preflate-rs 0.6.3

Decompresses existing DEFLATE streams to allow for better compression (eg with ZStandard) while allowing the exact original binary DEFLATE stream to be recreated by detecting the parameters used during compression.
Documentation 
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/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the Apache License, Version 2.0. See LICENSE.txt in the project root for license information.
 *  This software incorporates material from third parties. See NOTICE.txt for details.
 *--------------------------------------------------------------------------------------------*/

use bitcode::{Decode, Encode};

use crate::estimator::add_policy_estimator::DictionaryAddPolicy;

#[derive(Encode, Decode, Debug, Copy, Clone, PartialEq, Eq, Default)]
pub enum MatchingType {
    #[default]
    Greedy,
    Lazy {
        good_length: u16,
        max_lazy: u16,
    },
}

pub struct PreflateParserConfig {
    pub match_type: MatchingType,
    pub dictionary_add_policy: DictionaryAddPolicy,

    /// if we get this length of a match we immediately stop searching for more
    pub nice_length: u32,
    pub max_chain: u32,
}

pub const ZLIB_PREFLATE_PARSER_SETTINGS: [PreflateParserConfig; 3] = [
    // these three levels are used by zlib

    // max speed, no lazy matches (the lazy field means
    // the maximum length that is added to the dictionary during
    // a match)
    PreflateParserConfig {
        match_type: MatchingType::Greedy,
        dictionary_add_policy: DictionaryAddPolicy::AddFirst(4),
        nice_length: 8,
        max_chain: 4,
    },
    PreflateParserConfig {
        match_type: MatchingType::Greedy,
        dictionary_add_policy: DictionaryAddPolicy::AddFirst(5),
        nice_length: 16,
        max_chain: 8,
    },
    PreflateParserConfig {
        match_type: MatchingType::Greedy,
        dictionary_add_policy: DictionaryAddPolicy::AddFirst(6),
        nice_length: 32,
        max_chain: 32,
    },
];

pub const SLOW_PREFLATE_PARSER_SETTINGS: [PreflateParserConfig; 6] = [
    // 4
    PreflateParserConfig {
        match_type: MatchingType::Lazy {
            good_length: 4,
            max_lazy: 4,
        },
        dictionary_add_policy: DictionaryAddPolicy::AddAll,
        nice_length: 16,
        max_chain: 16,
    },
    // 5
    PreflateParserConfig {
        match_type: MatchingType::Lazy {
            good_length: 8,
            max_lazy: 16,
        },
        dictionary_add_policy: DictionaryAddPolicy::AddAll,
        nice_length: 32,
        max_chain: 32,
    },
    // 6
    PreflateParserConfig {
        match_type: MatchingType::Lazy {
            good_length: 8,
            max_lazy: 16,
        },
        dictionary_add_policy: DictionaryAddPolicy::AddAll,
        nice_length: 128,
        max_chain: 128,
    },
    // 7
    PreflateParserConfig {
        match_type: MatchingType::Lazy {
            good_length: 8,
            max_lazy: 32,
        },
        dictionary_add_policy: DictionaryAddPolicy::AddAll,
        nice_length: 128,
        max_chain: 256,
    },
    // 8
    PreflateParserConfig {
        match_type: MatchingType::Lazy {
            good_length: 32,
            max_lazy: 128,
        },
        dictionary_add_policy: DictionaryAddPolicy::AddAll,
        nice_length: 258,
        max_chain: 1024,
    },
    // 9
    PreflateParserConfig {
        match_type: MatchingType::Lazy {
            good_length: 32,
            max_lazy: 258,
        },
        dictionary_add_policy: DictionaryAddPolicy::AddAll,
        nice_length: 258,
        max_chain: 4096,
    }, // max compression
];