Question

首先，我要感谢任何回复此帖的人，非常感谢您的帮助！

我正在尝试计算作为命令行参数传递给我的程序的一组浮点数的标准偏差。首先，我将每个参数字符串存储在temp变量中，然后使用sscanf()将它们解析为浮点数。我的第一个问题是第一个问题（当我说第一个时，我说的是我的程序名称之后的那个...实际上是第二个）命令行参数没有得到解析。在我用来计算数字平均值的循环中，我尝试在将其解析为浮点数后立即打印出每个参数。除了第一个之外，它总是打印所有这些。第一个始终打印为-nan。此外，变量std_dev也会打印为-nan，即使我从不修改它。这让我很困惑。我究竟做错了什么？

以下是代码：

EXTERN printf
EXTERN sscanf 
GLOBAL main

SEGMENT .data
form0:      DB "The standard deviation is: %d", 10, 0
form1:      DB "The standard deviation is: %f", 10, 0 
fpform:     DB "%f", 0  
avg:        DD 0.0 
std_dev:    DD 0.0   
temp:       DD 0.0 

debugform:  DB "temp=%f, std_dev=%f, avg=%f", 10, 0 

SEGMENT .text 
main:
        push    ebp                         ; compose stack frame 
        mov     ebp, esp
        push    ebx
        push    ecx

        mov     ebx, [ebp + 8]              ; ebx = # of params
        mov     ecx, [ebp + 12]             ; ecx = &param_table 
        cmp     ebx, dword 1                ; no params passed? 
        je      .end_0                      ; YES - print 0 
                                            ; NO - compute and print std_dev 
        finit                               ; initialize fpu 
        fldz                                ; initialize fpu registers with 0's 
        fldz
        fldz
        fldz
        fldz
        fldz
        fldz
        fldz

        call    findStdDev                  ; find the standard deviation of the numbers passed as command line params
        call    debugPrint
        pushad                              ; preserve all registers before making system call
        fld     dword [avg]                 ; load standard deviation into fpu
        sub     esp, 8                      ; reserve space for a qword in the stack
        fstp    qword [esp]                 ; load the 64-bit representation of std_dev into stack
        push    form1                       ; pass format string
        call    printf                      ; print out the standard deviation
        add     esp, 12 
        popad 

        jmp     .end                        ; 
        pop     ebp 
        ret 
.end_0:                                     ; if no parameters are passed, print std_dev = 0
        push    dword 0 
        push    form0
        call    printf
        add     esp, 8
.end: 
        pop     ecx
        pop     ebx
        pop     ebp                         ; restore used register and return from program 
        ret 

;-----------------------------------------------------------------------------------
findStdDev:                                 ; assumes ebx = # params, ecx = &param_table 
        push    edi                         ; save used regs 
        push    esi                         
        xor     esi, esi                    ; clear esi as a precaution 
        mov     esi, dword 1                ; loop counter for loop to find average of numbers  
.find_avg:  
        cmp     esi, ebx                    ; esi == number of params?
        je      ._break                     ; YES - break 
        pushad                              ; preserve registers before calling a C function
        push    temp                        ; temp storage for string representation of input nums
        push    fpform                      ; format string 
        push    dword [ecx + esi*4]         ; current command line param
        call    sscanf                      ; parse string to f.p. 
        add     esp, 12 
        popad 

        call    debugPrint                  ; should leave the CPU and FPU registers how they were before the call

        fld     dword [temp]                ; st0 = temp ; st1 = sum 
        faddp   st1, st0                    ; st0 = sum + temp
        ;call   debugPrint                  ; should leave the CPU and FPU registers how they were before the call
        inc     esi                         ; move to next command line param
        jmp     .find_avg

._break:
        mov     [temp], ebx                 ; temp = num of params
        sub     [temp], dword 1
        fld     dword [temp]                ; st0 = #params; st1 = sum of params
        fdivp   st1, st0                    ; st0 = (sum of params)/(#params)
        fstp    dword [avg]                 ; set avg; clear st0 

        pop     esi 
        pop     edi 
        ret 

;----------------------------------------------------------------------------------------       
debugPrint:

        pushfd 
        pushad
        sub     esp, 24
        fld     dword [avg]
        fld     dword [std_dev]
        fld     dword [temp]
        fstp    qword [esp]
        fstp    qword [esp+8]
        fstp    qword [esp+16]
        push    debugform
        call    printf
        add     esp, 28
        popad
        popfd
        ret

再次感谢！

[编辑：我还没有完成实际计算标准偏差。我所拥有的只是计算平均值的循环。]

在使用FPU Nasm x86 Assembly进行计算时获得-nan

0 个答案: