/*
	Hand-coded assemby for calculating the GCD

      int gcd(int a, int b)
      {
	while (a!=0 && b!=0)
	{
		if (a<b) b = b%a; 
		else a = a%b; 
	}
	return a+b;
      }

	a in 8(ebp), b in 12(ebp) 
*/

gcd:
	push %ebp		# create new stack frame (no local vars)
	mov %esp, %ebp
gcdloop:	
	mov 8(%ebp),%ebx	# a
	mov 12(%ebp), %ecx	# b
	cmp $0, %ebx
	je loopexit
	cmp $0, %ecx
	je loopexit
	mov $0, %edx		# prepare for division
	cmp %ebx,%ecx		# if a<b
	jle optionb
optiona:
	mov %ecx,%eax           # b = b%a
	idiv %ebx		# remainder now in %edx
	mov %edx, 12(%ebp)
	jmp gcdloop
optionb:
	mov %ebx,%eax		# a=a%b
	idiv %ecx
	mov %edx, 8(%ebp)
	jmp gcdloop
loopexit:
	mov 8(%ebp), %eax
	add 12(%ebp), %eax	# store return value in eax
	mov %ebp, %esp          # pop stack frame and return
	pop %ebp
	ret


.section	.rodata
STR1:	.string "enter two numbers: "
STR2:	.string "%d %d"
STR3:	.string "the gcd is %d\n"


.globl main

main:
	push $STR1
	call printf     # display prompt
	sub $8, %esp	# make room for a, b on stack
	leal (%esp), %eax	# prepare for scanf call
	leal 4(%esp), %ebx
	push %ebx
	push %eax
	push $STR2		
	call scanf		# scanf("%d %d",&a,&b)
	add $12,%esp		# deallocate scanf args

/*   this would print the numbers just scaned in
	push $STR2
	call printf
	add $4, %esp
*/
	      /* at this point, stack still contains a, b numbers */
	call gcd
	add $8, %esp
	push %eax
	push $STR3
	call printf
	add $8, %esp
	push $0
	call exit