## xv6

I’m teaching a small Advanced Operating Systems course this spring. Preparing for the course over winter break, I spent some time reading various Linux subsystems such as the scheduler, and was a bit shocked at how complex it has become. I’ve been using Linux, looking at its code, and occasionally hacking it for more than …

## That Was Easy

I wanted to play around with the Python interface to Z3 and the classic SEND + MORE = MONEY puzzle seemed like a good way to get started. This turned out to be so easy that my code worked almost on the first try: Then: \$ python ./send_more_money.py sat D = 7 S = 9 …

## Writing Solid Code Weeks 7 and 8

The students continued with their compressor/decompressor development. Coverity continued to find plenty of issues for the students to fix. I’m about to start doing a bit of differential testing of their code, using voting to determine who is correct and who is wrong. I lectured on paranoid programming and on building a fuzzer, for sort …

## Writing Solid Code Week 4

This week most of the students in the class (but not everyone, since we ran out of time) presented their arguments about the quality of various UNIX utility programs. This was a bit more interesting than it might otherwise have been since some of the utilities running on our student lab machines are hilariously old …

## Writing Solid Code Week 3

This week we finished up the triangle classifier. Not all students’ implementations pass all test cases, which is totally fine with me as long as people learned some lessons about when not to use floating point (I did). On Tuesday we also chose a smallish UNIX utility for each student to evaluate as if it …

## Writing Solid Code Week 2

First, I wanted to thank everyone for the great discussion on the post about week 1. My single favorite thing about blogging is the discussion and involvement that these posts sometimes generate. During week 2 we worked on issues relating to the triangle classifier. As several commenters predicted, getting correct results using floating point code …

## FizzBuzz Bugs

It is said that an overwhelming majority of applicants for some programming jobs fail the FizzBuzz test. As part of a simple warmup exercise, I asked my computer systems class (a required course for CS majors, usually taken in the 3rd year) to implement FizzBuzz in C. The problem statement was, I think, the standard …

## MSCS

A masters of science degree in computer science can mean two very different things: The research MS where the student works closely with an advisor on a research project that culminates in a thesis and ideally a few papers. This kind of student is generally paid as a TA or RA and can be expected …

## Procedural Decomposition

While teaching a CS class I spend quite a bit of time looking over the shoulders of students whose code doesn’t work. Sometimes they have a simple mistake and I’ll either point it out or ask a question that will lead them to the problem. However, other times the code is just generally not very …

## Reading Code

Reading code is an important skill that doesn’t get enough emphasis in CS programs. There are three main aspects: the external view of the code: documentation, comments, APIs, white papers, information from developers, etc. the static view: reading the code like a book the dynamic view: reading the code as it executes, probably with help from …