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Origami::Filter::ASCII85

Class representing a filter used to encode and decode data written in base85 encoding.

Public Instance Methods

decode(string) click to toggle source

Decodes the given data encoded in base85.

string

The data to decode.

# File lib/origami/filters/ascii.rb, line 126
def decode(string)
  
  input = (string.include?(EOD) ? string[0..string.index(EOD) - 1] : string).delete(" \f\t\r\n\00"")
  
  i = 0
  result = ""
  while i < input.size do
    
    outblock = ""

    if input[i].ord == "z"[0].ord
      inblock = 0
      codelen = 1
    else
      
      inblock = 0
      codelen = 5
      
      if input.length - i < 5
        raise InvalidASCII85StringError.new("Invalid length", result) if input.length - i == 1
        
        addend = 5 - (input.length - i)
        input << "u" * addend
      else
        addend = 0
      end
    
      # Checking if this string is in base85
      5.times do |j|
        if input[i+j].ord > "u"[0].ord or input[i+j].ord < "!"[0].ord
          raise InvalidASCII85StringError.new(
            "Invalid character sequence: #{input[i,5].inspect}",
            result
          )
        else
          inblock += (input[i+j].ord - "!"[0].ord) * 85 ** (4 - j)
        end
      end
    
      
      raise InvalidASCII85StringError.new(
        "Invalid value (#{inblock}) for block #{input[i,5].inspect}",
        result
      ) if inblock >= 2**32
    
    end
  
    4.times do |p|
      c = inblock / 256 ** (3 - p)
      outblock << c.chr
      
      inblock -= c * 256 ** (3 - p)
    end
    
    if addend != 0
      outblock = outblock[0, 4 - addend]
    end
  
    result << outblock
    
    i = i + codelen
  end
  
  result
end
encode(stream) click to toggle source

Encodes given data into base85.

stream

The data to encode.

# File lib/origami/filters/ascii.rb, line 83
def encode(stream)
  
  i = 0
  code = ""
  input = stream.dup
  
  while i < input.size do
    
    if input.length - i < 4
      addend = 4 - (input.length - i)
      input << "\00"" * addend
    else
      addend = 0
    end
    
    inblock = (input[i].ord * 256**3 + input[i+1].ord * 256**2 + input[i+2].ord * 256 + input[i+3].ord)
    outblock = ""
    
    5.times do |p|
      c = inblock / 85 ** (4 - p)
      outblock << ("!"[0].ord + c).chr
      
      inblock -= c * 85 ** (4 - p)
    end
    
    outblock = "z" if outblock == "!!!!!" and addend == 0
    
    if addend != 0
      outblock = outblock[0,(4 - addend) + 1]
    end
    
    code << outblock
    
    i = i + 4
  end

  code
end

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