Class: HuffmanTable::Node

Inherits:
Object
  • Object
show all
Defined in:
lib/tasks/generate_huffman_table.rb

Defined Under Namespace

Classes: Transition

Constant Summary collapse

@@id =

rubocop:disable Style/ClassVars

0

Class Attribute Summary collapse

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(depth) ⇒ Node

Returns a new instance of Node.



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# File 'lib/tasks/generate_huffman_table.rb', line 18

def initialize(depth)
  @next = [nil, nil]
  @id = @@id
  @@id += 1 # rubocop:disable Style/ClassVars
  @final = false
  @depth = depth
end

Class Attribute Details

.root ⇒ Object (readonly)

Returns the value of attribute root.



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# File 'lib/tasks/generate_huffman_table.rb', line 146

def root
  @root
end

Instance Attribute Details

#depth ⇒ Object

Returns the value of attribute depth.



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# File 'lib/tasks/generate_huffman_table.rb', line 14

def depth
  @depth
end

#emit ⇒ Object

Returns the value of attribute emit.



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# File 'lib/tasks/generate_huffman_table.rb', line 14

def emit
  @emit
end

#final ⇒ Object

Returns the value of attribute final.



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# File 'lib/tasks/generate_huffman_table.rb', line 14

def final
  @final
end

#id ⇒ Object

Returns the value of attribute id.



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# File 'lib/tasks/generate_huffman_table.rb', line 16

def id
  @id
end

#next ⇒ Object

Returns the value of attribute next.



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# File 'lib/tasks/generate_huffman_table.rb', line 14

def next
  @next
end

#transitions ⇒ Object

Returns the value of attribute transitions.



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# File 'lib/tasks/generate_huffman_table.rb', line 15

def transitions
  @transitions
end

Class Method Details

.decode(input) ⇒ Object

Test decoder



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# File 'lib/tasks/generate_huffman_table.rb', line 150

def self.decode(input)
  emit = ''
  n = root
  nibbles = input.unpack('C*').flat_map { |b| [((b & 0xf0) >> 4), b & 0xf] }
  until nibbles.empty?
    nb = nibbles.shift
    t = n.transitions[nb]
    emit << t.emit
    n = t.node
  end
  unless n.final && nibbles.all? { |x| x == 0xf }
    puts "len = #{emit.size} n.final = #{n.final} nibbles = #{nibbles}"
  end
  emit
end

.generate_machine ⇒ Object 



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# File 'lib/tasks/generate_huffman_table.rb', line 55

def self.generate_machine
  generate_tree
  togo = Set[@root]
  @states = Set[@root]

  until togo.empty?
    node = togo.first
    togo.delete(node)

    next if node.transitions
    node.transitions = Array[1 << BITS_AT_ONCE]

    (1 << BITS_AT_ONCE).times do |input|
      n = node
      emit = ''
      (BITS_AT_ONCE - 1).downto(0) do |i|
        bit = (input & (1 << i)).zero? ? 0 : 1
        n = n.next[bit]
        next unless n.emit
        if n.emit == EOS
          emit = EOS # cause error on decoding
        else
          emit << n.emit.chr(Encoding::BINARY) unless emit == EOS
        end
        n = @root
      end
      node.transitions[input] = Transition.new(emit, n)
      togo << n
      @states << n
    end
  end
  puts "#{@states.size} states"
  @root
end

.generate_state_table ⇒ Object 



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# File 'lib/tasks/generate_huffman_table.rb', line 90

def self.generate_state_table
  generate_machine
  state_id = {}
  id_state = {}
  state_id[@root] = 0
  id_state[0] = @root
  max_final = 0
  id = 1
  (@states - [@root]).sort_by { |s| s.final ? 0 : 1 }.each do |s|
    state_id[s] = id
    id_state[id] = s
    max_final = id if s.final
    id += 1
  end

  File.open(File.expand_path('../http/2/huffman_statemachine.rb', File.dirname(__FILE__)), 'w') do |f|
    f.print <<HEADER
# Machine generated Huffman decoder state machine.
# DO NOT EDIT THIS FILE.

# The following task generates this file.
#   rake generate_huffman_table

module HTTP2
  module Header
class Huffman
  # :nodoc:
  MAX_FINAL_STATE = #{max_final}
  MACHINE = [
HEADER
    id.times do |i|
      n = id_state[i]
      f.print '        ['
      string = (1 << BITS_AT_ONCE).times.map do |t|
        transition = n.transitions.fetch(t)
        emit = transition.emit
        unless emit == EOS
          bytes = emit.bytes
          fail ArgumentError if bytes.size > 1
          emit = bytes.first
        end
        "[#{emit.inspect}, #{state_id.fetch(transition.node)}]"
      end.join(', ')
      f.print(string)
      f.print "],\n"
    end
    f.print <<TAILER
  ].each { |arr| arr.each { |subarr| subarr.each(&:freeze) }.freeze }.freeze
end
  end
end
TAILER
  end
end

.generate_tree ⇒ Object 



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# File 'lib/tasks/generate_huffman_table.rb', line 45

def self.generate_tree
  @root = new(0)
  HTTP2::Header::Huffman::CODES.each_with_index do |c, chr|
    code, len = c
    @root.add(code, len, chr)
  end
  puts "#{@@id} nodes"
  @root
end

Instance Method Details

#add(code, len, chr) ⇒ Object 



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# File 'lib/tasks/generate_huffman_table.rb', line 26

def add(code, len, chr)
  self.final = true if chr == EOS && @depth <= 7
  if len.zero?
    @emit = chr
  else
    bit = (code & (1 << (len - 1))).zero? ? 0 : 1
    node = @next[bit] ||= Node.new(@depth + 1)
    node.add(code, len - 1, chr)
  end
end