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fix(zstd): fastest level now does compression #357

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Merged
NobodyXu merged 1 commit into from
Jul 13, 2025
Merged

fix(zstd): fastest level now does compression #357

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9 changes: 8 additions & 1 deletion src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -254,8 +254,15 @@ impl Level {
#[cfg(feature = "zstd")]
fn into_zstd(self) -> i32 {
let (fastest, best) = libzstd::compression_level_range().into_inner();

// NOTE: zstd's "fastest" level is -131072 which can create outputs larger than inputs.
// This library chooses a "fastest" level which has a more-or-less equivalent compression
// ratio to gzip's fastest mode. We still allow precise levels to go negative.
// See discussion in https://github.com/Nullus157/async-compression/issues/352
const OUR_FASTEST: i32 = 1;

match self {
Self::Fastest => fastest,
Self::Fastest => OUR_FASTEST,
Self::Best => best,
Self::Precise(quality) => quality.clamp(fastest, best),
Self::Default => libzstd::DEFAULT_COMPRESSION_LEVEL,
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