Ruby 中通过进位左旋转

Question

我正在尝试在 Ruby 中实现 SHA1，为此我需要通过进位执行左旋转。我编写的代码似乎可以工作 1 轮，但超过 1 轮后它就无法通过我的测试，有人知道为什么吗？

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

我首先检查了 Wikipedia 以确保我理解该操作。看起来你好像失去了你的随身物品。另外，我添加了测试类以确保我得到正确的答案。我不确定您是否想保留进位，因此我注释掉了代码以截断结果。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

您使用什么来确定尺寸？例如，如果您尝试进行 4 位旋转，并且将大小设置为 4，则first_bit 计算将获取第 5 位：

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

---

因此索引正常。但在内循环中，您从 self 获取first_bit，而不是temp。所以这只会在第一次时有效。

Answer 3

我曾经在Ruby中实现了 SHA-256 （使用右旋转）并最终使用这段代码：

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......但它有效:)