Class: Omnizip::Formats::Rar::Rar5::Compression::Lzss::HuffmanTable

Inherits:
Object
  • Object
show all
Defined in:
lib/omnizip/formats/rar/rar5/compression/lzss.rb

Overview

Huffman decode table

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(size) ⇒ HuffmanTable

Returns a new instance of HuffmanTable.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 209

def initialize(size)
  @size = size
  @decode_len = Array.new(16, 0)
  @decode_pos = Array.new(16, 0)
  @decode_num = Array.new(size, 0)
  @quick_bits = 0
  @quick_len = Array.new(65536, 0)
  @quick_num = Array.new(65536, 0)
end

Instance Attribute Details

#decode_len ⇒ Object (readonly)

Returns the value of attribute decode_len.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 207

def decode_len
  @decode_len
end

#decode_num ⇒ Object (readonly)

Returns the value of attribute decode_num.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 207

def decode_num
  @decode_num
end

#decode_pos ⇒ Object (readonly)

Returns the value of attribute decode_pos.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 207

def decode_pos
  @decode_pos
end

#size ⇒ Object (readonly)

Returns the value of attribute size.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 207

def size
  @size
end

Instance Method Details

#build(bit_lengths) ⇒ Object

Build decode tables from bit lengths Based on libarchive's create_decode_tables()



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 221

def build(bit_lengths)
  # Count codes for each bit length
  len_count = Array.new(16, 0)
  bit_lengths.each do |len|
    len_count[len] += 1 if len.positive? && len < 16
  end

  # Calculate decode_len and decode_pos
  @decode_pos[0] = 0
  @decode_len[0] = 0

  upper_limit = 0
  (1..15).each do |i|
    upper_limit = (upper_limit + len_count[i]) << 1
    @decode_len[i] = upper_limit << (16 - i)
    @decode_pos[i] = @decode_pos[i - 1] + len_count[i - 1]
  end

  # Fill decode_num
  decode_pos_copy = @decode_pos.dup
  bit_lengths.each_with_index do |len, symbol|
    next unless len.positive? && len < 16

    pos = decode_pos_copy[len]
    @decode_num[pos] = symbol if pos < @size
    decode_pos_copy[len] += 1
  end

  # Build quick lookup table
  @quick_bits = 10 # Use 10 bits for quick lookup
  build_quick_table(bit_lengths)

  true
end

#decode(bit_reader) ⇒ Object

Decode a symbol from bit reader



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 257

def decode(bit_reader)
  # Read 16 bits for lookup
  bit_field = bit_reader.read_bits(16)
  return nil if bit_field.nil?

  # Quick lookup
  if @quick_len[bit_field].positive?
    bit_reader.skip_bits(@quick_len[bit_field])
    return @quick_num[bit_field]
  end

  # Full decode
  bits = 15
  (1..14).each do |i|
    if bit_field < @decode_len[i]
      bits = i
      break
    end
  end

  bit_reader.skip_bits(bits)

  dist = bit_field - @decode_len[bits - 1]
  dist >>= (16 - bits)
  pos = @decode_pos[bits] + dist

  pos < @size ? @decode_num[pos] : 0
end