Class: Omnizip::Algorithms::PPMd7

Inherits:
Omnizip::Algorithm show all
Includes:
Constants
Defined in:
lib/omnizip/algorithms/ppmd7.rb,
lib/omnizip/algorithms/ppmd7/model.rb,
lib/omnizip/algorithms/ppmd7/context.rb,
lib/omnizip/algorithms/ppmd7/decoder.rb,
lib/omnizip/algorithms/ppmd7/encoder.rb,
lib/omnizip/algorithms/ppmd7/constants.rb,
lib/omnizip/algorithms/ppmd7/symbol_state.rb

Overview

PPMd7 compression algorithm

PPMd (Prediction by Partial Matching) is a statistical compression algorithm that excels at text compression. It uses context-based prediction to achieve high compression ratios on text files.

This implementation follows the PPMd7 specification as used in 7-Zip.

Defined Under Namespace

Modules: Constants Classes: Context, Decoder, Encoder, Model, SymbolState

Constant Summary

Constants included from Constants

Constants::ALPHABET_SIZE, Constants::BIN_SCALE, Constants::BOT_VALUE, Constants::DEFAULT_MEM_SIZE, Constants::DEFAULT_ORDER, Constants::INIT_ESCAPE_FREQ, Constants::INTERVAL, Constants::INT_BITS, Constants::MAX_FREQ, Constants::MAX_MEM_SIZE, Constants::MAX_ORDER, Constants::MAX_STATES, Constants::MIN_MEM_SIZE, Constants::MIN_ORDER, Constants::PERIOD_BITS, Constants::PROB_TOTAL, Constants::SEE_CONTEXTS, Constants::SUFFIX_CONTEXTS, Constants::TOP_VALUE, Constants::UNIT_ALLOC_SIZE, Constants::UNIT_SIZE

Instance Attribute Summary

Attributes inherited from Omnizip::Algorithm

#filter, #options

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Omnizip::Algorithm

inherited, #initialize, #with_filter

Constructor Details

This class inherits a constructor from Omnizip::Algorithm

Class Method Details

.metadata ⇒ AlgorithmMetadata

Algorithm metadata

Returns:

  • (AlgorithmMetadata) —

    Metadata describing this algorithm



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# File 'lib/omnizip/algorithms/ppmd7.rb', line 50

def self.metadata
  Models::AlgorithmMetadata.new.tap do |m|
    m.name = "ppmd7"
    m.description = "PPMd7 - Prediction by Partial Matching " \
                    "for statistical text compression"
    m.version = "1.0.0"
    m.supports_streaming = true
  end
end

Instance Method Details

#compress(input, output, options = {}) ⇒ void

This method returns an undefined value.

Compress data using PPMd7

Parameters:

  • input (IO, String) —

    Input data to compress

  • output (IO, String) —

    Output for compressed data

  • options (Hash) (defaults to: {}) —

    Compression options

Options Hash (options):

  • :model_order (Integer) —

    Context order (2-16)

  • :mem_size (Integer) —

    Memory size



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# File 'lib/omnizip/algorithms/ppmd7.rb', line 68

def compress(input, output, options = {})
  input = prepare_input(input)
  output = prepare_output(output)

  encoder = PPMd7::Encoder.new(output, options)
  encoder.encode_stream(input)
end

#decompress(input, output, options = {}) ⇒ void

This method returns an undefined value.

Decompress data using PPMd7

Parameters:

  • input (IO, String) —

    Compressed input data

  • output (IO, String) —

    Output for decompressed data

  • options (Hash) (defaults to: {}) —

    Decompression options

Options Hash (options):

  • :model_order (Integer) —

    Context order (2-16)

  • :mem_size (Integer) —

    Memory size



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# File 'lib/omnizip/algorithms/ppmd7.rb', line 84

def decompress(input, output, options = {})
  input = prepare_input(input)
  output = prepare_output(output)

  decoder = PPMd7::Decoder.new(input, options)
  result = decoder.decode_stream

  output.write(result)
end