Struct CompressionParameters

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pub struct CompressionParameters { /* private fields */ }

Expand description

Fully-resolved fine-grained compression parameters. Build through CompressionParameters::builder; pass to FrameCompressor::set_parameters or compress_with_parameters.

Wraps a base CompressionLevel plus the set of knobs that override it. A parameter set that overrides nothing is equivalent to compressing at its base level.

Implementations§

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impl CompressionParameters

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pub fn builder(level: CompressionLevel) -> CompressionParametersBuilder

Start a builder from a base compression level. Knobs left unset inherit that level’s resolved defaults.

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pub fn level(&self) -> CompressionLevel

The base compression level these parameters override.

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pub fn long_distance_matching_enabled(&self) -> bool

Whether long-distance matching is enabled.

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pub fn literal_compression_mode(&self) -> LiteralCompressionMode

How literals are entropy-coded (see LiteralCompressionMode).

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pub fn window_log_for( &self, source_size: Option<u64>, dictionary_size: usize, ) -> u32

The window, log2, the encoder gives a frame of source_size bytes (None = unknown) with dictionary_size bytes of dictionary content under these parameters: resolved exactly as the encoder resolves it.

use structured_zstd::encoding::{CompressionLevel, CompressionParameters};

let params = CompressionParameters::builder(CompressionLevel::Level(19))
    .window_log(23)
    .build()
    .unwrap();
assert_eq!(params.window_log_for(None, 0), 23);
assert!(params.window_log_for(Some(1000), 0) < 23);

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pub fn for_dictionary_frame(self, source_size: Option<u64>) -> Self

These parameters as a dictionary’s own, driving a frame of source_size bytes (None = unknown): an explicit window is raised to cover the source, as far as 512 KiB, as upstream raises a prepared dictionary’s window for a frame of known size (ZSTD_compressBegin_usingCDict_internal, zstd_compress.c:5844-5852). A window left to the level is resolved for the source and covers it.

use structured_zstd::encoding::{CompressionLevel, CompressionParameters};

let params = CompressionParameters::builder(CompressionLevel::Level(3))
    .window_log(10)
    .build()
    .unwrap();
let source = Some(1 << 20);
assert_eq!(params.for_dictionary_frame(source).window_log_for(source, 0), 19);
assert_eq!(params.for_dictionary_frame(None).window_log_for(None, 0), 10);