zlib-0.6.1.2: Compression and decompression in the gzip and zlib formats

Copyright(c) 2006-2014 Duncan Coutts
LicenseBSD-style
Maintainerduncan@community.haskell.org
Safe HaskellSafe
LanguageHaskell2010

Codec.Compression.Zlib.Raw

Contents

Description

Compression and decompression of data streams in the raw deflate format.

The format is described in detail in RFC #1951: http://www.ietf.org/rfc/rfc1951.txt

See also the zlib home page: http://zlib.net/

Synopsis

Simple compression and decompression

Extended api with control over compression parameters

data CompressParams #

The full set of parameters for compression. The defaults are defaultCompressParams.

The compressBufferSize is the size of the first output buffer containing the compressed data. If you know an approximate upper bound on the size of the compressed data then setting this parameter can save memory. The default compression output buffer size is 16k. If your extimate is wrong it does not matter too much, the default buffer size will be used for the remaining chunks.

defaultCompressParams :: CompressParams #

The default set of parameters for compression. This is typically used with the compressWith function with specific parameters overridden.

data DecompressParams #

The full set of parameters for decompression. The defaults are defaultDecompressParams.

The decompressBufferSize is the size of the first output buffer, containing the uncompressed data. If you know an exact or approximate upper bound on the size of the decompressed data then setting this parameter can save memory. The default decompression output buffer size is 32k. If your extimate is wrong it does not matter too much, the default buffer size will be used for the remaining chunks.

One particular use case for setting the decompressBufferSize is if you know the exact size of the decompressed data and want to produce a strict ByteString. The compression and deccompression functions use lazy ByteStrings but if you set the decompressBufferSize correctly then you can generate a lazy ByteString with exactly one chunk, which can be converted to a strict ByteString in O(1) time using concat . toChunks.

defaultDecompressParams :: DecompressParams #

The default set of parameters for decompression. This is typically used with the compressWith function with specific parameters overridden.

The compression parameter types

data CompressionLevel #

The compression level parameter controls the amount of compression. This is a trade-off between the amount of compression and the time required to do the compression.

Constructors

DefaultCompression

Deprecated: Use defaultCompression. CompressionLevel constructors will be hidden in version 0.7

NoCompression

Deprecated: Use noCompression. CompressionLevel constructors will be hidden in version 0.7

BestSpeed

Deprecated: Use bestSpeed. CompressionLevel constructors will be hidden in version 0.7

BestCompression

Deprecated: Use bestCompression. CompressionLevel constructors will be hidden in version 0.7

CompressionLevel Int 

Instances

Eq CompressionLevel # 
Show CompressionLevel # 
Generic CompressionLevel # 
type Rep CompressionLevel # 
type Rep CompressionLevel = D1 (MetaData "CompressionLevel" "Codec.Compression.Zlib.Stream" "zlib-0.6.1.2-BfeUVhBVvrx1Nvtzv6OD9c" False) ((:+:) ((:+:) (C1 (MetaCons "DefaultCompression" PrefixI False) U1) (C1 (MetaCons "NoCompression" PrefixI False) U1)) ((:+:) (C1 (MetaCons "BestSpeed" PrefixI False) U1) ((:+:) (C1 (MetaCons "BestCompression" PrefixI False) U1) (C1 (MetaCons "CompressionLevel" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Int))))))

defaultCompression :: CompressionLevel #

The default compression level is 6 (that is, biased towards higher compression at expense of speed).

noCompression :: CompressionLevel #

No compression, just a block copy.

bestSpeed :: CompressionLevel #

The fastest compression method (less compression)

bestCompression :: CompressionLevel #

The slowest compression method (best compression).

compressionLevel :: Int -> CompressionLevel #

A specific compression level between 0 and 9.

data Method #

The compression method

Constructors

Deflated

Deprecated: Use deflateMethod. Method constructors will be hidden in version 0.7

Instances

Bounded Method # 
Enum Method # 
Eq Method # 

Methods

(==) :: Method -> Method -> Bool #

(/=) :: Method -> Method -> Bool #

Ord Method # 
Show Method # 
Generic Method # 

Associated Types

type Rep Method :: * -> * #

Methods

from :: Method -> Rep Method x #

to :: Rep Method x -> Method #

type Rep Method # 
type Rep Method = D1 (MetaData "Method" "Codec.Compression.Zlib.Stream" "zlib-0.6.1.2-BfeUVhBVvrx1Nvtzv6OD9c" False) (C1 (MetaCons "Deflated" PrefixI False) U1)

deflateMethod :: Method #

'Deflate' is the only method supported in this version of zlib. Indeed it is likely to be the only method that ever will be supported.

data WindowBits #

This specifies the size of the compression window. Larger values of this parameter result in better compression at the expense of higher memory usage.

The compression window size is the value of the the window bits raised to the power 2. The window bits must be in the range 8..15 which corresponds to compression window sizes of 256b to 32Kb. The default is 15 which is also the maximum size.

The total amount of memory used depends on the window bits and the MemoryLevel. See the MemoryLevel for the details.

Constructors

WindowBits Int 
DefaultWindowBits

Deprecated: Use defaultWindowBits. WindowBits constructors will be hidden in version 0.7

Instances

defaultWindowBits :: WindowBits #

The default WindowBits is 15 which is also the maximum size.

windowBits :: Int -> WindowBits #

A specific compression window size, specified in bits in the range 8..15

data MemoryLevel #

The MemoryLevel parameter specifies how much memory should be allocated for the internal compression state. It is a tradoff between memory usage, compression ratio and compression speed. Using more memory allows faster compression and a better compression ratio.

The total amount of memory used for compression depends on the WindowBits and the MemoryLevel. For decompression it depends only on the WindowBits. The totals are given by the functions:

compressTotal windowBits memLevel = 4 * 2^windowBits + 512 * 2^memLevel
decompressTotal windowBits = 2^windowBits

For example, for compression with the default windowBits = 15 and memLevel = 8 uses 256Kb. So for example a network server with 100 concurrent compressed streams would use 25Mb. The memory per stream can be halved (at the cost of somewhat degraded and slower compressionby) by reducing the windowBits and memLevel by one.

Decompression takes less memory, the default windowBits = 15 corresponds to just 32Kb.

Constructors

DefaultMemoryLevel

Deprecated: Use defaultMemoryLevel. MemoryLevel constructors will be hidden in version 0.7

MinMemoryLevel

Deprecated: Use minMemoryLevel. MemoryLevel constructors will be hidden in version 0.7

MaxMemoryLevel

Deprecated: Use maxMemoryLevel. MemoryLevel constructors will be hidden in version 0.7

MemoryLevel Int 

Instances

Eq MemoryLevel # 
Show MemoryLevel # 
Generic MemoryLevel # 

Associated Types

type Rep MemoryLevel :: * -> * #

type Rep MemoryLevel # 
type Rep MemoryLevel = D1 (MetaData "MemoryLevel" "Codec.Compression.Zlib.Stream" "zlib-0.6.1.2-BfeUVhBVvrx1Nvtzv6OD9c" False) ((:+:) ((:+:) (C1 (MetaCons "DefaultMemoryLevel" PrefixI False) U1) (C1 (MetaCons "MinMemoryLevel" PrefixI False) U1)) ((:+:) (C1 (MetaCons "MaxMemoryLevel" PrefixI False) U1) (C1 (MetaCons "MemoryLevel" PrefixI False) (S1 (MetaSel (Nothing Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Int)))))

defaultMemoryLevel :: MemoryLevel #

The default memory level. (Equivalent to memoryLevel 8)

minMemoryLevel :: MemoryLevel #

Use minimum memory. This is slow and reduces the compression ratio. (Equivalent to memoryLevel 1)

maxMemoryLevel :: MemoryLevel #

Use maximum memory for optimal compression speed. (Equivalent to memoryLevel 9)

memoryLevel :: Int -> MemoryLevel #

A specific level in the range 1..9

data CompressionStrategy #

The strategy parameter is 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.

Constructors

DefaultStrategy

Deprecated: Use defaultStrategy. CompressionStrategy constructors will be hidden in version 0.7

Filtered

Deprecated: Use filteredStrategy. CompressionStrategy constructors will be hidden in version 0.7

HuffmanOnly

Deprecated: Use huffmanOnlyStrategy. CompressionStrategy constructors will be hidden in version 0.7

Instances

Bounded CompressionStrategy # 
Enum CompressionStrategy # 
Eq CompressionStrategy # 
Ord CompressionStrategy # 
Show CompressionStrategy # 
Generic CompressionStrategy # 
type Rep CompressionStrategy # 
type Rep CompressionStrategy = D1 (MetaData "CompressionStrategy" "Codec.Compression.Zlib.Stream" "zlib-0.6.1.2-BfeUVhBVvrx1Nvtzv6OD9c" False) ((:+:) (C1 (MetaCons "DefaultStrategy" PrefixI False) U1) ((:+:) (C1 (MetaCons "Filtered" PrefixI False) U1) (C1 (MetaCons "HuffmanOnly" PrefixI False) U1)))

defaultStrategy :: CompressionStrategy #

Use this default compression strategy for normal data.

filteredStrategy :: CompressionStrategy #

Use the filtered compression strategy for data produced by a filter (or predictor). Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect of this strategy is to force more Huffman coding and less string matching; it is somewhat intermediate between defaultCompressionStrategy and huffmanOnlyCompressionStrategy.

huffmanOnlyStrategy :: CompressionStrategy #

Use the Huffman-only compression strategy to force Huffman encoding only (no string match).