Module: LZ77

Defined in:
lib/lz77/decoder.rb

Class Method Summary collapse

Class Method Details

.decode(string) ⇒ Object

Decodes a string with LZ77 compression.

Params:

string: (String) encoded string

Returns: (String) decoded string



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# File 'lib/lz77/decoder.rb', line 10

def self.decode(string)
  result = ''
  i = 0

  while i < string.size
    b = string[i].ord

    if b == 0x00 or (0x09 <= b and b <= 0x7f)
      result << b.chr
    elsif 0x01 <= b and b <= 0x08
      b.times do |j|
        bb = string[i + j + 1]
        result << bb.chr
      end

      i += b
    elsif 0x80 <= b and b <= 0xbf
      b = (b << 8) + string[i + 1].ord
      s = result[(-1 * ((b & 0x3ff8) >> 3)), ((b & 0x0007) + 3)]

      s.each_byte do |bb|
        result << bb.chr
      end

      i += 1
    elsif 0xc0 <= b and b <= 0xff
      result << ' ' + (b ^ 0x80).chr
    end

    i += 1
  end

  return result
end