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module FastImageParsing
class Jxlc # :nodoc:
attr_reader :width, :height
LENGTHS = [9, 13, 18, 30]
MULTIPLIERS = [1, 1.2, Rational(4, 3), 1.5, Rational(16, 9), 1.25, 2]
def initialize(stream)
@stream = stream
@width, @height´ = nil
@bit_counter = 0
parse_jxlc
end
def parse_jxlc
@words = @stream.read(6)[2..5].unpack('vv')
# small mode allows for values <= 256 that are divisible by 8
small = get_bits(1)
if small == 1
y = (get_bits(5) + 1) * 8
x = x_from_ratio(y)
if !x
x = (get_bits(5) + 1) * 8
end
@width, @height = x, y
return
end
len = LENGTHS[get_bits(2)]
y = get_bits(len) + 1
x = x_from_ratio(y)
if !x
len = LENGTHS[get_bits(2)]
x = get_bits(len) + 1
end
@width, @height = x, y
end
def get_bits(size)
if @words.size < (@bit_counter + size) / 16 + 1
@words += @stream.read(4).unpack('vv')
end
dest_pos = 0
dest = 0
size.times do
word = @bit_counter / 16
source_pos = @bit_counter % 16
dest |= ((@words[word] & (1 << source_pos)) > 0 ? 1 : 0) << dest_pos
dest_pos += 1
@bit_counter += 1
end
dest
end
def x_from_ratio(y)
ratio = get_bits(3)
if ratio == 0
return nil
else
return (y * MULTIPLIERS[ratio - 1]).to_i
end
end
end
def parse_size_for_jxl
if @stream.peek(2) == "\xFF\x0A".b
JXL.new(@stream).read_size_header
else
bmff = IsoBmff.new(@stream)
bmff.width_and_height
end
end
end
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