Left rotate through carry in Ruby

I'm trying to implement SHA1 in Ruby and in order to do so I need to preform a left rotate through carry. The code I've written seems to work for 1 rotation, but any more than that it fails my tests, anybody know why?

class Integer
  def rotate_left(count, size)
    temp = self

    count.times do
      first_bit = (self & 2 开发者_运维问答** size)[size]
      temp = temp << 1
      temp = temp ^ first_bit
      temp = temp ^ (2 ** (size + 1))
    end

    return temp
  end
end

I checked Wikipedia first to make sure I understood the operation. It looks as if you were losing your carry's. Also, I added the test class to make sure I was getting the right answers. I wasn't sure if you wanted to preserve the carried bits or not so I commented out the code to truncate the result. Hope this helps!

class Integer
    def rotate_left(count, size)
        temp = self
        carry = 0

        count.times do
            temp = temp << 1
            temp = temp | carry
            carry = (temp >> size) & 1
        end

        return temp # & (( 1 << size ) - 1)
    end

end

if __FILE__ == $0 then

    require 'test/unit'

    class TestRotateLeft < Test::Unit::TestCase
        def test_no_rotation
            result = 5.rotate_left(0,4)
            answer = result & 15
            carry = ( result & 16 ) >> 4
            assert_equal 5, result
            assert_equal 0, carry
        end

        def test_one_rotation
            result = 5.rotate_left(1,4)
            answer = result & 15
            carry = ( result & 16 ) >> 4
            assert_equal 10, answer
            assert_equal 0, carry
        end

        def test_first_carry
            result = 5.rotate_left(2,4)
            answer = result & 15
            carry = ( result & 16 ) >> 4
            assert_equal 4, answer
            assert_equal 1, carry
        end

        def test_shift_from_carry
            result = 5.rotate_left(3,4)
            answer = result & 15
            carry = ( result & 16 ) >> 4
            assert_equal 9, answer
            assert_equal 0, carry
        end

        def test_second_carry
            result = 5.rotate_left(4,4)
            answer = result & 15
            carry = ( result & 16 ) >> 4
            assert_equal 2, answer
            assert_equal 1, carry
        end

        def test_full_rotation
            result = 5.rotate_left(5,4)
            answer = result & 15
            carry = ( result & 16 ) >> 4
            assert_equal 5, answer
            assert_equal 0, carry
        end

    end

end

what are you using for size? If you are trying to do a 4 bit rotation for example, and you set size to 4, then the first_bit calculation is getting the 5th bit:

 2**4 => 16
 16.to_s(2) => "10000"   

So the indexing is Ok. But in the inner loop, you are getting first_bit from self instead of temp. So this will only work the 1st time through.

I once implemented SHA-256 in Ruby (which is using right rotate) and finally used this code:

class Integer
  def rotate(n=1)
    self >> n | self << (32 - n)
  end
end

You can modify it for left rotate:

class Integer
  def lotate(n=1)
    self << n | self >> (32 - n)
  end
end

Although it's very hard to understand... it works :)