在NASM Assembly中递归添加数组中的所有元素

Still on my way to learn recursion in NASM Assembly, 32-bit Ubuntu, I am now trying to add all the elements in an array recursively. The array's elements are all 4-bytes each.

我仍然在学习32位Ubuntu的NASM程序集中的递归,我现在试图以递归方式添加数组中的所有元素。数组的元素都是4字节。

I came up with a solution that seems to work.

我想出了一个似乎有用的解决方案。

Basically, to add the elements in an array, I somehow need to count them, right? So I have ESI as my counter. However, this register needs to be set to 0 at the beginning of the function - but I don't think there is any way I can tell whether the current function call is the first one, or the second or third... So to fix this, I have two functions: the initial call, and the recursive call. The first one sets ESI to 0 and then calls the recursive call. The elements are all added to EAX, which is also set to 0 in the initial call..

基本上,要在数组中添加元素,我需要计算它们,对吧?所以我有ESI作为我的柜台。但是,这个寄存器需要在函数开头设置为0 - 但我不认为有任何方法可以判断当前函数调用是第一个,还是第二个或第三个......所以解决这个问题,我有两个函数:初始调用和递归调用。第一个将ESI设置为0,然后调用递归调用。这些元素都添加到EAX中,在初始调用中也设置为0。

But I'm concerned with it because it is somewhat different from two recursive functions I've done before:

但是我很担心它,因为它与我以前做过的两个递归函数有些不同:

Understanding recursive factorial function in NASM Assembly

了解NASM程序集中的递归因子函数

NASM Assembly recursive fibonacci

NASM大会递归斐波那契

Because, first of all, I'm using two functions, one for the start, and another for the actual recursive part. Also, I am using a counter, which feels awfully a lot like an iterative solution.

因为,首先,我使用两个函数,一个用于开始,另一个用于实际的递归部分。此外,我正在使用一个计数器,这非常像迭代解决方案。

So my questions are: is there a solution that resembles better the two recursive functions I posted above? Can my current solution be considered recursive?

所以我的问题是:是否有一个类似于我上面发布的两个递归函数的解决方案?我当前的解决方案可以被认为是递归的吗?

; --------------------------------------------------------------------------
; Recursive function that adds all the elements in an array into EAX.
; The array's elements are 4-bytes each.
; --------------------------------------------------------------------------

SECTION .data
    array:  dd  1,5,3,7,4,8,5,2
    size:   equ $-array

SECTION .text
    global  main
    main:

    ; ------------------------------------------------------------------
    ; * Main
    ; ------------------------------------------------------------------
    call    addVector
    breakpoint:     ; Used for GDB to inspect the result later

    ; ------------------------------------------------------------------
    ; * Exit
    ; ------------------------------------------------------------------
    mov     EAX,0
    int     0x80

    ; ------------------------------------------------------------------
    ; * Initial function call, before doing the recursive calls
    ;   Sets ESI to 0, which will be used to count the array's elements
    ;   Also sets EAX to 0, for storing the result
    ; ------------------------------------------------------------------
    addVector:
    push    ESI
    mov     ESI,0
    mov     EAX,0
    call    recursiveCall
    pop     ESI
    ret

    ; ------------------------------------------------------------------
    ; * Recursive part of the function
    ;   Adds to EAX to current element, and increases the ESI counter by
    ;   4 (because the array's elements are 4-bytes each).
    ;   If the counter happens to be >= the array's size, stop.
    ; ------------------------------------------------------------------
    recursiveCall:
    cmp     ESI,size
    jge     endRecursiveCall
    add     EAX,[array + ESI]
    add     ESI,4
    call    recursiveCall
    endRecursiveCall:
    ret

1 个解决方案

#1

First, your definition of size is wrong, your way will give you the total bytes of the array; this is not what you want. Your array is made of DWORDS, you want to know the total elements, so we divide by 4 (The size of a DWORD):

首先,你的大小定义是错误的,你的方式将给你数组的总字节数;这不是你想要的。你的数组由DWORDS组成,你想知道总元素,所以我们除以4(DWORD的大小):

size:   equ ($-array) / 4

Two ways of doing this, start from the end of the array or the beginning:

两种方法,从数组的末尾或开头开始:

From end:

array:  dd  1,5,3,7,4,8,5,2
size:   equ ($-array) / 4

SECTION .text
global  main
main:

    xor     eax, eax                        ; clear out eax
    mov     esi, size - 1                   ; set our index to array end
    call    recursiveCall

    push    eax
    push    fmtint
    call    printf
    add     esp, 4 * 2

.exit:
    call    exit

recursiveCall:
    add     EAX, dword[array + 4 * ESI]
    dec     ESI
    js      .endRecursiveCall
    call    recursiveCall

.endRecursiveCall:
    ret

From start:

SECTION .text
global  main
main:

    xor     eax, eax                        ; clear out eax
    xor     esi, esi                        ; set out index to start of array
    call    recursiveCall

    push    eax
    push    fmtint
    call    printf
    add     esp, 4 * 2

.exit:
    call    exit

recursiveCall:
    add     EAX, dword[array + 4 * ESI]
    inc     esi
    cmp     esi, size - 1
    jg      .endRecursiveCall
    call    recursiveCall

.endRecursiveCall:
    ret

#1