BitIO

gistfile1.rb

#
# BitIO utility.
#

class BitIO
  include Enumerable
  attr_accessor :bytepos, :bitpos

  def initialize(text)
    @text = text
    @bytepos = 0   # Current byte position.
    @bitpos = -1   # Current bit position ([7,6,5,4,3,2,1,0]).
    @buffer = 0    # Contains current byte.
  end

  def self.open(text)
    self.new text
  end

private
  def readbuf
    return @buffer = nil if @text.bytesize <= @bytepos

    @buffer = @text.getbyte(@bytepos)
    @bytepos += 1
    @bitpos = 7
  end

public
  def eof?
    readbuf if @bitpos < 0
    @buffer == nil
  end

  # Reads a bit.
  def getbit
    readbuf if @bitpos < 0
    return nil if @buffer == nil

    mask = 0x1
    bit = (@buffer >> @bitpos) & mask
    @bitpos -= 1

    bit.to_s
  end

  # Reads n bits.
  def readbits(n)
    ret = ""
    n.times do
      ret << getbit.to_s
    end
    ret
  end

  def write str
    @text <<= str
  end

  def rewind
    @bytepos = 0
    @bitpos = -1
  end

  def each
    while !eof? do
      yield getbit
    end
  end

#  def to_s
#    @text
#  end
end

=begin
puts "[a] %08b" % "a".getbyte(0)
puts "[b] %08b" % "b".getbyte(0)
puts "[c] %08b" % "c".getbyte(0)
print "\n"

bitio = BitIO.new("abc")

puts "Init \"abc\""
print "Read all: "
while (bit = bitio.getbit) != nil do
  print bit
end
print "\n\n"

bitio.write("aa"); puts "write \"aa\""

print "Read all: ";
bitio.each do |b|
  print b
end
print "\n\n"

bitio.rewind; puts "rewind"

print "Read all: "
bitio.each do |b|
  print b
end
print "\n\n"

bitio.rewind; puts "rewind"

puts "Read 4 bits: #{bitio.readbits 4}"
puts "Read 8 bits: #{bitio.readbits 8}"
puts "Read 5 bits: #{bitio.readbits 5}"
=end