Class: Origami::Filter::ASCII85

Inherits:
Object
  • Object
show all
Includes:
Origami::Filter
Defined in:
lib/origami/filters/ascii.rb

Overview

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

Constant Summary collapse

EOD =

:nodoc:

"~>"

Instance Method Summary collapse

Instance Method Details

#decode(string) ⇒ Object

Decodes the given data encoded in base85.

string

The data to decode.



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# File 'lib/origami/filters/ascii.rb', line 125

def decode(string)
  
  input = (string.include?(EOD) ? string[0..string.index(EOD) - 1] : string).delete(" \f\t\r\n\0")
  
  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, "Invalid length" 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, "Invalid character sequence: #{input[i,5].inspect}"
        else
          inblock += (input[i+j].ord - "!"[0].ord) * 85 ** (4 - j)
        end
      end
    
      if inblock >= 2**32
        raise InvalidASCII85StringError, "Invalid value (#{inblock}) for block #{input[i,5].inspect}"
      end
    
    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) ⇒ Object

Encodes given data into base85.

stream

The data to encode.



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# File 'lib/origami/filters/ascii.rb', line 82

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 << "\0" * 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