17.7 Testing

This is not a program that you want to write in a single session. I suggest that you write the subroutines in the following order.

• readdec.s: this is a conversion (to use stack-based local variables and etc.) from a previous project. Test it individually.
• sort.s: implement it so that you can at least read the input file (probably from redirection) and store numbers in an array.
• printdec.s: this should be the same as in project 3.
• sort.s: implement it so that you can print numbers from the array. Verify that the program reads and writes integers correctly.
• pivot.s: get the subroutine pivot to work. You need to modify sort.s to call pivot. Just make sort.s call pivot once and make sure the array is pivotted correctly, and that the index of the pivot is computed properly.
• sort.s: modify the main program again to call quicksort instead of pivot.
• quicksort.s: this is the recursive subroutine. Interestingly, if you have done everything correctly up to this point, this subroutine is also one of the simplest!

The key is to do incremental programming and debugging. Version control may be helpful as well. Try to apply the techniques that I discussed in the class when I demonstrated how to implement readword in project 3.