CPTR-215 Assembly Language Programming HW#9 Due Wednesday

Finish reading chapter 6 if you have not already done so.

Suppose you need to divide two integer numbers. Some CPUs do not have division instructions (ARM is one of those). A simple way to do division is to repeatedly subtract a positive divisor from a positive dividend while counting the number of times this can be done before the result is negative. The quotient is the number of subtractions performed.

Note: to confirm understanding of the algorithm, use pencil and paper to divide 10 by 3. Starting with 10, repeatedly subtract 3 and make a list of the results until the result becomes negative. Count the number of subtractions before the negative result. Observe that in a program you will need to do an extra subtraction before you know that a negative result has occurred. Your program can then correct the results accordingly.

Write a short assembly program to demonstrate division via subtraction as defined above. Register r1 should be loaded with the dividend and r2 with the divisor. When the program finishes, r3 should contain the quotient and r4 the remainder. Before writing the assembly code, design the program, document it with either NS diagrams or a flow chart. Then code it (i.e. create the assembly language file), assembly it, and test it.

This method requires large run times if a large number is divided by a small number. Test your program. In particular, test it using the following cases:


Turn in: a copy of your design document and a hardcopy of your source file (.s file). On it report if the program worked or not and if or not you were able to use the debugger to monitor program operation. Comments about your experience, trials, tribulations, unexpected successes, etc. are welcome.


Larry Aamodt PhD, PE
Professor of Engineering and Computer Science
Walla Walla College
Contact:
via email: AamoLa (at) wallawalla.edu
via phone: x2058