Fast Base32 Implementation in Pure Ruby

base32.rb

module Base32
  TABLE = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'
  TABLE_REVERSE = Array.new(256)
  TABLE.each_byte.with_index{|c, i| TABLE_REVERSE[c.ord] = i}
  TABLE_REVERSE.freeze
  PADDING = [0, 0, 0, 0, 0].pack('C*').freeze

  def self.encode32(str, padding: false)
    bytes = String.new(str, encoding: Encoding::ASCII_8BIT)
    bytesize = bytes.bytesize
    bytes << PADDING
    chunksize = (bytesize + 4) / 5
    ret = String.new(capacity: chunksize * 8)
    chunksize.times do |i|
      s = i * 5
      b1 = bytes[s].ord
      b2 = bytes[s + 1].ord
      b3 = bytes[s + 2].ord
      b4 = bytes[s + 3].ord
      b5 = bytes[s + 4].ord
      ret << TABLE[b1 >> 3]
      ret << TABLE[b1 << 2 & 0x1c | b2 >> 6]
      ret << TABLE[b2 >> 1 & 0x1f]
      ret << TABLE[b2 << 4 & 0x10 | b3 >> 4]
      ret << TABLE[b3 << 1 & 0x1e | b4 >> 7]
      ret << TABLE[b4 >> 2 & 0x1f]
      ret << TABLE[b4 << 3 & 0x18 | b5 >> 5]
      ret << TABLE[b5 & 0x1f]
    end
    if padding
      (((bytesize * 8 + 4) / 5)...(ret.size)).each do |i|
        ret[i] = '='
      end
      ret
    else
      ret[0, (bytesize * 8 + 4) / 5]
    end
  end

  def self.decode32(str)
    ret = String.new(capacity: (str.bytesize * 5 + 3) / 8)
    current = 0
    pos = 0
    str.each_byte do |b|
      c = TABLE_REVERSE[b]
      break unless c

      case pos
      when 0
        current = c << 3
        pos = 5
      when 1, 2
        current |= c << (3 - pos)
        pos += 5
      when 3
        current |= c
        ret << current.ord
        pos = 0
      else
        current |= c >> (pos - 3)
        ret << current.ord
        current = (c << (11 - pos)) & 0xff
        pos -= 3
      end
    end
    ret
  end
end