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
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