Question
17.
Write code to implement the expression A = (B + C)
(D
+ E) on 3-, 2-, 1-, and 0-address machines. In accordance with
programming language practice, computing the expression should not
change the values of its operands.
Answer
Three address machine: Computers with three address instructions formats can use each address field to specify either a processor register or memory operand.
|
ADD |
R1 , B , C |
R1 ß M[B]+M[C] |
|
ADD |
R2 , D , E |
R2 ß M[D]+M[E] |
|
MUL |
A, R1 , R2 |
M[A]ß R1 * R2 |
Two address machine: two-address instruction are the most common in commercial computers. Here again each address field can specify either a processor register or memory operand.
|
Load |
R1 , B |
R1 ß M[B] |
|
ADD |
R1 , C |
R1 ß R1 + M[C] |
|
Load |
R2 , D |
R2 ßM[D] |
|
ADD |
R2 , E |
R2 ß R2 + M[E] |
|
MUL |
R1 , R2 |
R1 ß R1 * R2 |
|
Store |
A , R1 |
M[A]ßR1 |
One Address machine: One-address instructions use an implied accumulator (AC) for all data manipulations. For multiplications and division there is a need for second register.
|
Load |
B |
ACßM[B] |
|
ADD |
C |
ACßAC+M[C] |
|
Store |
Temp |
M[Temp]ß AC |
|
Load |
D |
ACßM[D] |
|
ADD |
E |
ACßAC+M[E] |
|
MUL |
Temp |
ACßAC*M[Temp] |
|
Store |
A |
M[A]ßAC |
Zero Address machine: A stack organized computer does not use an address field for the instructions ADD and MUL. The PUSH and POP instructions however need an address field to specify the operand that communicates with the stack. To evaluate arithmetic expressions in a stack computer , it is necessary to convert the expression into reverse Polish notation
|
PUSH |
B |
TOSßB |
|
PUSH |
C |
TOSßC |
|
ADD |
|
TOSß (B+C) |
|
Push |
D |
TOSßD |
|
Push |
E |
TOSßE |
|
ADD |
|
TOSß(D+E) |
|
Mul |
|
TOSß(B+C)*(D+E) |
|
POP |
A |
M[A]ßTOS |