; intfunct_64.asm  this is a main and a function in one file
;                  call integer function  long int sum(long int x, long int y) 
; compile:	nasm -f elf64 -l intfunct_64.lst intfunct_64.asm 
; link:		gcc -m64 -o intfunct_64 intfunct_64.o
; run:		./intfunct_64 > intfunct_64.out
; view:         cat intfunct_64.out
; result:	5 = sum(2,3)

	extern	printf
	section .data
x:	dq	2
y:	dq	3
fmt:	db	"%ld = sum(%ld,%ld)",10,0

	section .bss
z:	resq	1
	
	section .text
	global	main
main:	push	rbp		; set up stack

	mov	rdi, [x]	; pass arguments for sum
	mov	rsi, [y]
	call	sum		; coded below
	mov	[z],rax		; save result from sum

	mov	rdi, fmt	; print
	mov	rsi, [z]
	mov	rdx, [x]	; yes, rdx comes before rcx
	mov	rcx, [y]
	mov	rax, 0		; no float or double
	call	printf

	pop	rbp		; restore stack
	mov	rax,0
	ret
; end main

sum:	; function long int sum(long int x, long int y)
	; so simple, do not need to save anything

	mov	rax,rdi		; get argument x
	add	rax,rsi		; add argument y, x+y result in rax
	ret			; return value in rax
; end of function sum
; end intfunct_64.asm