Older blog entries for jdybnis (starting at number 17)

Stupidest Misuse of the C Standard Library

char *name;
...
name[strlen(name)] = '\0';

Found in a codebase that will remain nameless (variable names have been changed to protect the innocent).

Attempt to contribute to glibc

I wrote a patch to give glibc support for profiling multiple shared libraries at once. Right now if you set the environment variable LD_PROFILE to the name of a shared library, glibc will generate gprof style profiling information for that library without you recompiling anything. But that only works with one library at a time. I sent a patch to fix this limitation to the glibc maintainer before the New Year and I've heard nothing back from him yet. Bummer... I don't know if there was something wrong with it, or if it's just not something he's interested in.

I guess I can put the patch up on a web page and let people find it through google. But it seems almost pointless, as it's only a matter of time before the offical codebase moves on and the patch gets stale.

Pining

kwoo:If your only problems with Scheme are that the library is too small, and the function names are too long, then getting where you want to go could be as easy as writing a few macro definitions, and some glue code to hook up the missing libraries you want.

The Development of Weblogs

The way the weblog space (blogspace) is developing reminds me of the web back in 1994. In the very beginning the web was composed of weakly connected islands of pages. The way you found new pages was through external links, like posts on usenet, or addresses published in print mags like WIRED. Likewise when people first started keeping weblogs, you found them through web pages that were not weblogs themselves. There was not any weblog space to speak of yet.

The web quickly formed its own internal entry points, this was the "Cool Site of the Day" model. Weblogs paralleled this, but in a more distributed manner when they started linking to each other. The way you found new weblogs was when the ones that you already read linked to others that they found interesting. This creating a "browsing" user experience.

The next step the web took was with directory sites like Yahoo. Although directory sites originally intended to provide direct links to information you wanted, they ended up augmenting the browsing proccess by making it faster and more efficient, instead of replacing browsing completely. The weblog space parallels this with backlinks, blogrolling, and other technology enabled by RSS. This is the present state of weblogs.

In the eating

graydon speaks as if a test is a boring type of proof. I disagree that a test is a proof, and here is why. He formalizes the notion that testing some case, is equivalent to generating a proof for that case:

any test can be translated into a proof in a silly logic easily: the proof is simply the trace of your processor executing your program's code on your test's input, and the logic is one in which each machine transition that happened is an axiom. but that proof is boring

But remember that a test can fail to terminate. We are not converting the test to a proof, but the execution trace of the test. And that is an impossible task for tests that do not terminate.

Although it could seem like this is a silly technicality, it is big enough that you should not consider a test itself any kind of proof, unless it comes with a proof of termination. To me what distiguishes a proof from anything else, is that there is a totally routine way of checking if it is valid or not. A process that might fail to terminate, does not qualify as totally routine.

Testing Software Can Make it Easier to Prove Correctness

raph mentions Dijkstra's quote that testing can only show the presence of bugs, never their absence

Implied in this is that if you develop a formal proof that a program is correct, then the testing becomes superfluous. But in fact, some types of testing can reduce the burdon of developing the proof.

Instead of proving that a program is always correct, you prove a weaker condition. That is: if the program is correct in one case then it is correct in all cases. Then you write a test to establish that the one case you did not prove actually works.

One specialized version of this technique is, using a proof to establish the induction step of a proof by induction, but then writing a test in order to establish the base case.

sjanes71 and gary are right, directories suck.

Directories are a conflation of the distinct, and sometimes conficting, requirements of naming and classification.

For naming, we want identifiers that are globally unique and stable over time.

For classification, we want categories that are meaningful and can change over time.

The two sets of requirements are conflicting. In particular, we want categories to have globally unique identifiers, but we can not assume that they will have one globally-unique and unchanging meaning.

A lot would need to be done to replace the current system of directories in UNIX. It has a lot of inertia. Practically every program that interfaces with files expects them to be addressable with some variation of /foo/bar/baz. Plus it took a long time to create the stable, fast, and scalable implementations of the system that we have today.

xcyber: sort the tables then compare them.

ksandstr: what do you mean by an idempotent function?

Had a disappointing weekend, where I brought my new computer to an all night quake gathering, only to discover my computer would not run quake!

After hours of forcing other people to swap parts of my computer into their systems, I gave up hope of figuring out what was broken. I spent most of the night playing SSX on a playstation someone had thoughtfully brought with them.

The next day, during a second marathon troubleshooting session I discovered that my ASUS A7V motherboard + GeForce 2 + Win2k were not playing nice. The reason I didn't discover it earlier, was that everyone else had a GeForce 2 too. I should have installed Linux. :)

Anyway, I bought a new motherboard. Now everything is fine and dandy.

And I must say, Cygwin has a pretty slick install program put togeather.