Class: Omnizip::Algorithms::Zstandard::SequenceExecutor

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

Overview

Sequence executor (RFC 8878 Section 3.1.2.2.3)

Executes decoded sequences to produce output.

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

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ SequenceExecutor

Initialize with default repeat offsets



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# File 'lib/omnizip/algorithms/zstandard/sequences.rb', line 270

def initialize
  @repeat_offsets = DEFAULT_REPEAT_OFFSETS.dup
end

Class Method Details

.execute(literals, sequences) ⇒ String

Execute sequences to produce decompressed output

Parameters:

  • literals (String) —

    Decoded literals

  • sequences (Array<Hash>) —

    Decoded sequences

Returns:

  • (String) —

    Decompressed output



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# File 'lib/omnizip/algorithms/zstandard/sequences.rb', line 264

def self.execute(literals, sequences)
  executor = new
  executor.execute(literals, sequences)
end

Instance Method Details

#execute(literals, sequences) ⇒ String

Execute sequences

Parameters:

  • literals (String) —

    Decoded literals

  • sequences (Array<Hash>) —

    Decoded sequences

Returns:

  • (String) —

    Decompressed output



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# File 'lib/omnizip/algorithms/zstandard/sequences.rb', line 279

def execute(literals, sequences)
  output = String.new(encoding: Encoding::BINARY)
  lit_pos = 0

  sequences.each do |seq|
    ll = seq[:literals_length] || 0
    ml = seq[:match_length] || 0
    offset_code = seq[:offset] || 0

    # Copy literals
    if ll.positive? && lit_pos < literals.length
      copy_len = [ll, literals.length - lit_pos].min
      output << literals.slice(lit_pos, copy_len)
      lit_pos += copy_len
    end

    # Handle match
    if ml.positive?
      offset = resolve_offset(offset_code)

      if offset.positive? && offset <= output.length
        # Copy match from output history
        match_str = output.slice(-offset, [ml, offset].min) || ""
        # If match is longer than offset, we need to copy byte by byte
        while match_str.length < ml && output.length.positive?
          match_str << match_str[-offset] if offset <= match_str.length
        end
        output << match_str.slice(0, ml)
      end
    end
  end

  # Copy remaining literals (last sequence has no match)
  if lit_pos < literals.length
    output << literals.slice(lit_pos..-1)
  end

  output
end