Class Gz.deflate

Description

This class interfaces with the compression routines in the libz library.

Note

This class is only available if libz was available and found when Pike was compiled.

See also

Gz.inflate(), Gz.compress(), Gz.uncompress()

Method create

Gz.deflate Gz.deflate(int(-9..9)|void level, int|void strategy, int(8..15)|void window_size)
Gz.deflate Gz.deflate(mapping options)

Description

This function can also be used to re-initialize a Gz.deflate object so it can be re-used.

If a mapping is passed as the only argument, it will accept the parameters described below as indices, and additionally it accepts a string as dictionary.

Parameter level

Indicates the level of effort spent to make the data compress well. Zero means no packing, 2-3 is considered 'fast', 6 is default and higher is considered 'slow' but gives better packing.

If the argument is negative, no headers will be emitted. This is needed to produce ZIP-files, as an example. The negative value is then negated, and handled as a positive value.

Parameter strategy

The strategy to be used when compressing the data. One of the following.

DEFAULT_STRATEGY	The default strategy as selected in the zlib library.
FILTERED	This strategy is intented for data created by a filter or predictor and will put more emphasis on huffman encoding and less on LZ string matching. This is between DEFAULT_STRATEGY and HUFFMAN_ONLY.
RLE	This strategy is even closer to the HUFFMAN_ONLY in that it only looks at the latest byte in the window, i.e. a window size of 1 byte is sufficient for decompression. This mode is not available in all zlib versions.
HUFFMAN_ONLY	This strategy will turn of string matching completely, only doing huffman encoding. Window size doesn't matter in this mode and the data can be decompressed with a zero size window.
FIXED	In this mode dynamic huffman codes are disabled, allowing for a simpler decoder for special applications. This mode is not available in all zlib versions.

Parameter window_size

Defines the size of the LZ77 window from 256 bytes to 32768 bytes, expressed as 2^x.