Class: Origami::Filter::Utils::BitWriter

Inherits:
Object
  • Object
show all
Defined in:
lib/origami/filters.rb

Overview

Class used to forge a String from a stream of bits. Internally used by some filters.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ BitWriter

Returns a new instance of BitWriter.



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# File 'lib/origami/filters.rb', line 53

def initialize
  @data = ''
  @last_byte = nil
  @ptr_bit = 0
end

Instance Method Details

#final ⇒ Object

Finalizes the stream.



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# File 'lib/origami/filters.rb', line 109

def final
  @data << @last_byte.chr if @last_byte
  @last_byte = nil
  @p = 0

  self
end

#size ⇒ Object

Returns the data size in bits.



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# File 'lib/origami/filters.rb', line 102

def size
  (@data.size << 3) + @ptr_bit
end

#to_s ⇒ Object

Outputs the stream as a String.



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# File 'lib/origami/filters.rb', line 120

def to_s
  @data.dup
end

#write(data, length) ⇒ Object

Writes data represented as Fixnum to a length number of bits.



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# File 'lib/origami/filters.rb', line 62

def write(data, length)
  return BitWriterError, "Invalid data length" unless length > 0 and (1 << length) > data

  # optimization for aligned byte writing
  if length == 8 and @last_byte.nil? and @ptr_bit == 0
    @data << data.chr
    return self
  end

  while length > 0
    if length >= 8 - @ptr_bit
      length -= 8 - @ptr_bit
      @last_byte = 0 unless @last_byte
      @last_byte |= (data >> length) & ((1 << (8 - @ptr_bit)) - 1)

      data &= (1 << length) - 1
      @data << @last_byte.chr
      @last_byte = nil
      @ptr_bit = 0
    else
      @last_byte = 0 unless @last_byte
      @last_byte |= (data & ((1 << length) - 1)) << (8 - @ptr_bit - length)
      @ptr_bit += length
      
      if @ptr_bit == 8
        @data << @last_byte.chr
        @last_byte = nil
        @ptr_bit = 0
      end
      
      length = 0
    end
  end

  self
end