LC3 N装配广场 [英] LC3 Assembly Square of N

问题描述

我正在尝试编写一个计算数字平方并将其存储在r0中的lc3汇编程序，该整数作为参数提供并位于r1中，我在调试时注意到的问题是在第一个过程中通过它最初添加2，但第二次通过它未能将另一个2添加到r0-我的代码在任何帮助下都值得赞赏

Hi I'm trying to write a lc3 assembly program which computes the square of a number and stores it in r0, the integer is given as a parameter and is located in r1, the problem i noticed while debugging is during the first pass it initially adds 2, but the second pass it fails to add another 2 to r0 - My code is below any help is appreciated

           .orig x3FF8
      ld r1,n
    ld r5,n

  square
 add r2,r1,#0

  add r5,r5,#-1
add r0,r2,#0
brzp square
brn theend

  theend


halt
 n .fill #2

 .end

我的最终代码感谢提供帮助的用户:

my final code thanks to the user who helped:

    .orig x3FF8
     ld r1,n
    ld r5,n

   square


  add r2, r2,r1

  add r5,r5,#-1

  brp square


  theend


 halt
  n .fill #4

 .end

推荐答案

如果我没有记错LC-3语法，add r2,r1,#0会执行r2 = r1 + 0，因此它实际上并没有添加到r2中，只是用r1.

If I remember LC-3 syntax correctly, add r2,r1,#0 does r2 = r1 + 0, so it was never actually adding to r2, just overwriting it with r1.

您希望在循环外中进行类似的操作以初始化r2.

You want something like that outside the loop to initialize r2.

但是在循环内部，您需要add r2, r2, r1来执行r2 = r2 + r1，即r2 += r1.

But inside the loop, you want add r2, r2, r1 which does r2 = r2 + r1, i.e. r2 += r1.

我不明白为什么循环中也有add r0,r2,#0. 如果要在r0中获得最终结果，请首先在r0中进行累加.如果那应该是总和，那么您有同样的错误.

I don't understand why you have add r0,r2,#0 inside the loop as well. If you want the final result in r0, accumulate it in r0 in the first place. Of if that was supposed to be a sum of sums, then you have the same bug.

还请注意，add r5,r5,#-1必须是最后一个，因此从其为循环分支设置条件代码标志，而不是从add r0, r0, r2或循环内需要的其他任何地方设置.

Also note that add r5,r5,#-1 needs to be last so condition code flags are set from it for the loop branch, not from add r0, r0, r2 or whatever else you need inside the loop.

也:brn theend完全没用:theend在下一行，执行继续到下一行.您不必跳过源代码中的空白！

Also: brn theend is totally useless: theend is on the next line, and execution continues to the next line on its own. You don't have to jump over whitespace in the source!

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