在隔离NASM剩余计划 [英] Isolating remainder in nasm program

问题描述

我目前正在写在x86 Linux的一个NASM计划，我想执行分割的第一个命令行参数（一年），由第一闰年检查的计算。我要检查，如果余数为0或没有，但我有如何做到这一点挣扎。我知道在div命令存储在某个寄存器中的答案，一个在另一个余但现在我只是使用测试。这里的code

I'm currently writing a NASM program on x86 Linux and I'm trying to perform a calculation that divides the first command line arg (a year) by the first leap year check. I want to check if the remainder is 0 or not but I'm struggling with how to do that. I know the div command stores the answer in a certain register and a remainder in another but right now I'm just using test. Here's the code

        global  main
        extern  puts
        extern  printf
        extern  atoi

        section  .text

main:
        sub     rsp, 8
        cmp     rdi, 2
        jne     error1              ; jump if aguments != 1
        mov     rdi, [rsi+8]
        call    atoi
        test    rdi, fourTest
        jnz     notLeapYear
        jmp     done
testTwo:
        jmp     done

notLeapYear:
        mov     edi, nLeap
        call    puts
        jmp     done
error1:
        mov     edi, badArgs
        call    puts
        jmp     done  

done:
        add     rsp, 8
        ret

badArgs:
        db      "Requires exactly one argument", 5, 0

nLeap:
        db      "Not a leap year", 5, 0

        section  .data
fourTest:      dq       4
hundTest:      dq       100
fHundTest:     dq       400

我相信我需要测试RDI，fourTest改为采用div，但不知道如何隔离剩余，并决定，如果我要跳到下一个测试或者我是否应该跳到是不是闰年。

I believe I need to change the test rdi, fourTest to using div but don't know how to isolate the remainder and determine if I should jump to the next test or if I should jump to is not a leap year.

推荐答案

首先，返回值从函数进入 EAX ，所以这其中与atoi 结果将是。然后使用 DIV 是这样的：

First, return values from functions go into eax, so that's where the atoi result will be. Then use div like this:

xor edx,edx
div 4

现在分工的结果将是 EAX ，其余的将在 EDX 。

Now the result of the division will be in eax, and the remainder will be in edx.

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