x86程序集初学者:程序无法正确循环？

Question

以下程序的目标是接受来自用户输入的最多10个带符号的8字节浮点数(-100≤X≤100)并将它们存储到数组中.使用ReadFloat Irvine方法接收用户输入.如果输入该范围之外的数字,则子程序应该停止执行并通过eax返回当前数组中的值的数量.这只是用来描述程序应该做什么的一些上下文.我对此代码的问题是它在接受第一个值后没有正确循环.我进行了设置,以便检查输入数字是否在L1中高于或等于-100,然后在L2中低于或等于100.如果数字超出该范围,则子程序应停止执行,但如果它在该范围内,则应进入L3和R1.在L3和R1中,数字被放入SFPArray中的索引中,如果数组中的值少于10,则程序应无条件地跳回L1以进行进一步的迭代.R1中的JMP命令是问题所在.在输入单个数字后,当前状态的子程序将停止执行,我无法弄清楚原因.有人可以提供帮助吗？

INCLUDE    c:\irvine\irvine32.inc
INCLUDELIB c:\irvine\irvine32.lib
INCLUDELIB c:\masm32\lib\user32.lib
INCLUDELIB c:\masm32\lib\kernel32.lib


.data
theSFPArray REAL8 10 dup(?)             ;an array that can store up to 10 signed floating point numbers
tempStoreFP REAL8 ?                     ;this variable will temporarily store the FP number acquired from user input, and then push it onto the stack
lengthOfSFPArray DWORD ?                ;this variable will store the length of theSFPArray. This value will be used to determine if requestSignedFloats should stop looping.
inputLoopCounter DWORD -1               ;used to determine when the requestSignedFloats subroutine should stop accepting input.                 
prompt BYTE "Please enter a value: ",0


.CODE

main PROC

    call    requestSignedFloats
    exit

main ENDP

requestSignedFloats PROC

    finit                                 ;initializes floating point unit
    push    edx                           ;pushes the original value of edx onto the stack. This will be popped when the subroutine ends.
    mov     edx, OFFSET theSFPArray       ;moves the offset of theSFPArray into edx so that values can be placed into it.
    push    edx                           ;pushes edx onto the stack while it contains the offset of the SFPArray for later usage.   

    mov eax,100
    push eax
    fild dword ptr [esp]                  ;get the 100 from memory and throw it onto the FPU, into ST(0)
    fchs                                  ;changes the 100 in ST(0) into -100
    pop eax                  

L1: 
    mov     edx,OFFSET prompt                          
    call    WriteString                   ;displays the String within the prompt variable on the screen.          
    call    ReadFloat                     ;requests a float as input from the user and stores it at the top of the floating point stack, aka ST(0).
    fcom                                  ;compares the value in ST(1) to the value in ST(0).
    jae     L2
    pop     edx                           ;this line and the two lines below it will execute if the comparison dictates that ST(1) is below the value in ST(0). This should cause the subroutine to end.
    pop     edx                           ;a second pop of edx is necessary to restore edx to its original value since two alterations of edx were placed onto the stack at the beginning of the subroutine.
    mov     lengthOfSFPArray,LENGTHOF theSFPArray ;Moves the current number of values stored in theSFPArray into the lengthOfSFPArray variable.
    mov     eax,lengthOfSFPArray          ;Returns in eax,the number of values in the array, as specified by the requirements
    ret
L2: 
    fstp    tempStoreFP                   ;pops the user input value off of the stack temporarily so that fchs can be used to change the sign of the value in ST(0)
    fchs                                  ;changes the -100 in ST(0) into a positive 100.
    fld     tempStoreFP                   ;pushes tempStoreFP back onto the stack so that its value is now in ST(1)
    fcom    
    jbe     L3
    pop     edx                           ;this line and the two lines below it will execute if the comparison dictates that ST(1) is below the value in ST(0). This should cause the subroutine to end.
    pop     edx                           ;a second pop of edx is necessary to restore edx to its original value since two alterations of edx were placed onto the stack at the beginning of the subroutine.
    mov     lengthOfSFPArray,LENGTHOF theSFPArray ;Moves the current number of values stored in theSFPArray into the lengthOfSFPArray variable.
    mov     eax,lengthOfSFPArray          ;Returns in eax,the number of values in the array, as specified by the requirements
    ret
L3: 
    pop     edx                           ;this is done to pop the offset of theSFPArray off of the stack and back into edx since at this point edx still stores the "prompt".
    inc     inputLoopCounter              ;increments inputLoopCounter so that its value is equal to the index that the number input by the user will be stored in.
    mov     ecx,inputLoopCounter          ;uses inputLoopCounter to determine how many times the loop will execute.
R1:
    inc     edx                           ;increments edx an amount of times equivalent to the value stored in inputLoopCounter.
    loop    R1
    fstp    qword ptr [edx]               ;takes the value at the top of the stack and stores it as a REAL8 at the address specified by edx (aka its array index)
    mov     lengthOfSFPArray,LENGTHOF theSFPArray ;Moves the current number of values stored in theSFPArray into the lengthOfSFPArray variable.
    fchs                                  ;changes the 100 in ST(0) to a -100 in preparation for the next iteration of the subroutine.
    cmp     inputLoopCounter,10
    je      L4
    jmp     L1                            ;An unconditional jump to L1 that causes this subroutine to execute repeatedly. The line above this one prevents it from being an infinite loop.
L4:
    mov     eax,lengthOfSFPArray          ;Returns in eax,the number of values in the array, as specified by the requirements
    pop     edx                           ;if the program makes it to this point, the offset of the array would have been popped off of the stack, meaning the original value of edx is the only thing
                                          ;remaining on the stack, so only one pop is necessary
    ret

requestSignedFloats ENDP

Answer 1

在您的.data部分中,您可以lengthOfSFPArray像这样定义

lengthOfSFPArray DWORD ?                ;this variable will store the length of theSFPArray. This value will be used to determine if requestSignedFloats should stop looping.

这?意味着初始值未定义,因此介于0和2 ^ 32-1之间.

在L1中,您可以undefined使用

mov     eax,lengthOfSFPArray          ;Returns in eax,the number of values in the array, as specified by the requirements

因此,初始化时EAX会有undefined或者有什么价值lengthOfSFPArray.你在L2中重复一遍.

在R1设置lengthOfSFPArray与

mov     lengthOfSFPArray,LENGTHOF theSFPArray

到LENGTHOF theSFPArray,在本data节中定义为

theSFPArray REAL8 10 dup(?)

根据定义,它的元素数量为theSFPArray:LENGTHOF(theSFPArray) = 10.

之后,将值10与值10进行比较,它总是TRUE:

cmp     lengthOfSFPArray,10
je      L4                     ; ALWAYS jump to L4
jmp     L1                     ; NEVER reached

L4:是你的退出标签,所以整个过程只执行一次.