Advogato blog for ingvar

19 Feb 2010

Fri, 19 Feb 2010 10:08:08 GMT

This morning, I finished off and packaged up a library (CL, linux; other OSes with CL implementations and OS-provided random (or random-backed pseudorandom) devices can probably be grafted in, but would require volunteers to test) to extract random bits from /dev/urandom and use those essentially unadorned to generate random numbers.

There's a single exported function from the package, RANDOMNESS:RND and takes an integer argument (I guess you could try feeding it a float, but it wouldn't do you that much good). That function then proceeds to extract log₂ N bits and uses rejection smapling to find an integer in the 0..(N-1) span. As the bits sucked out of the internal pool run out (each bit is used only the once), they're replenished from the OS-provided randomness source.

All very nice, with some interesting corner cases for the unwary and probably still bug-ridden. But, such is life.

Download from here.

3 Dec 2009

Thu, 3 Dec 2009 11:58:51 GMT

Neat(ish) hack...

Sometimes, I find myself writing anonymous functions, to fill out keyword arguments for functions or adapting the argument order. So, I thought, how hard would it be to write a macro to write the code for me? Turns out, not very complex, at all. The formatting is not QUITE what I started out with, as the Advogato edit box is a bit on the short end, but, hey...


(defmacro _ (form)
 (flet ((is-arg (sym)
	  (ignore-errors
	   (and (char= (char (symbol-name sym) 0) #\_)
		(cons
		 (parse-integer (symbol-name sym)
				:start 1)
		 sym)))))
   (let ((syms (loop for arg in form
		  for temp = (is-arg arg)
		  if temp collect temp)))
    `(lambda
	 ,(mapcar #'cdr (sort syms #'< :key #'car))
       ,form))))

With this in hand, you can, for example, easily make an adapter to parse C-style hex constants:


  (_ (parse-integer _1 :radix 16 :start 2))

Not that the lambda-wrapping of this would've been much more complex and I am not entirely sure this wins as far as readability is concerned, but that is as it may be. It's if nothing else a neat macro that would be more than a little tricky to pull off with a less capable macro facility.

27 Nov 2009

Fri, 27 Nov 2009 08:19:54 GMT

So, one of the users of my Image library asked if there wasn't any way of using a font other than the rather ugly, built-in one. I said, roughly, "you can define a new one, in an analogous fashion to how the built-in oine is done?"

Apparently, that was not the wished-for answer and I started thinking. Bit-mapped fonts are (relatively) easy to deal with. There's a helluva lot of bitmapped fonts for X11. So, I set forth to code up a reader for PCF fonts, converting the bitmaps to internal format and some multi- font support in Image. All done, now.

Common Lisp is still very pleasant when dealing with binary file I/O, even if I wished that there was an easy way of changing the binaryness of a file on the fly.

18 Nov 2009

Wed, 18 Nov 2009 09:53:52 GMT

Currently tooling away at asked-for functionality for my IMAGE library (specifically, a request was made to see if I can scare up another font or three, so I am currently noodling on a PCF font-file reader, as you do).

Common Lisp continues to be amazingly convenient for "binary I/O", although it does require a certain mind-set to consider it convenient, I guess.

13 Nov 2009

Fri, 13 Nov 2009 10:06:20 GMT

I've just packaged up a new release of my IMAGE library, with some new functionality in place. It now supports copying (parts of) an image into another image (with either the same alpha across the whole copied section or with a provided alpha map, so one can do Clever Stuff that way).

I suppose I should write documentation for the image library at some point, but...

6 Oct 2009

Tue, 6 Oct 2009 15:15:11 GMT

Idleness is the source of many bugs. I suppose. It's certainly the cause for a lot of code I write.

Lately, I have been pondering hashing of octet vectors. Well, actually, I've been pondering the hashing of strings, but these days strings need mangling to octet vectors before one can reasonably reason about them as numbers (in my case, turning a vector of characters into a possibly- longer (well, possibly-more-elemented) vector of (UNSIGNED- BYTE 8), containing a UTF-8 encoding of the character string).

But, what's a hash without an idea how well it performs? So, with a pluggable (or at least semi-pluggable) hash algo, what I now do is run it across a dictionary (in my case it is /usr/dict/words, containing a British word list) and see how many collisions one gets.

The next step is, of course, to try to figurte out what is and isn't bad, as far as collissions go. From memory, the last attempt say something like 600 collisions out of just under 70k words. I'd have to run a simulation to say if it's well above, well below or around what I'd statistically expect.

Next after that will have to be concatenations of words, though that MAY take a bit longer to test-run.

22 Sep 2009

Tue, 22 Sep 2009 16:24:23 GMT

Interesting (but rather pointless) self-replicating shell- script:


#! /bin/cat
Self-replicating!

Make sure it's executable, then you can replicate the whole script by running it... But, maybe, there's some usefulness to it? Doubt it, though.

4 Sep 2009

Fri, 4 Sep 2009 14:23:49 GMT

IN slightly less whingeing news, since the latest (well, second) installment of the annual Snooper Report has been turned down, I'll let it loose on an unsuspecting public (and, of course, the URL is too wide for the Advogato editing window, so now I'll get bots come and look for URLs with %0A in them, grr).

In almost as exciting news, I cobbled up a proof-of-concept of a blackhole maintenance library (CLI client, web client, libarry code, DB backend and a reaper suitable to stick in cron, to remove blackholes once they expire).

4 Sep 2009

Fri, 4 Sep 2009 13:10:32 GMT

One of the little web toys I knocked together and occasionally use for pontificating is my Essays site. Since its initial creation, I've added a comment functionality, but due to the prevalence of spam, everything requires manual verification.

Not, in and of itself, a major problem, but I've noticed something quite disturbing in the spam comments (most, alas). The latest is that they're pointing to the SourceForge forum (with URLs that start http:// cmr.sourceforge.net/forum/) and I am in two minds about that.

One mind says I shouldn't bother complaining, because they should already have noticed. The other mind says I should, indeed, point it out to them (with a slight risk that the forum is zapped; this happened last time I pointed the issue out).

Instead, I decided that thee Right and Proper thing to do is to have a semi-public whinge. Don't know that it makes me feel any betetr, but at least I am not feeling any worse.

9 Aug 2009

Sun, 9 Aug 2009 10:47:56 GMT

I have previously written a short essay, or possibly a rant on "develop and release straight out of version control" or "release in versioned lumps of code, with the development being separate".

That whole thing just jumped to the fore-front of my mind, as it seems that SLIME has changed under my feet again (no, I didn't intentionally upgrade SLIME, but it seems as if I need to stop getting SLIME via Debian and instead pull it myself, so it stops changing when the rest of the system upgrade; I also need to downgrade the SLIME I have installed as whatever I run now is less functional (for me) than what I ran prior to the last upgrade).

I don't know if things would be better or worse if "package and release" was the dominant paradigm, though. It'd probably cause less friction with an auto-update system that is tailored to packaged and versioned releases.