.file   "sum64.s"
        .text
        .globl  sum

sum:                        # int sum(const int *a, int n)
                            #     a == %rdi, n == %rsi
        pushq   %rbp        # save frame pointer in stack
        movq    %rsp, %rbp  # new FP points to old FP in stack
        
        movl    $0, %eax    # sum := 0
L0:                         # loop
        cmpl    $0, %ecx      # compare n with 0 
        jle     L1            # if result <= 0 goto L1  (le = less or equal)
        addl    (%rdi), %eax  # sum += *a
        addq    $4, %rdi      # a += 4
        subl    $1, %esi      # n -= 1
        jmp     L0            # goto L0
L1:
        movq    %rbp, %rsp  # SP := FP
        popq    %rbp        # restore old FP
        ret