Question

我做了一个nasm程序，计算一定大小的两个向量之间的eucledian距离。这个nasm函数是从C文件中调用的，它获取函数的结果。我已经测试了，它的工作原理，返回的值是正确的，我可以用任何问题打印出来。我的问题是当我尝试在nasm文件中打印结果时。这是nasm代码：

extern printf

%macro print_dist2 1

section .data
.str db %1,0                    ; %1 is macro call first actual parameter
section .text

push dword [dist]
push dword .str
push dword fmt2
call printf
add esp, 12                     ; pop stack 3 * 4 bytes

%endmacro




section .data           

dist: dd 258                    

fmt2: db "%s, dist: %g",10,0     ; format string for printf

section .bss            


section .text           

global distanza

x   equ 8
y   equ 12
dim equ 16
ris equ 20


distanza:
    ; ------------------------------------------------------------
    ; Function entrance sequence
    ; ------------------------------------------------------------
    push    ebp     
    mov ebp, esp    
    push    ebx     
    push    esi
    push    edi
    ; ------------------------------------------------------------
    ; read the parameters from the current stack frame
    ; ------------------------------------------------------------



    mov eax, [ebp+x]    ; address of x
    mov ebx, [ebp+y]    ; address of y
    mov ecx, [ebp+dim]  ; size of the vectors (it's the same)
.
.
. omitted calculations.
.

    sqrtss  xmm1, xmm1
    movss   [dist], xmm1    ; move the result to dist
    fld     dword [dist]    ; mov in st0, that will be used by the C file 

    print_dist2 "distanza"

    ; ------------------------------------------------------------
    ; Function exit sequence
    ; ------------------------------------------------------------

    pop edi     
    pop esi
    pop ebx
    mov esp, ebp    
    pop ebp     
    ret

这是C档案：

 float a[] = {6.1f, 9.5f, 12.6f};
 float b[] = {25.1f, 34.1f, 9.6f};
 dim = 3;

 float dist = distanza(a, b, dim);

 printf("d(x,y) = %f\n", dist);

这是输出：

distanza, dist: 5.46877e-315
d(x,y) = 31.227551

C，代码打印正确的值，nasm没有。如果我更改了nasm代码的格式字符串：

fmt2: db "%s, dist: %f",10,0

我使用％f而不是％g，nasm输出就是这个：

distanza, dist: 0.000000

我不知道我的代码有什么问题，为什么它没有打印正确的值？

Answer 1

您的dist是一个32位浮点数，但printf需要一个双64位浮点数。你必须改变它：

%macro print_dist2 1

section .data
.str db %1,0                    ; %1 is macro call first actual parameter
section .text

sub esp, 8                      ; Space for a 64-bit double floating point number
fld dword [dist]                ; Load a 32-bit single floating point number
fstp qword [esp]                ; Store it as 64-bit floating point number
push dword .str
push dword fmt2
call printf
add esp, 16                     ; pop stack 4 * 4 bytes

%endmacro

Nasm，没有打印正确的值

1 个答案: