Class: Pdfrb::Filter::ASCII85Decode

Inherits:
Object
  • Object
show all
Includes:
Base
Defined in:
lib/pdfrb/filter/ascii_85_decode.rb

Overview

ASCII85Decode (s7.4.3). Adobe's base-85 encoding with EOD ~>. The z shorthand expands to four zero bytes.

Class Method Summary collapse

Class Method Details

.decoder(bytes, _parms, _document) ⇒ Object 



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# File 'lib/pdfrb/filter/ascii_85_decode.rb', line 13

def decoder(bytes, _parms, _document)
  out = +""
  group = []
  bytes.each_byte do |b|
    ch = b.chr
    case ch
    when "z"
      raise bad_byte(b) unless group.empty?

      out << "\x00\x00\x00\x00".b
    when "~"
      # EOD marker. Flush any partial group.
      break
    when " "
    else
      next unless (33..117).cover?(b)

      group << b
      if group.length == 5
        out << decode_group(group)
        group.clear
      end
    end
  end
  unless group.empty?
    n = group.length
    padded = group + [117] * (5 - n)
    decoded = decode_group(padded)
    out << decoded.byteslice(0, n - 1)
  end
  out.force_encoding(Encoding::BINARY)
end

.encoder(bytes, _parms, _document) ⇒ Object 



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# File 'lib/pdfrb/filter/ascii_85_decode.rb', line 46

def encoder(bytes, _parms, _document)
  out = +""
  bytes.bytes.each_slice(4) do |quad|
    padded = quad + [0] * (4 - quad.length)
    num = padded[0] << 24 | padded[1] << 16 | padded[2] << 8 | padded[3]
    chars = +""
    5.times { chars << (num % 85 + 33).chr; num /= 85 }
    chars.reverse!
    n = quad.length + 1
    out << chars.byteslice(0, n)
  end
  out << "~>"
  out.force_encoding(Encoding::BINARY)
end