ELEC 2220 Computer Systems
Homework #12
Due: Friday, 9-26-08
1. Rewrite the program for Problem 8 of the midterm quiz, and test it in CodeWarrior.
For convenience, make the array 20 bytes, rather than 200.
2. Design a program to compute A1 = B1 + C1 - D1, where all variables are 32-bit
binary numbers. You may ignore overflow conditions for this exercise. Define the
values of A1, B1, C1, and D1 as 32-bit (4-byte) numbers, stored in “big-endian
format”, using “dc.b” directives. (Recall that the proper storage convention for multi-
precision numbers is for the most significant byte to be stored at the lowest address.)
Example: A1 db $01,$27,$3f,$44 ;A1 = $01273f44
Run the program two times, using the following values.
FIRST RUN: SECOND RUN:
A1 = undefined initially
B1 = $12345678 $fabcdef1
C1 = $4567bcde $ffffffff
D1 = $2345ef01 $eeeeeeee
Print one copy of your program and the two Code Warrior debug windows, circling or
highlighting the values of the four variables after each run.
Notes:
1. Multi-precision arithmetic requires the use of add-with-carry and subtract-with-
carry.
2. If adding, an entire multi-precision result must be computed before moving on to
another operation.
3. Consider using loop structures to do the operations needed for the 32-bit add and
the 32-bit subtract.
