装配找到两个值的最大值

Question

我试图找到两个值之间的最大值

_FindMax:
    push ebp
    mov ebp, esp

    mov eax, dword [ebp+12]  ; get fist argument
    mov ebx, dword [ebp+8]   ; get second argument


    cmp eax, ebx
    jl LESS       ; if eax less to LESS

    LESS:
    mov eax, ebx ; ebx is greate and return it

    mov esp, ebp
    pop ebp

    ret

但问题是 LESS: 标签总是在执行。例如，如果参数相等，则 LESS: 标签正在执行。为什么？？

Answer 1

A really efficient way to achieve this would be (assuming that you have at least a P6 family processor):

_FindMax:
    mov eax, dword [esp+8]       /* get first argument */
    mov ebx, dword [esp+4]       /* get second argument */
    cmp eax, ebx                 /* compare EAX to EBX */
    cmovl eax, ebx               /* MOV EBX to EAX if EBX > EAX */
    ret

This code omits the stack frame (EBP) and uses an inline MOV operation to do the comparison. Nevertheless, the return value is still in EAX.