将 C 代码转换为 MIPS - 迭代阶乘函数

Question

我对编程还很陌生，刚接触几个月，只是在摆弄一些汇编代码。我运行我的 MIPS 代码有问题，在打印每个变量的值后我将问题缩小到我的循环。它只打印 1 作为任何整数输入的结果。本质上我正在尝试转换它：

int fac(int k) {
    int i, f = 1;
    for (i = 1; i <= k; i++) {
        f = f * i;
    }
    return f;
}

为此：

fac:
    move $t4, $t0 #$t0 is the input from the user and $t4 is k in the C code
    li $t1, 1 #$t1 is f in the C code, initialising it to 1
    li $t2, 1 #$t2 is i in the C code, declaring it as 1
    loop:
    ble $t2, $t4, end_loop #i<=k, end the loop
    mul $t1, $t1, $t2 #f=f*i
    addi $t2, $t2, 1
    j loop
    end_loop:

我通过放入一堆打印语句来测试代码，并且能够获得 $t4 和 $t0 作为输入，但 $t1 和 $t2 在循环后仍保持为 1。我必须跳入循环吗？

Answer 1

ble $t2, $t4, end_loop #i<=k, end the loop

不，C for 语句的第二部分是您要继续循环而不是结束循环的条件。

你在这里所做的甚至没有进入循环体，这就是为什么$t1和$t2保持与你相同的值将它们初始化为。

您可能想使用 bgt 而不是 ble。

Answer 2

如果 i<=k，你的 ble $t2, $t4, end_loop #i<=k, end the loop 循环条件将结束循环，但只要这个条件满足，你就想运行它。您的循环实现甚至没有进入大于 1 的阶乘输入的循环。

编辑： 正如下面代码的评论中所说，我已经实现了一个 do {...} while (); 循环，这不是 OP 所要求的。但是代码会起作用。在描边文本下面是真正的答案（for 循环实现）。

~~删除 end_loop: 标签并跳转到 loop: 标签，将 ble 作为最后一条语句：~~

fac: move $t4, $t0 #$t0 is the input from the user and $t4 is k in the C code li $t1, 1 #$t1 is f in the C code, initialising it to 1 li $t2, 1 #$t2 is i in the C code, declaring it as 1 loop: mul $t1, $t1, $t2 #f=f*i addi $t2, $t2, 1 ble $t2, $t4, loop #i<=k, loop goes on if not this doesn't jump

要实现您要求的 for 循环，您需要更改 ble (<=):

ble $t2, $t4, end_loop #i<=k, end the loop

至bgt (>):

bgt $t2, $t4, end_loop #i>k, end the loop

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