!  add.s
!  compute the following: result = (a+b)-(c+d)

	.data                       ! variables            

a:	.word 20                    ! initialize a to 20
b:	.word 4                     ! initialize b to 4
c:	.word 2                     ! initialize c to 2
d:	.word 15                    ! initialize d to 15
result:	.word 0                     ! initialize result to 0

	.text
start:
	set    a, %r2               ! &a --> %r2
	ld     [%r2], %r2           !  a --> %r2
	set    b, %r3               ! &b --> %r3
	ld     [%r3], %r3           !  b --> %r3
	set    c, %r4               ! &c --> %r4
	ld     [%r4], %r4           !  c --> %r4
	set    d, %r5               ! &d --> %r5
	ld     [%r5], %r5           !  d --> %r5

	add    %r4, %r5, %r4        ! c+d --> %r4
	add    %r2, %r3, %r7        ! a+b --> %r7
        sub    %r7, %r4, %r7        ! %r7-(c+d) --> %r7

	set    result, %r2          ! &result --> %r2
        st     %r7, [%r2]           ! %r7 --> result

end:	ta     0