUM [ f[i] * ln (f[i] ] + SUM [ f[i] * ln (TOT) ] = - SUM [ f[i] * ln (f[i] ] + TOT * ln (TOT) ]

unsigned int HDE_encodeSS ( unsigned int * buf,

unsigned int pos,

const unsigned short int * hist,

int nbins,

const short int * symbols,

int nsymbols

)

Encodes the specified symbols symbols using the specified histogram of frequencies. Both the symbols and the histogram are presented as 16-bit values.

Returns:
The updated bit write position

Parameters:

buf The output buffer address

pos The current write bit offset

hist The frequency histogram

nbins The number of bins in the histogram

symbols The array of symbols

nsymbols The number of symbols

static __inline int hist_copy ( unsigned int * dst,

const unsigned short int * src,

int min,

int max

) [static]

Copies the core of the histogram (i.e. from the first non-zero element to the last non-zero element.

Parameters:

dst The destination histogram

src The source histogram

min The first non-zero histogram bin

max The last non-zero histogram bin

This routine exists solely because the HUFF build routines only take an integer (not a short integer) frequency distribution.

static __inline unsigned int huff_symbols_encode ( unsigned int * buf,

unsigned int pos,

const HUFF_code * codes,

const short int * symbols,

int nsymbols

) [static]

Encodes the pedestal subtracted ADC values using the specified Huffman codes.

Returns:
The updated write bit position

Parameters:

buf The output buffer

pos The position of the next bit to fill

codes The Huffman codes

symbols The symbols to encode

nsymbols The number of symbols to encode

static __inline unsigned int huff_table_encode ( unsigned int * buf,

unsigned int pos,

const HUFF_code * codes,

const unsigned int * freq,

int cnt,

int nbits_min,

int min

) [static]

Encodes the Huffman encoding table.

Returns:
The updated write bit position

Parameters:

buf The output buffer

pos The position of the next bit to fill

codes The Huffman codes

freq The frequency distribution. This is used to determine valid members.

cnt The count of codes

nbits_min The number bits to use in encoding the minimum, min If 0, the minimum offset will not be encoded If -1, the number of bits will be computed from min itself and stored as a 5-bit number

min The offset of the table. This value should be added onto the decoded symbol

The encoding is

nbits_min: 5, number of bits used to encode the minimum symbol value (fixed 5 bits)
min: nbits_min, the minumum symbol value
nbits_rl : 5, number of bits needed to encode the maximum run length, if 0, then this is a 0 entropy distribution with the only value of 'min'
rl[0] : Run length of the run of symbols
rl[1] : Run length till the next block of symbols, if 0, then finished. Note that the finish must always be on an odd run length index.
nbits_cl : 5, number of bits needed to hold the maximum code length
cl[0] : nbits_cl, the code length of the first symbol
cl[1] : nbits_cl, the code length of the second symbol
.
.
cl[n] : nbits_cl, the code length of the last symbol, the number of symbols is derived from the run length decoding

Generated on Thu Sep 14 09:17:33 2006 by

1.4.4

HDE.c File Reference

Data Structures

Defines

Typedefs

Functions

Detailed Description

Typedef Documentation

Function Documentation