com.sun.media.imageioimpl.common

Class LZWStringTable

java.lang.Object

com.sun.media.imageioimpl.common.LZWStringTable

public class LZWStringTable
extends Object

General purpose LZW String Table. Extracted from GIFEncoder by Adam Doppelt Comments added by Robin Luiten expandCode added by Robin Luiten The strLen_ table to give quick access to the lenght of an expanded code for use by the expandCode method added by Robin.

Field Summary

Fields

Modifier and Type	Field and Description
private static short	HASH_FREE
private static short	HASHSIZE
private static short	HASHSTEP
private static int	MAXBITS
private static int	MAXSTR
private static short	NEXT_FIRST
(package private) short	numStrings_
private static int	RES_CODES codesize + Reserved Codes
(package private) byte[]	strChr_
(package private) short[]	strHsh_
(package private) int[]	strLen_ each entry corresponds to a code and contains the length of data that the code expands to when decoded.
(package private) short[]	strNxt_

Constructor Summary

Constructors

Constructor and Description
LZWStringTable() Constructor allocate memory for string store data

Method Summary

Modifier and Type	Method and Description
int	AddCharString(short index, byte b)
void	ClearTable(int codesize)
void	dump(PrintStream out)
int	expandCode(byte[] buf, int offset, short code, int skipHead) If expanded data doesnt fit into array only what will fit is written to buf and the return value indicates how much of the expanded code has been written to the buf.
short	FindCharString(short index, byte b)
static int	Hash(short index, byte lastbyte)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

RES_CODES

private static final int RES_CODES

codesize + Reserved Codes

See Also:

Constant Field Values

HASH_FREE

private static final short HASH_FREE

See Also:

Constant Field Values

NEXT_FIRST

private static final short NEXT_FIRST

See Also:

Constant Field Values

MAXBITS

private static final int MAXBITS

See Also:

Constant Field Values

MAXSTR

private static final int MAXSTR

See Also:

Constant Field Values

HASHSIZE

private static final short HASHSIZE

See Also:

Constant Field Values

HASHSTEP

private static final short HASHSTEP

See Also:

Constant Field Values

strChr_

byte[] strChr_

strNxt_

short[] strNxt_

strHsh_

short[] strHsh_

numStrings_

short numStrings_

strLen_

int[] strLen_

each entry corresponds to a code and contains the length of data that the code expands to when decoded.

Constructor Detail

LZWStringTable

public LZWStringTable()

Constructor allocate memory for string store data

Method Detail

AddCharString

public int AddCharString(short index,
                         byte b)

Parameters:

index - value of -1 indicates no predecessor [used in initialisation]

b - the byte [character] to add to the string store which follows the predecessor string specified the index.

Returns:

0xFFFF if no space in table left for addition of predecesor index and byte b. Else return the code allocated for combination index + b.

FindCharString

public short FindCharString(short index,
                            byte b)

Parameters:

index - index to prefix string

b - the character that follws the index prefix

Returns:

b if param index is HASH_FREE. Else return the code for this prefix and byte successor

ClearTable

public void ClearTable(int codesize)

Parameters:

codesize - the size of code to be preallocated for the string store.

Hash

public static int Hash(short index,
                       byte lastbyte)

expandCode

public int expandCode(byte[] buf,
                      int offset,
                      short code,
                      int skipHead)

If expanded data doesnt fit into array only what will fit is written to buf and the return value indicates how much of the expanded code has been written to the buf. The next call to expandCode() should be with the same code and have the skip parameter set the negated value of the previous return. Succesive negative return values should be negated and added together for next skip parameter value with same code.

Parameters:

buf - buffer to place expanded data into

offset - offset to place expanded data

code - the code to expand to the byte array it represents. PRECONDITION This code must allready be in the LZSS

skipHead - is the number of bytes at the start of the expanded code to be skipped before data is written to buf. It is possible that skipHead is equal to codeLen.

Returns:

the length of data expanded into buf. If the expanded code is longer than space left in buf then the value returned is a negative number which when negated is equal to the number of bytes that were used of the code being expanded. This negative value also indicates the buffer is full.

dump

public void dump(PrintStream out)