/*******************************************************
*         File:  ArrayEx1.s           
*         Date:  Oct. 11, 2021
*       Author:  DSS
*     Computer:  KUNET suns
*      Execute:  ArrayEx1
*      Purpose:  to demonstrate the use of arrays as allocated on the stack. 
*		 It illustrates how components of the arrays are referenced 
*		 efficiently and demonstrates offsets via an index search
*
*		 This program will define an integer array (size 10) stored in the stack
*		 and use a for loop to read in *up to* ten values and print them out.
*
*		 It uses minimal code, optimizing several things
*******************************************************/

.global main

main:
	push 	%rbp           		# keep stack aligned
	# Make room for 10 ints on the stack
	subq	$48, %rsp		# must also remain divisible by 16
	movq	$0, %r14		# Count # elts
loop:
	# Read a value
	leaq 	prompt(%rip), %rdi  	# load format string to proper register
	call    printf          	# print it
	# Read the int
	leaq 	fmt_in(%rip), %rdi  	# load format string
	leaq 	(%rsp,%r14,4), %rsi  	# set storage to address of  elt on stack
	call	scanf			
	inc	%r14			# Counter up
	cmp	$10,%r14 		# If equal, time to exit
	jz	print

	# Did they enter ^D (eotext)? scanf returns #items read, -1 on ^D
	cmp	$1,%rax		
	je	loop			# If it was 1, go get next value
	dec	%r14

	movq	$0, %r15		# #elts is in %r14, %r15 is now counting
print:
	leaq	frmto(%rip),%rdi	# Output format
	mov	%r15,%rsi
	mov	(%rsp,%r15,4),%rdx	# Load value to print
	xor	%rax,%rax
	call	printf
	# Are we done?
	inc	%r15			# Inc counter
	cmp	%r14,%r15		# Equal to # elts?
	jl	print			# No? Print next value

done:
	addq	$48, %rsp		# Deallocate the array (not critical)
	pop	%rbp
	ret

.data

prompt:	.asciz	"enter up to ten numbers (^D quits): "
fmt_in:	.asciz	"%d"
frmto:	.asciz	"\narray[%d] = %d"