Question

当在程序中输入数字4时，我收到一个回答，说阶乘是268501056。显然，这是不正确的。我不太确定我的错误在哪里，我非常感谢您的帮助。

.data

    prompt: .asciiz "Enter a number to find the factorial: "
    output: .ascii "\n The factorial is "
    number: .word   0
    answer: .word   0

.text

.globl main
main:

        li $v0, 4   #get number from the user to factorial
        la $a0, prompt
        syscall

        li $v0, 5   #value stored in $v0
        syscall

        sw $v0, number  #number user entered is stored in variable number

        lw $a0, number  #number stored in a0
        jal factorial   #calling function
        sw $v0, answer  #value from factorial returned here

        li $v0,4    #display output
        la $a0, output
        syscall

        li $v0,1    #display value
        la $a0, answer
        syscall

        li $v0, 10  #end
        syscall


factorial:
        addi $sp, $sp ,-8   #allocate space in stack to store words
        sw   $ra, 0($sp)    #storing return address to first value in stack
        sw   $s0, 4($sp)    #store variable in stack

        #BASE CASE      
        li $v0, 1
        beq $a0, $0, done   #if input is equal to 0 return 1 and go to done

        #factorial(num-1)
        add $s0, $a0, $0        #put value into s0
        addi $a0, $a0,-1    #subtract 1 from argument
        jal factorial       #recursive

        mul $v0, $s0, $v0   #multiply values when the function is being popped off the stack

done:
        lw $ra, 0($sp)      #restoring values of return address
        lw $s0, 4($sp)      #loading variable back from register to the stack
        addi $sp, $sp, 8    #restore stack

        jr $ra          #return value from function

Answer 1

执行此操作时：

la $a0, answer

您正在将answer的地址加载到$ a0中，该值在我的模拟器上为0x10010040 = 268501056。之后，您需要lw $a0, 0($a0)或类似名称才能真正从该存储位置获得答案。

MIPS阶乘计算器返回的长号也许是寄存器号？

1 个答案: