Question

我有一个我用ADA编写的Karatsuba算法实现。

   procedure Karatsuba (Factor_1, Factor_2 : in Number; Product : out Number) is
      m : Integer;
      m2 : Integer;
      low1 : Number := (0,1);
      high1 : Number := (0,1);
      low2 : Number := (0,1);
      high2 : Number := (0,1);
      z0 : Index;
      z1 : Index;
      z2 : Index;
      x : Integer;
      y : Integer;
      hc1 : Index;
      hc2 : Index;
   begin
      low1 := (others => 0);
      high1 := (others => 0);
      low2 := (others => 0);
      high2 := (others => 0);  
      if Factor_1'Length = 1 or Factor_2'Length = 1 then
         Standard(Factor_1, Factor_2,Product);
      end if;
      -- calculates the size of the numbers
      m := Integer'Max(Factor_1'Length, Factor_2'Length);
      m2 := m / 2;
      -- split the digit sequences about the middle
      for Factor_1_Index in Factor_1'Range loop
         x := x + 1;
         if x <= m2 then
            low1(Factor_1_Index) := Factor_1(Factor_1_Index);
         else
            high1(hc1) := Factor_1(Factor_1_Index);
            hc1 := hc1 + 1;
         end if;
      end loop;
      for Factor_2_Index in Factor_2'Range loop
         y := y + 1;
         if y <= m2 then
            low2(Factor_2_Index) := Factor_2(Factor_2_Index);
         else
            high2(hc2) := Factor_2(Factor_2_Index);
            hc2 := hc2 + 1;
         end if;
      end loop;
      -- 3 calls made to numbers approximately half the size
      z0 := Karatsuba(low1, low2, Product);
      z1 := Karatsuba((low1 + high1), (low2 + high2), Product);
      z2 := Karatsuba(high1, high2, Product);
      Product := (z2*10**(2*m2))+((z1-z2-z0)*10**(m2))+(z0);
   end Karatsuba;

在“结束Karatsuba”行之前的最后4行，我得到错误“期望类型'索引'定义为......”。我收到的错误分别是

expected type "Index" defined at ....
found package or procedure name
there is no applicable operator "+" for type "Number" defined at ......

这是我分配了一些变量的另一个类：

package ITI8590.Natural_Number_Multiplication is

   type Digit  is range 0 .. 1;
   type Index  is new Positive;
   type Number is array (Index range <>) of Digit;

   for Digit'Size use 1;

   procedure Standard(Factor_1, Factor_2 : in Number; Product : out Number);
   procedure Karatsuba(Factor_1, Factor_2 : in Number; Product : out Number);

end ITI8590.Natural_Number_Multiplication;

为什么我会收到此错误？我无法解决它，我陷入其中。你能帮帮我吗？

谢谢，

Answer 1

Karatsuba是一个程序，所以最后而不是

  z0 := Karatsuba(low1, low2, Product);
  z1 := Karatsuba((low1 + high1), (low2 + high2), Product);
  z2 := Karatsuba(high1, high2, Product);

应该阅读

  Karatsuba(low1, low2, z0);
  Karatsuba((low1 + high1), (low2 + high2), z1);
  Karatsuba(high1, high2, z2);

要求您将z0，z1，z2声明为Number而不是Index。请注意，Product是过程的out参数，因此您获得的所有代码都是使用中间结果覆盖两次（3次，计算上面对Standard的调用）。

但是你遇到了问题：编译器说

yusuf.ada:25:12: unconstrained subtype not allowed (need initialization)
yusuf.ada:25:12: provide initial value or explicit array bounds

正在调用与您声明low1等方式相关的内容：

  low1 : Number := (0,1);
  high1 : Number := (0,1);
  low2 : Number := (0,1);
  high2 : Number := (0,1);

这种方法的问题在于您现在已经约束了变量的边界：low1被修复为具有2个元素（设置为您随后覆盖的值），并且无法展开。我不知道该算法应该如何工作，但这似乎不太合适;首先，如果输入超过2位，会发生什么？

可能有效的一种方法是使用输入参数中的位数：

Max_Digits : constant Positive := Factor_1’Length + Factor_2’length;
pragma Assert (Product’Length >= Max_Digits, “possible overflow”);
low1 : Number (1 .. Max_Digits) := (others => 0);

等

而且，正如ajb所评论的那样，您需要在+ s和{{之间定义运算符-，*，**，Number 1}}根据需要，特别是在过程的最后一行中的表达式Integers中。

期望的类型＆＃34; ...＆＃34;在Ada中定义.......错误

1 个答案: