round down a float

round_down.rb

class Float
  def round_down n=0
  s = self.to_s
  l = s.index('.') + 1 + n
  s.length <= l ? self : s[0,l].to_f
  end
end

# 2nd variant
class Float
  def round_down n=0
    n < 1 ? self.to_i.to_f : (self - 0.5 / 10**n).round(n)
  end
end

# 3rd variant
# from http://www.hans-eric.com/code-samples/ruby-floating-point-round-off/

class Float
  def round_to(x)
    (self * 10**x).round.to_f / 10**x
  end

  def ceil_to(x)
    (self * 10**x).ceil.to_f / 10**x
  end

  def floor_to(x)
    (self * 10**x).floor.to_f / 10**x
  end
end