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 61

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 117

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 110

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 128

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 70

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
            @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
            @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