Method: PDF::Reader::LZW::BitStream#read

Defined in:
lib/pdf/reader/lzw.rb

#read ⇒ Object 



37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
 
# File 'lib/pdf/reader/lzw.rb', line 37

def read
  bits_left_in_chunk = @bits_in_chunk
  chunk = -1
  while bits_left_in_chunk > 0 and @current_pos < @data.size
    chunk = 0 if chunk < 0
    codepoint = @data[@current_pos, 1].unpack("C*")[0]
    current_byte = codepoint & (2**@bits_left_in_byte - 1) #clear consumed bits
    dif = bits_left_in_chunk - @bits_left_in_byte
    if dif > 0 then  current_byte <<= dif
    elsif dif < 0 then  current_byte >>= dif.abs
    end
    chunk |= current_byte #add bits to result
    bits_left_in_chunk = if dif >= 0 then dif else 0 end
    @bits_left_in_byte = if dif < 0 then dif.abs else 0 end
    if @bits_left_in_byte.zero? #next byte
      @current_pos += 1
      @bits_left_in_byte = 8
    end
  end
  chunk
end