base62.rb

module Base62
  CHARS = ('a'..'z').to_a + ('A'..'Z').to_a + ('0'..'9').to_a
  MOD = CHARS.size # 62

  module_function

  def encode_packed(string)
    encode(string.unpack('H*').at(0).to_i(16))
  end

  def encode(fixnum)
    out = []

    while fixnum > 0
      fixnum, r = fixnum.divmod(MOD)
      out.unshift CHARS[r]
    end

    out.join
  end

  def decode_packed(string)
    [decode(string).to_s(16)].pack('H*')
  end

  def decode(string)
    out = 0
    string.scan(/./mn){|c| out = out * MOD + CHARS.index(c) }
    out
  end
end

eval(DATA.read) if __FILE__ == $0
__END__
require 'bacon'
Bacon.summary_on_exit

describe Base62 do
  should 'encode' do
    Base62.encode(999).should == 'qh'
  end

  should 'decode' do
    Base62.decode('qh').should == 999
  end

  should 'encode_packed' do
    Base62.encode_packed('Hello, World! - snake_case').
      should == "ntNEbEbmiA66ycSlgi04nDKpZl1YZM1N7sf"
  end

  should 'decode_packed' do
    Base62.decode_packed("ntNEbEbmiA66ycSlgi04nDKpZl1YZM1N7sf").
      should == 'Hello, World! - snake_case'
  end
end