Question

How would you go about creating a subroutine in MARIE assembly language that swaps contents between two memory locations? In this instance the contents for each memory location are names

Answer 1

WE ARE DOING COPY CONTENTS OF FIRST LOCATION AND STORE INTO THIRD LOCATION THEN AGAIN COPY CONTENT OF SECOND LOCATION INTO FIRST AND THEN THIRD TO SECOND,

THIS IS THE WAY WE ARE GOING TO SWAP THE CONTENTS.

CLEAR

  STORE INDEX

WHILE, LOAD STR1_BASE //THROUGH THIS LOOP WE ARE COPYING CONTENT OF FIRST LOCATION

ADD INDEX INTO THIRD LOCATION.

STORE ADDR // FIRST LOAD THE ADDRESS OF FIRST STRING AND THEN ADD OFFSET

CLEAR AND INTO ANOTHER LOCATION ADDR.

LOAD TEMP_BASE //THIS IS OUR THIRD LOCATION

ADD INDEX

STORE ADDR2

CLEAR

ADDI ADDR .// FETCH VALUE AT ADDRESS ADDR .

STORE ADDR2

SKIPCOND 400 // SKIP IF CHAR IS NULL

JUMP DO

JUMP NEXT

DO, LOAD INDEX

ADD ONE // INCREMENT OFFSET

STORE INDEX

JUMP WHILE

NEXT CLEAR

LOAD ZERO

STORE INDEX

WHILE2, LOAD STR2_BASE //SIMILARLY WE WILL DO FOR SECOND LOCATION

ADD INDEX

STORE ADDR

CLEAR

LOAD STR1_BASE

ADD INDEX

STORE ADDR2

CLEAR

ADDI ADDR

STORE ADDR2

SKIPCOND 400

JUMP LOOP2

JUMP AGAIN

LOOP2, LOAD INDEX

ADD ONE

STORE INDEX

JUMP WHILE2

AGAIN, CLEAR

LOAD ZERO

STORE INDEX

CLEAR

WHILE3, LOAD TEMP_BASE

ADD INDEX

STORE ADDR

CLEAR

LOAD STR2_BASE

ADD INDEX

STORE ADDR2

CLEAR

ADDI ADDR

STORE ADDR2

SKIPCOND 400

JUMP LOOP3

JUMP END

LOOP3, LOAD INDEX

ADD ONE

STORE INDEX

JUMP WHILE3

END, HALT