zrip 0.1.2

Pure Rust zstd codec: Fast/DFast strategies (levels -7..4), COVER/FastCOVER dict builder
Documentation 
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#![forbid(unsafe_code)]

/// Match-finding strategy.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Strategy {
    /// Single hash table (levels -7 through 2).
    Fast,
    /// Short + long hash tables (levels 3-4).
    DFast,
}

/// Compression parameters for a specific level.
///
/// Obtain via [`level_params`] or construct directly for custom tuning.
/// Pass to [`compress_with_params`](crate::compress_with_params).
#[derive(Debug, Clone, Copy)]
pub struct LevelParams {
    pub strategy: Strategy,
    pub window_log: u32,
    pub hash_log: u32,
    pub search_log: u32,
    pub min_match: u32,
    pub target_length: u32,
    pub search_strength: u32,
}

/// Returns the compression parameters for a given level, or `None` if out of range.
pub fn level_params(level: i32) -> Option<LevelParams> {
    Some(match level {
        -7 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 13,
            search_log: 0,
            min_match: 4,
            target_length: 8,
            search_strength: 7,
        },
        -6 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 13,
            search_log: 0,
            min_match: 4,
            target_length: 7,
            search_strength: 7,
        },
        -5 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 13,
            search_log: 0,
            min_match: 4,
            target_length: 6,
            search_strength: 7,
        },
        -4 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 13,
            search_log: 0,
            min_match: 4,
            target_length: 5,
            search_strength: 7,
        },
        -3 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 13,
            search_log: 0,
            min_match: 4,
            target_length: 4,
            search_strength: 7,
        },
        -2 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 13,
            search_log: 0,
            min_match: 4,
            target_length: 3,
            search_strength: 7,
        },
        -1 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 13,
            search_log: 0,
            min_match: 4,
            target_length: 2,
            search_strength: 7,
        },
        1 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 19,
            hash_log: 14,
            search_log: 0,
            min_match: 7,
            target_length: 1,
            search_strength: 8,
        },
        2 => LevelParams {
            strategy: Strategy::Fast,
            window_log: 20,
            hash_log: 16,
            search_log: 0,
            min_match: 6,
            target_length: 1,
            search_strength: 8,
        },
        3 => LevelParams {
            strategy: Strategy::DFast,
            window_log: 21,
            hash_log: 17,
            search_log: 1,
            min_match: 5,
            target_length: 1,
            search_strength: 4,
        },
        4 => LevelParams {
            strategy: Strategy::DFast,
            window_log: 21,
            hash_log: 18,
            search_log: 1,
            min_match: 5,
            target_length: 1,
            search_strength: 4,
        },
        _ => return None,
    })
}