CEZCompressor Class Reference

#include <ezcompressor.h>

Link against: ezlib.lib

class CEZCompressor : public CEZZStream

Inherits from

CEZCompressor
- CEZZStream

Public Member Enumerations
enum	anonymous { EDefaultCompression, ENoCompression, EBestSpeed, EBestCompression }
enum	anonymous { EMaxWBits }
enum	anonymous { EDefMemLevel }
enum	anonymous { EDeflateInitlialiserError, EDeflateTerminated }
enum	TStrategy { EDefaultStrategy, EFiltered, EHuffmanOnly }

Public Member Functions
	~CEZCompressor()
IMPORT_C void	CompressL(TDes8 &, const TDesC8 &, TInt)
IMPORT_C TBool	DeflateL()
IMPORT_C CEZCompressor *	NewL(MEZBufferManager &, TInt, TInt, TInt, TStrategy)
IMPORT_C CEZCompressor *	NewL(MEZBufferManager &, const TDesC8 &, TInt, TInt, TInt, TStrategy)
IMPORT_C CEZCompressor *	NewLC(MEZBufferManager &, TInt, TInt, TInt, TStrategy)
IMPORT_C CEZCompressor *	NewLC(MEZBufferManager &, const TDesC8 &, TInt, TInt, TInt, TStrategy)
IMPORT_C void	ResetL(MEZBufferManager &)

Inherited Attributes
	CEZZStream::iOutputBufferLength
	CEZZStream::iOutputPointer
	CEZZStream::iStream

Inherited Enumerations
	CEZZStream:@26

Inherited Functions
	CBase::CBase()
	CBase::Delete(CBase *)
	CBase::Extension_(TUint,TAny &,TAny )
	CBase::operator new(TUint)
	CBase::operator new(TUint,TAny *)
	CBase::operator new(TUint,TLeave)
	CBase::operator new(TUint,TLeave,TUint)
	CBase::operator new(TUint,TUint)
	CBase::~CBase()
	CEZZStream::Adler32()const
	CEZZStream::AvailIn()const
	CEZZStream::AvailOut()const
	CEZZStream::CEZZStream()
	CEZZStream::OutputDescriptor()const
	CEZZStream::Progress(TInt)const
	CEZZStream::SetInput(const TDesC8 &)
	CEZZStream::SetOutput(TDes8 &)
	CEZZStream::TotalIn()const
	CEZZStream::TotalOut()const

Detailed Description

The CEZCompressor class provides in-memory compression functions, including integrity checks of the uncompressed data. This version of the library supports only one compression method (deflation). Compression can be done in a single step (using CompressL()) if the buffers are large enough (for example if an input file is mmap'ed), or can be done by repeated calls of the DeflateL() function. The source data is compressed to the target buffer (both source and target contained within the buffer manager argument), and various other arguments distinguish the different compression settings.

Note: In this version of the library a windowBits value of 8 is unsupported due to a problem with the window size being set to 256 bytes. Although a value of 8 will be accepted by the CEZCompressor constructors, as it is being changed internally by Zlib from 8 to 9, it will not be possible to use the same value for decompression. This is because the Zlib functions called by the CEZDecompressor constructors do not make the same change internally and as a result a KEZlibErrData is returned when calling InflateL(). It is therefore advised that for this version of the library windowBits of 9 is used in place of 8.

Member Enumeration Documentation

Enum anonymous

Compression levels

Enumerator	Value	Description
EDefaultCompression	Z_DEFAULT_COMPRESSION
ENoCompression	Z_NO_COMPRESSION
EBestSpeed	Z_BEST_SPEED
EBestCompression	Z_BEST_COMPRESSION

Enum anonymous

Window Bits - the base two logarithm of the window size (the size of the history buffer)

Enumerator	Value	Description
EMaxWBits	MAX_WBITS

Enum anonymous

Memory level - specifies how much memory should be allocated for the internal compression state

Enumerator	Value	Description
EDefMemLevel	MAX_MEM_LEVEL

Enum anonymous

Compression panic values

Enumerator	Value	Description
EDeflateInitlialiserError	EUnexpected + 1
EDeflateTerminated

Enum TStrategy

Compression strategy - used to tune the compression algorithm

Enumerator	Value	Description
EDefaultStrategy	Z_DEFAULT_STRATEGY	Use for normal data
EFiltered	Z_FILTERED	Use for data produced by a filter (or predictor)
EHuffmanOnly	Z_HUFFMAN_ONLY	Force Huffman encoding only (no string match)

Constructor & Destructor Documentation

~CEZCompressor ( )

~CEZCompressor

(

)

Member Function Documentation

CompressL ( TDes8 &, const TDesC8 &, TInt )

IMPORT_C void	CompressL	(	TDes8 &	aDestination,
			const TDesC8 &	aSource,
			TInt	aLevel = EDefaultCompression
		)	[static]

Compresses the data in the given buffer

leave: KEZLibErrBuf There is a problem with the buffer

leave: KEZLIbErrStream There is a problem with the stream

leave: ... Any of the system wide error codes

Parameter	Description
aDestination	the target buffer for the compressed data
aSource	the buffer containing the data to be compressed
aLevel	the level of compression

DeflateL ( )

IMPORT_C TBool

DeflateL

(

)

Compress the data to the buffer in stages, return value indicates if the compression has finalised or if further calls are necessary

leave: KEZlibErrStream There is a problem with the stream

leave: KEZlibErrBuf There is a problem with the buffer

leave: KEZlibErrUnexpected Unexpected programming error

leave: ... Any of the System wide error codes

Returns: ETrue if the function must be called again, EFalse if compression is finalised

NewL ( MEZBufferManager &, TInt, TInt, TInt, TStrategy )

IMPORT_C CEZCompressor *	NewL	(	MEZBufferManager &	aInit,
			TInt	aLevel = EDefaultCompression,
			TInt	aWindowBits = EMaxWBits,
			TInt	aMemLevel = EDefMemLevel,
			TStrategy	aStrategy = EDefaultStrategy
		)	[static]

Creates a new CEZCompressor object

See also: TStrategy

Parameter	Description
aInit	buffer manager to handle both input and output buffers
aLevel	compression levels
aWindowBits	the base two logarithm of the window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. Larger values of this parameter result in better compression at the expense of memory usage.
aMemLevel	specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed.
aStrategy	compression strategy - used to tune the compression algorithm. The strategy parameter only affects the compression ratio but not the correctness of the compressed output even if it is not set appropriately

Returns: the new CEZCompressor object

NewL ( MEZBufferManager &, const TDesC8 &, TInt, TInt, TInt, TStrategy )

IMPORT_C CEZCompressor *	NewL	(	MEZBufferManager &	aInit,
			const TDesC8 &	aDictionary,
			TInt	aLevel = EDefaultCompression,
			TInt	aWindowBits = EMaxWBits,
			TInt	aMemLevel = EDefMemLevel,
			TStrategy	aStrategy = EDefaultStrategy
		)	[static]

Overload of CEZCompressor constructor takes aDictionary argument

See also: TStrategy

Parameter	Description
aInit	buffer manager to handle both input and output buffers
aDictionary	used to initialize the compression dictionary from the given byte sequence without producing any compressed output. The compressor and decompressor must use exactly the same dictionary. The dictionary should consist of strings (byte sequences) that are likely to be encountered later in the data to be compressed, with the most commonly used strings preferably put towards the end of the dictionary. Using a dictionary is most useful when the data to be compressed is short and can be predicted with good accuracy; the data can then be compressed better than with the default empty dictionary.
aLevel	compression level
aWindowBits	the base two logarithm of the window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. Larger values of this parameter result in better compression at the expense of memory usage.
aMemLevel	specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed.
aStrategy	compression strategy - used to tune the compression algorithm. The strategy parameter only affects the compression ratio but not the correctness of the compressed output even if it is not set appropriately

Returns: the new CEZCompressor object

NewLC ( MEZBufferManager &, TInt, TInt, TInt, TStrategy )

IMPORT_C CEZCompressor *	NewLC	(	MEZBufferManager &	aInit,
			TInt	aLevel = EDefaultCompression,
			TInt	aWindowBits = EMaxWBits,
			TInt	aMemLevel = EDefMemLevel,
			TStrategy	aStrategy = EDefaultStrategy
		)	[static]

Creates a new CEZCompressor object and leaves it on the CleanupStack

See also: TStrategy

Parameter	Description
aInit	buffer manager to handle both input and output buffers
aLevel	compression levels
aWindowBits	the base two logarithm of the window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. Larger values of this parameter result in better compression at the expense of memory usage.
aMemLevel	specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed.
aStrategy	compression strategy - used to tune the compression algorithm. The strategy parameter only affects the compression ratio but not the correctness of the compressed output even if it is not set appropriately

Returns: the new CEZCompressor object (on the CleanupStack)

NewLC ( MEZBufferManager &, const TDesC8 &, TInt, TInt, TInt, TStrategy )

IMPORT_C CEZCompressor *	NewLC	(	MEZBufferManager &	aInit,
			const TDesC8 &	aDictionary,
			TInt	aLevel = EDefaultCompression,
			TInt	aWindowBits = EMaxWBits,
			TInt	aMemLevel = EDefMemLevel,
			TStrategy	aStrategy = EDefaultStrategy
		)	[static]

Overload of CEZCompressor constructor takes aDictionary argument

See also: TStrategy

Parameter	Description
aInit	buffer manager to handle both input and output buffers
aDictionary	used to initialize the compression dictionary from the given byte sequence without producing any compressed output. The compressor and decompressor must use exactly the same dictionary. The dictionary should consist of strings (byte sequences) that are likely to be encountered later in the data to be compressed, with the most commonly used strings preferably put towards the end of the dictionary. Using a dictionary is most useful when the data to be compressed is short and can be predicted with good accuracy; the data can then be compressed better than with the default empty dictionary.
aLevel	compression level
aWindowBits	the base two logarithm of the window size (the size of the history buffer). It should be in the range 8..15 for this version of the library. Larger values of this parameter result in better compression at the expense of memory usage.
aMemLevel	specifies how much memory should be allocated for the internal compression state. memLevel=1 uses minimum memory but is slow and reduces compression ratio; memLevel=9 uses maximum memory for optimal speed.
aStrategy	compression strategy - used to tune the compression algorithm. The strategy parameter only affects the compression ratio but not the correctness of the compressed output even if it is not set appropriately

Returns: the new CEZCompressor object (on the CleanupStack)

ResetL ( MEZBufferManager & )

IMPORT_C void

ResetL

(

MEZBufferManager &

aInit

)

Resets the current compression operation, with the new buffer manager

leave: ... Any of the system wide error codes

Parameter	Description
aInit	new buffer manager to handle the new input and output buffers