Class: Omnizip::Algorithms::Zstandard::LiteralsDecoder

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

Overview

Literals section decoder (RFC 8878 Section 3.1.1.3.1)

Decodes the literals section of a compressed block. Can be raw, RLE, Huffman compressed, or treeless.

Constant Summary

Constants included from Constants

Constants::BLOCK_HEADER_SIZE, Constants::BLOCK_MAX_SIZE, Constants::BLOCK_TYPE_COMPRESSED, Constants::BLOCK_TYPE_RAW, Constants::BLOCK_TYPE_RESERVED, Constants::BLOCK_TYPE_RLE, Constants::BUFFER_SIZE, Constants::DEFAULT_LEVEL, Constants::DEFAULT_REPEAT_OFFSETS, Constants::FSE_MAX_ACCURACY_LOG, Constants::FSE_MIN_ACCURACY_LOG, Constants::HUFFMAN_MAX_BITS, Constants::HUFFMAN_MAX_CODE_LENGTH, Constants::HUFFMAN_MAX_LOG, Constants::HUFFMAN_STANDARD_TABLE_SIZE, Constants::LITERALS_BLOCK_COMPRESSED, Constants::LITERALS_BLOCK_RAW, Constants::LITERALS_BLOCK_RLE, Constants::LITERALS_BLOCK_TREELESS, Constants::LITERALS_LENGTH_ACCURACY_LOG, Constants::LITERAL_LENGTH_TABLE, Constants::MAGIC_BYTES, Constants::MAGIC_NUMBER, Constants::MATCH_LENGTH_ACCURACY_LOG, Constants::MATCH_LENGTH_TABLE, Constants::MAX_LEVEL, Constants::MIN_LEVEL, Constants::MODE_FSE, Constants::MODE_PREDEFINED, Constants::MODE_REPEAT, Constants::MODE_RLE, Constants::OFFSET_ACCURACY_LOG, Constants::PREDEFINED_LL_DISTRIBUTION, Constants::PREDEFINED_ML_DISTRIBUTION, Constants::PREDEFINED_OFFSET_DISTRIBUTION, Constants::REPEAT_OFFSET_1, Constants::REPEAT_OFFSET_2, Constants::REPEAT_OFFSET_3, Constants::SKIPPABLE_MAGIC_BASE, Constants::SKIPPABLE_MAGIC_MASK, Constants::WINDOW_LOG_MAX, Constants::WINDOW_LOG_MIN

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(input, previous_table = nil) ⇒ LiteralsDecoder

Initialize decoder

Parameters:

  • input (IO) —

    Input stream

  • previous_table (Huffman, nil) (defaults to: nil) —

    Previous Huffman table



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# File 'lib/omnizip/algorithms/zstandard/literals.rb', line 54

def initialize(input, previous_table = nil)
  @input = input
  @previous_table = previous_table
  @literals = String.new(encoding: Encoding::BINARY)
  @huffman_table = previous_table
end

Instance Attribute Details

#huffman_table ⇒ Huffman? (readonly)

Returns Huffman table for future treeless blocks.

Returns:

  • (Huffman, nil) —

    Huffman table for future treeless blocks



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# File 'lib/omnizip/algorithms/zstandard/literals.rb', line 37

def huffman_table
  @huffman_table
end

#literals ⇒ String (readonly)

Returns Decoded literals.

Returns:

  • (String) —

    Decoded literals



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# File 'lib/omnizip/algorithms/zstandard/literals.rb', line 34

def literals
  @literals
end

Class Method Details

.decode(input, previous_table = nil) ⇒ LiteralsDecoder

Parse and decode literals section

Parameters:

  • input (IO) —

    Input stream positioned at literals section

  • previous_table (Huffman, nil) (defaults to: nil) —

    Previous Huffman table (for treeless)

Returns:



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# File 'lib/omnizip/algorithms/zstandard/literals.rb', line 44

def self.decode(input, previous_table = nil)
  decoder = new(input, previous_table)
  decoder.decode_section
  decoder
end

Instance Method Details

#decode_section ⇒ void

This method returns an undefined value.

Decode the literals section



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# File 'lib/omnizip/algorithms/zstandard/literals.rb', line 64

def decode_section
  # Read literals header (1-3 bytes)
  header1 = @input.read(1).ord
  block_type = (header1 >> 6) & 0x03

  case block_type
  when LITERALS_BLOCK_RAW
    decode_raw(header1)
  when LITERALS_BLOCK_RLE
    decode_rle(header1)
  when LITERALS_BLOCK_COMPRESSED
    decode_compressed(header1)
  when LITERALS_BLOCK_TREELESS
    decode_treeless(header1)
  end
end