sub6.asm

来自「关于linux环境下的nasm代码的生成和使用」· 汇编 代码 · 共 53 行

;
; file: sub6.asm
; Subprogram to C interfacing example

; subroutine calc_sum
; finds the sum of the integers 1 through n
; Parameters:
;   n    - what to sum up to (at [ebp + 8])
; Return value:
;   value of sum
; pseudo C code:
; int calc_sum( int n )
; {
;   int i, sum = 0;
;   for( i=1; i <= n; i++ )
;     sum += i;
;   return sum;
; }
;
; To assemble:
; DJGPP:   nasm -f coff sub6.asm
; Borland: nasm -f obj  sub6.asm

segment .text
        global  calc_sum
;
; local variable:
;   sum at [ebp-4]
calc_sum:
        enter   4,0               ; make room for sum on stack

        mov     dword [ebp-4],0   ; sum = 0
        mov     ecx, 1            ; ecx is i in pseudocode
for_loop:
        cmp     ecx, [ebp+8]      ; cmp i and n
        jnle    end_for           ; if not i <= n, quit

        add     [ebp-4], ecx      ; sum += i
        inc     ecx
        jmp     short for_loop

end_for:
        mov     eax, [ebp-4]      ; eax = sum

        leave
        ret