Class: Omnizip::Algorithms::Deflate64::LZ77Encoder

Inherits:
Object
  • Object
show all
Includes:
Constants
Defined in:
lib/omnizip/algorithms/deflate64/lz77_encoder.rb

Overview

LZ77 encoder with 64KB sliding window for Deflate64

Constant Summary

Constants included from Constants

Constants::BLOCK_TYPE_DYNAMIC, Constants::BLOCK_TYPE_FIXED, Constants::BLOCK_TYPE_STORED, Constants::DICTIONARY_SIZE, Constants::DISTANCE_CODES, Constants::END_OF_BLOCK, Constants::GOOD_MATCH, Constants::HASH_SHIFT, Constants::HASH_SIZE, Constants::LENGTH_CODES, Constants::LITERAL_CODES, Constants::MAX_CHAIN_LENGTH, Constants::MAX_DISTANCE, Constants::MAX_DISTANCE_CODE_LENGTH, Constants::MAX_LAZY_MATCH, Constants::MAX_LITERAL_CODE_LENGTH, Constants::MAX_MATCH_LENGTH, Constants::MIN_MATCH_LENGTH, Constants::NICE_MATCH

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(window_size = DICTIONARY_SIZE) ⇒ LZ77Encoder

Returns a new instance of LZ77Encoder.



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# File 'lib/omnizip/algorithms/deflate64/lz77_encoder.rb', line 12

def initialize(window_size = DICTIONARY_SIZE)
  @window_size = window_size
  @window = []
  @hash_table = {}
  @position = 0
end

Instance Attribute Details

#window_size ⇒ Object (readonly)

Returns the value of attribute window_size.



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# File 'lib/omnizip/algorithms/deflate64/lz77_encoder.rb', line 10

def window_size
  @window_size
end

Instance Method Details

#find_matches(data) ⇒ Array<Hash>

Find matches in data and return array of literals and match tokens

Parameters:

  • data (String) —

    Input data to compress

Returns:

  • (Array<Hash>) —

    Array of match tokens



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# File 'lib/omnizip/algorithms/deflate64/lz77_encoder.rb', line 23

def find_matches(data)
  tokens = []
  pos = 0

  while pos < data.bytesize
    match = find_longest_match(pos, data)

    if match && match[:length] >= MIN_MATCH_LENGTH
      tokens << {
        type: :match,
        length: match[:length],
        distance: match[:distance],
      }
      pos += match[:length]
    else
      tokens << {
        type: :literal,
        value: data.getbyte(pos),
      }
      pos += 1
    end

    update_window(data, pos)
  end

  tokens
end