Mathematics 3670: Laboratory 13
Lab Preview
In this lab, we will continue to emphasize issues of parameter passing at the machine level. Of
special interest is how to pass and use pointer values and arrays in the presence of subroutines.
The lab asks you to implement a few new functions and to illustrate their use within a main
program.
Lab Exercises
1. Create a lab13 directory. Place copies of the AshOS files and the function library file
funlib.asm in this directory. In the course of completing the lab, you will add lab13a.asm,
lab13b.asm and lab13c.asm to this directory.
2. Add a new function, swap, to your library of functions. In the C language, this function has
the following prototype:
void swap(int* px, int* py);
Each of the two parameters is a pointer to an int variable. The return type, void, indicates
there is no value computed by this function. In machine terms, each parameter is a memory
address. As shown in the diagram below, we want the swap function to interchange the values
of the corresponding words of memory.
py
px
py
px α
β
β
α
y
x
y
x
Before invoking swap After invoking swap
Follow all the conventions for passing parameters and using stack frames that were established
for Labs 11 and 12.
3. Create a test driver program, lab13a.asm, which illustrates the use of the swap function. In
this program, create four words of memory, initialized as follows:
a: .fill 10
b: .fill 20
c: .fill 30
d: .fill 40
Your program should invoke swap twice: once for the pair aand band a second time for c
and d.
4. Add a new function, sort3, to funlib.asm which will rearrange three words of memory so
they are in order, from smallest to largest. A C language prototype for this function is:
void sort3(int* px, int* py, int* pz);
This function should make pairwise comparisons and perform swaps as necessary. Your code
must make use of the swap function.
