/*******************************************************
*         File:  AddXY_NoDef.s           
*         Date:  Oct. 24, 2021
*       Author:  DSS
*     Computer:  acad
*     Assemble:  asm AddXY_NoDef
*      Execute:  AddXY   
*      Purpose:  to demonstrate allocation of automatic (local) variables on the stack. 
*
*		 This program will declare ints x and y by allocating space for them in 
*	 	 main()'s stack frame. x and y will be read and stored directly 
*		 Their sum will be computed and  output
*		 Several registers will be aliased
*
*		 It demonstrates a downfall of using defines    
*******************************************************/

.global main

main:
	push 	%rbp           		# keep stack aligned
	# Make room for x and y on the stack
	subq	$16, %rsp		# must also remain divisible by 16

	# Read values
	leaq 	prompt(%rip), %rdi  	# load format string to proper register
	call    printf          	# print it
	# Read x and y  
	xor	%rax,%rax
	leaq 	fmt_in(%rip), %rdi  	# load format string
	movq	%rsp, %rsi
	addq	$0, %rsi
	movq	%rsp, %rdx
	addq	$4, %rdx
	call	scanf			

	# Load and sum
	# Put x location in xReg
	movq	(%rsp),%r12		# Value of x into xReg (offset is 0)
	# Put y location in xReg
	movq	4(%rsp),%r13		# Value of y into yReg (offset is 4)
	# Sum
	xor	%r14, %r14		# Clear the sum register zReg
	addq	%r12, %r14		# Add x to it
	addq	%r13, %r14		# Add y to it

	# Print
	leaq	frmto(%rip),%rdi	# Output format
	mov	%r12,%rsi
	mov	%r13,%rdx
	mov	%r14,%rcx
	xor	%rax,%rax
	call	printf

done:
	addq	$16, %rsp		# Deallocate the variables           
	pop	%rbp
	ret

.data

prompt:	.asciz	"enter x and y: "
fmt_in:	.asciz	"%d %d"
frmto:	.asciz	"%d + %d = %d\n"