汇编语言学习系列 递归实现

假如汇编语言要实现如下C语言的功能，编译环境Ubuntu14.04（32位）。

#include<stdio.h>

int refact(int n){

    if(n == 1)

        return 1;

    else

        return n * refact(n - 1);

}



int main(){

    int a = 4;

    printf("%d\n", refact(a));

    return 0;

}

---

无论对于递归实现还是循环实现，汇编都是将转换为跳转语句实现。可以把上面的代码转换为

refact:

    if((n-1) <= 0)

    goto done;



    body-statement

        

done:

• 汇编代码refact.s

.section .data

        a: .int 4

        format: .asciz "%d\n"

.section .text

.global _start

_start:

        pushl %ebp

        movl %esp, %ebp

        subl $8, %esp #allocate storage space

        

        movl a, %edx    #get a

        movl %edx, (%esp)    #save value of a on stack

        

        call refact

        

        pushl %eax

        pushl $format

        call printf

        movl $0, (%esp)

        call exit                    

        

refact:

        pushl %ebp

        movl %esp, %ebp

        pushl %ebx

        subl $4, %esp    #allocate storage space

        

        movl 8(%ebp), %ebx    #get n

        cmpl $1, %ebx    

        jle done    #test (n-1) >= 0

        

        leal -1(%ebx), %eax    #(n-1)

        movl %eax, (%esp)　　#save (n-1) on the stack

        call refact

        imul %ebx, %eax　　#use %eax to save result 

        

done:    

        addl $4, %esp    #release space

        popl %ebx

        popl %ebp

        ret

        

• 编译

 as refact.s -o refact.o

• 链接

ld -lc -I /lib/ld-linux.so.2 refact.o -o refact

• 执行

 ./refact