64進数的な

integer_to_s64.rb

# -*- coding: utf-8 -*-
 
class Integer
  S64_MAP = ('0'..'9').to_a +
    ('a'..'z').to_a +
    ('A'..'Z').to_a +
    ['_']
 
  def to_s64
    s, i, base, negative = '', self, S64_MAP.size, false
    return '0' if i == 0
    if i < 0
      i = -i
      negative = true
    end
    while i > 0
      s << S64_MAP[i % base]
      i /= base
    end
    s << '-' if negative
    s.reverse
  end
end