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# coding: utf-8
# typed: strict
# frozen_string_literal: true
module PDF
class Reader
# A general class for decoding LZW compressed data. LZW can be
# used in PDF files to compresses streams, usually for image data sourced
# from a TIFF file.
#
# See the following links for more information:
#
# ref http://www.fileformat.info/format/tiff/corion-lzw.htm
# ref http://marknelson.us/1989/10/01/lzw-data-compression/
#
# The PDF spec also has some data on the algorithm.
#
class LZW # :nodoc:
# Wraps an LZW encoded string
class BitStream # :nodoc:
#: (String, Integer) -> void
def initialize(data, bits_in_chunk)
@data = data
@data.force_encoding("BINARY")
@current_pos = 0 #: Integer
@bits_left_in_byte = 8 #: Integer
@bits_in_chunk = 0 #: Integer
set_bits_in_chunk(bits_in_chunk)
end
#: (Integer) -> void
def set_bits_in_chunk(bits_in_chunk)
raise MalformedPDFError, "invalid LZW bits" if bits_in_chunk < 9 || bits_in_chunk > 12
@bits_in_chunk = bits_in_chunk
end
#: () -> Integer
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].to_s.unpack("C*")[0].to_i
current_byte = codepoint & (2**@bits_left_in_byte - 1).to_i #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
end
CODE_EOD = 257 #: Integer #end of data
CODE_CLEAR_TABLE = 256 #: Integer #clear table
# stores de pairs code => string
class StringTable
#: Integer
attr_reader :string_table_pos
#: () -> void
def initialize
@data = Hash.new #: Hash[Integer, String]
# The initial code
@string_table_pos = 258 #: Integer
end
#if code less than 258 return fixed string
#: (Integer) -> String?
def [](key)
if key > 257
@data[key]
else
key.chr
end
end
#: (String) -> void
def add(string)
@data.store(@string_table_pos, string)
@string_table_pos += 1
end
end
# Decompresses a LZW compressed string.
#
#: (String) -> String
def self.decode(data)
stream = BitStream.new(data.to_s, 9) # size of codes between 9 and 12 bits
string_table = StringTable.new
result = "".dup
until (code = stream.read) == CODE_EOD
if code == CODE_CLEAR_TABLE
stream.set_bits_in_chunk(9)
string_table = StringTable.new
code = stream.read
break if code == CODE_EOD
result << string_table[code]
old_code = code
else
string = string_table[code]
if string
result << string
string_table.add create_new_string(string_table, old_code, code)
old_code = code
else
new_string = create_new_string(string_table, old_code, old_code)
result << new_string
string_table.add new_string
old_code = code
end
#increase de size of the codes when limit reached
if string_table.string_table_pos == 511
stream.set_bits_in_chunk(10)
elsif string_table.string_table_pos == 1023
stream.set_bits_in_chunk(11)
elsif string_table.string_table_pos == 2047
stream.set_bits_in_chunk(12)
end
end
end
result
end
#: (PDF::Reader::LZW::StringTable, Integer?, Integer?) -> String
def self.create_new_string(string_table, some_code, other_code)
raise MalformedPDFError, "invalid LZW data" if some_code.nil? || other_code.nil?
item_one = string_table[some_code]
item_two = string_table[other_code]
if item_one && item_two
item_one + item_two.chr
else
raise MalformedPDFError, "invalid LZW data"
end
end
private_class_method :create_new_string
end
end
end
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