The goal
of this URM is to calculate the function: i
+ (2*j) + k and place the result in R4, where for example i = 2, j = 3 and k = 7. So the function
is now 2 + (2*3) + 7
URM
Program:
Z (4)
- J (3, 4,
6)
- S (1)
- S (2)
- S (4)
- J (1, 1,
1)
- J (2, 4,
10)
- S (1)
- S (4)
- J (1, 1,
6)
- J (1, 3,
14)
- S (3)
- S (4)
- J (1, 1,
10)
The
following points are observation about the above program.
- The
program uses registers R1, R2, R3 and R4
- If r3
= r4, the first instruction involves a jump to instruction 6
- If r2
= r4, the third instruction involves a jump to instruction 10
- If r1
= r3, the fifth instruction involves a jump to instruction 14
- The
instructions 5 involves jumping back to the first instruction if r1
= r1 and so, as this is always true, the effect of this instruction
is the unconditional jump “go to instruction number 1”. This also applies for
instructions 9 and 13.
- The
overall effect of the first and third, the fourth and sixth and the seventh and
tenth instructions is that the program includes 3 ‘do while r3 ≠ r4,
r2 ≠ r4 and r1 ≠ r3’ loops.
Illustration
of URM transaction:
Instructions
|
R1
|
R2
|
R3
|
R4
|
|
2
|
3
|
7
|
0
|
1
|
2
|
3
|
7
|
0
|
2
|
3
|
3
|
7
|
0
|
3
|
3
|
4
|
7
|
0
|
4
|
3
|
4
|
7
|
1
|
5
|
3
|
4
|
7
|
1
|
1
|
3
|
4
|
7
|
1
|
2
|
4
|
4
|
7
|
1
|
3
|
4
|
5
|
7
|
1
|
4
|
4
|
5
|
7
|
2
|
5
|
4
|
5
|
7
|
2
|
1
|
4
|
5
|
7
|
2
|
2
|
5
|
5
|
7
|
2
|
3
|
5
|
6
|
7
|
2
|
4
|
5
|
6
|
7
|
3
|
5
|
5
|
6
|
7
|
3
|
1
|
5
|
6
|
7
|
3
|
2
|
6
|
6
|
7
|
3
|
3
|
6
|
7
|
7
|
3
|
4
|
6
|
7
|
7
|
4
|
5
|
6
|
7
|
7
|
4
|
1
|
6
|
7
|
7
|
4
|
2
|
7
|
7
|
7
|
4
|
3
|
7
|
8
|
7
|
4
|
4
|
7
|
8
|
7
|
5
|
5
|
7
|
8
|
7
|
5
|
1
|
7
|
8
|
7
|
5
|
2
|
8
|
8
|
7
|
5
|
3
|
8
|
9
|
7
|
5
|
4
|
8
|
9
|
7
|
6
|
5
|
8
|
9
|
7
|
6
|
1
|
8
|
9
|
7
|
6
|
2
|
9
|
9
|
7
|
6
|
3
|
9
|
10
|
7
|
6
|
4
|
9
|
10
|
7
|
7
|
5
|
9
|
10
|
7
|
7
|
6
|
9
|
10
|
7
|
7
|
7
|
10
|
10
|
7
|
7
|
8
|
10
|
10
|
7
|
8
|
9
|
10
|
10
|
7
|
8
|
6
|
10
|
10
|
7
|
8
|
7
|
11
|
10
|
7
|
8
|
8
|
11
|
10
|
7
|
9
|
9
|
11
|
10
|
7
|
9
|
6
|
11
|
10
|
7
|
9
|
7
|
12
|
10
|
7
|
9
|
8
|
12
|
10
|
7
|
10
|
9
|
12
|
10
|
7
|
10
|
10
|
12
|
10
|
7
|
10
|
11
|
12
|
10
|
8
|
10
|
12
|
12
|
10
|
8
|
11
|
13
|
12
|
10
|
8
|
11
|
10
|
12
|
10
|
8
|
11
|
11
|
12
|
10
|
9
|
11
|
12
|
12
|
10
|
9
|
12
|
13
|
12
|
10
|
9
|
12
|
10
|
12
|
10
|
9
|
12
|
11
|
12
|
10
|
10
|
12
|
12
|
12
|
10
|
10
|
13
|
13
|
12
|
10
|
10
|
13
|
10
|
12
|
10
|
10
|
13
|
11
|
12
|
10
|
11
|
14
|
12
|
12
|
10
|
11
|
14
|
13
|
12
|
10
|
11
|
14
|
10
|
12
|
10
|
11
|
14
|
11
|
12
|
10
|
12
|
14
|
12
|
12
|
10
|
12
|
15
|
13
|
12
|
10
|
12
|
15
|
STOP
|
12
|
10
|
12
|
15
|