section .data

	.global a
	.global b
	.global c
	.global d
	.global res

.section .text
	.global operation

operation:

	# prologue
	pushl %ebp # save previous stack frame pointer
	movl %esp, %ebp # the stack frame pointer for sum function

	#operation
	movl $0, %ebx

	movb a, %al
	movw b, %bx
	movl c, %ecx
	movl d, %edx

	addw %ax, %bx
	subl %ecx, %ebx
	movl %ebx,%eax
	addl %edx, %eax

	movl $0, %edx
	movl %eax, res # copy the result to res


	# epilogue
	movl %ebp, %esp # restore the previous stack pointer ("clear" the stack)
	popl %ebp # restore the previous stack frame pointer

	ret