no-div.rb

no-div.rb

#!/usr/bin/env ruby
#
#

class FixedNum
  attr_accessor :num, :rem
  def initialize num, rem=0
    @num = num ; @rem = rem ; self
  end

  def inspect
    @rem == 0 ? @num.to_s : @num.to_s + 'r' + @rem.to_s
  end
  def to_s  ; self.inspect ; end

  def ==(v)
    v.num == @num && v.rem == @rem
  end
end

class Fixnum

  def my_div divisor
    return nil if divisor == 0
    return 0   if self == 0
    quotient, mask = 0, 1
    dividend = self
    while divisor < dividend
      divisor <<= 1
      mask    <<= 1
    end
    while mask != 0
      if dividend >= divisor
        dividend -= divisor
        quotient += mask
      end
      divisor >>= 1
      mask    >>= 1
    end
    FixedNum.new(quotient, dividend)
  end

  def real_div divisor
    return nil if divisor == 0
    return 0   if self == 0
    q = divisor == 0 ? nil : self / divisor
    r = divisor == 0 ? nil : self % divisor
    FixedNum.new(q, r)
  end

end

def test_div dividend, divisor
  test_result = dividend.my_div   divisor
  ref_result  = dividend.real_div divisor
  if test_result != ref_result
    puts "#{dividend} / #{divisor} => #{test_result} not #{ref_result}"
  end
end

1000.times do |x|
  dividend = rand(100000)
  divisor  = rand(100000)
  test_div dividend, divisor
end

exit

This is a complete program that demonstrates that the bitshifting division is exactly the same as "real" division.

The test program runs a thousand random integers as both dividends and divisors, and compares the bit-shifting division versus the built-in division.

No output means no errors.