Question

我正在尝试在Ruby中实现SHA1，为了做到这一点，我需要通过carry执行左旋转。我写的代码似乎可以用于1次旋转，但是除了我的测试失败之外，任何人都知道为什么？

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

    count.times do
      first_bit = (self & 2 ** size)[size]
      temp = temp << 1
      temp = temp ^ first_bit
      temp = temp ^ (2 ** (size + 1))
    end

    return temp
  end
end

Answer 1

我首先检查Wikipedia以确保我了解操作。看起来你好像丢失了随身携带物。另外，我添加了测试类，以确保我得到了正确的答案。我不确定你是否想要保留所携带的位，所以我注释掉了截断结果的代码。希望这有帮助！

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

Answer 2

你在size使用了什么？例如，如果您尝试进行4位旋转，并将size设置为4，则first_bit计算得到第5位：

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

所以索引是好的。但是在内循环中，你从self获得first_bit而不是temp。所以这只会在第一次通过。

Answer 3

我曾经实现SHA-256 in Ruby（使用右旋转）并最终使用了此代码：

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

您可以将其修改为左旋转：

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

虽然很难理解......但是有效：）

通过Ruby中的left进行左旋转

3 个答案: