/*******************************************************
*         File:	 DivDemo.s
*         Date:	 Oct 12, 2021
*       Author:  DSS
*    Assembler:  as under the gcc compiler                 
*      Purpose:	 Demonstrate quotient and remainder of two ints 
*******************************************************/
	
.globl main

main:
	push 	%rbp           		# keep stack aligned
	#Get operands 
	mov  	$0, %rax       		# clear AL (zero FP args in XMM registers)
	leaq 	DividendPrompt(%rip), %rdi  	# load format string to proper register
	call    printf          	# print it
	# Read dividend
	leaq 	fmt_in(%rip), %rdi  	# load format string
	leaq 	dividend(%rip), %rsi  	# set storage to address of operand
	call	scanf

	mov  	$0, %rax       		# clear AL (zero FP args in XMM registers)
	leaq 	DivisorPrompt(%rip), %rdi  	# load format string to proper register
	call    printf          	# print it
	# Read divisor 
	leaq 	fmt_in(%rip), %rdi  	# load format string
	leaq 	divisor(%rip), %rsi  	# set storage to address of operand
	call	scanf

 	# Load values from memory
	movq 	dividend(%rip), %r13	# Holders to minimize RAM access
	movq 	divisor(%rip), %r14

	# Divide
	mov	$0,%edx			# Division is a double sized dividend. High 32 -> 0
	mov	dividend(%rip),%eax	# When I loaded to %rax it had wrong value; use eax
	divq 	%r14			# Divide by value in %r14
	mov	%rax, %r11		# Store quotient
	mov 	%rdx, %r12		# Store remainder

	# Print result
        mov     $Output, %rdi		# Output string to 1st parameter
	# Two ways to load values from memory into a register
        # 1. Load directly from address
	movq	dividend(%rip),%rsi	# load dividend direct from RAM to %rsi  
	# 2. Copy address to register and load from there
	mov	$divisor,%r15		# put adrs of divisor in r15
	mov	(%r15),%rdx		# load divisor into %rdx for output 
					# quotient is already in register; just copy it
 	mov	%r11,%rcx		#   into next argument register
 	mov	%r12,%r8		# Same for remainder
        xor     %rax, %rax      	#must 0 out %rax 
	call	printf			#print it
        
done:	
	pop 	%rbp
	ret

.data
Output: 	.asciz	"%d divided by %d: Quotient: %d  Remainder:%d\n"
fmt_in: 	.string "%d"
DivisorPrompt:  .asciz	"Divisor  >" 
DividendPrompt: .asciz	"Dividend >" 
dividend:	.long 0
divisor:	.long 0