Struct deflate::CompressionOptions [] [src]

pub struct CompressionOptions {
    pub max_hash_checks: u16,
    pub lazy_if_less_than: u16,
    pub matching_type: MatchingType,
    pub special: SpecialOptions,
}

A struct describing the options for a compressor or compression function.

These values are not stable and still subject to change!

Fields

The maximum number of checks to make in the hash table for matches.

Higher numbers mean slower, but better compression. Very high (say >1024) values will impact compression speed a lot. The maximum match length is 215, so values higher than this won't make any difference, and will be truncated to 215 by the compression function/writer.

Default value: 128

Only lazy match if we have a length less than this value.

Higher values degrade compression slightly, but improve compression speed.

As the maximum length of a match is 258, values higher than this will have no further effect.

Whether to use lazy or greedy matching.

Lazy matching will provide better compression, at the expense of compression speed.

As a special case, if max_hash_checks is set to 0, and matching_type is set to lazy, compression using only run-length encoding (i.e maximum match distance of 1) is performed. (This may be changed in the future but is defined like this at the moment to avoid API breakage.

See MatchingType

Force fixed/stored blocks (Not implemented yet). * Default value: SpecialOptions::Normal

Methods

impl CompressionOptions
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Returns compression settings rouhgly corresponding to the HIGH(9) setting in miniz.

Returns a fast set of compression settings

Ideally this should roughly correspond to the FAST(1) setting in miniz. However, that setting makes miniz use a somewhat different algorhithm, so currently hte fast level in this library is slower and better compressing than the corresponding level in miniz.

Returns a set of compression settings that makes the compressor only compress using huffman coding. (Ignoring any length/distance matching)

This will normally have the worst compression ratio (besides only using uncompressed data), but may be the fastest method in some cases.

Returns a set of compression settings that makes the compressor compress only using run-length encoding (i.e only looking for matches one byte back).

This is very fast, but tends to compress worse than looking for more matches using hash chains that the slower settings do. Works best on data that has runs of equivialent bytes, like binary or simple images, less good for text.

Trait Implementations

impl Copy for CompressionOptions
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impl Clone for CompressionOptions
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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl Debug for CompressionOptions
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Formats the value using the given formatter.

impl Eq for CompressionOptions
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impl PartialEq for CompressionOptions
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This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

impl Hash for CompressionOptions
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Feeds this value into the given [Hasher]. Read more

Feeds a slice of this type into the given [Hasher]. Read more

impl Default for CompressionOptions
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Returns the options describing the default compression level.

impl From<Compression> for CompressionOptions
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Performs the conversion.