I looked up at the beautifully clear night sky yesterday, and noticed that the stars actually looked to me as if they were different distances away.

Now I know perfectly well that human binocular vision can't possibly resolve distances of that magnitude. It therefore struck me as odd that I was perceiving something which I knew to be both an optical illusion, and true!

The other day I needed a lot of primes in a hurry, and I judged that it would be quicker just to sit down and write a simple Sieve of Eratosthenes program from memory than to faff about trying to google up one that somebody had already written and that wasn't in some unhelpful language.

So I wrote one; then I disposed of the obvious bugs by checking its output rigorously for numbers up to 10; then I ran it for numbers up to 100 and didn't see anything obviously wrong (though I didn't look that hard). Then I wondered whether there was any good way to be more confident of its correctness.

On a whim, I made it generate all the primes up to 2^32, and fed the output text file to md5sum (with Unix line endings). Then I pasted the resulting checksum into Google – and found a hit! Somebody else had generated the same set of primes, checksummed them in exactly the same way, and posted the MD5 on a web forum which was talking about prime-generating programs so that other people on the forum could use it as a test case. Just the confirmation I wanted.

The silly thing is that if I'd tried to google for things like ‘md5sum of primes up to 2^32’, it wouldn't have been remotely successful. But once you already know what you think the answer is (at least in cases where it's a mess of digits), googling for that will tell you whether anyone else agreed with you.

Last month I went to Borders, in Cambridge town centre, and bought a pile of paperbacks.

This evening I was sitting on my sofa reading one of them; I turned a page and found a receipt stuck between the pages. A receipt for the book I was holding – from WH Smith, in Cambridge town centre, dated February of this year.

What happened there then? Best explanation I can think of is that somebody bought it from Smiths and then managed to leave it behind somewhere in Borders – perhaps in the café – and when the Borders staff came to clear up they saw a pristine paperback, assumed it was part of their stock, and shelved it. How strange. I wonder if I ought to notify somebody.

You know the Internet has taken over your brain when you find yourself typoing ‘relolcation’. Or ‘allolcation’.

Underambitious fantasies. My back was itching in the pub last night, and I couldn't quite reach the right spot to scratch it. ‘If only,’ I heard myself think, ‘I had a slightly longer arm.’

Ridiculous! If I'm going to allow myself to fantasise counterfactually, why didn't I just fantasise ‘If only my back didn't itch in the first place’?

That well-known software design adage: ‘Make simple things simple, make difficult things possible.’

The implied word in the middle is ‘and’, not ‘or’!

Occasionally I feel just a little like Rimmer at work. This morning I sent an email response to a bug report from the support department, saying something along the lines of

Can you explain a little more about why you expect this to work? The C99 standard clearly states (section 7.19.7.3 clause 4) that…

and somewhere in the back of my head, Kryten is responding ‘Section 7.19.7.3 clause 4? No member of the support department shall raise a defect report while wearing a ginger toupée?’

crazyscot's recent LJ post about a factor-of-20 speedup of some code reminds me that I've never written down in here the story of my first summer job, despite it being a standard anecdote I use in real life when I get into those ‘the worst code I've ever encountered’ geek war-story conversations.

( some of the worst code I've ever encountered, and how I too sped it up by a factor of twenty )

The boss took one look at the speed test, and shook his head. ‘We can't ship that,’ he said, ‘it's far too embarrassing. We'll have to deliberately slow it back down again, and ship lots of incremental speed upgrades.’

I laughed.

He turned out not to be joking.

Blindness to the difference between positive and negative incentives. If there are two options, of which someone is currently choosing option A and you'd like them to choose option B instead, you can attempt to achieve this in two ways. You can increase the attractiveness of B to more than that of A, or you can reduce the attractiveness of A to less than that of B. Both of these have a good chance of changing behaviour, but the former makes the people it affects happier, while the latter makes them less so. Doing the latter when you could reasonably have done the former, or acting all surprised when you do the latter and people mysteriously don't seem to be happy about it, considered irritating.

Things that are simultaneously interesting and tiresome. Whether it's a potentially interesting topic of discussion but most people tend to focus on the boring bits, or whether it's interesting in principle but long since done to death, or whether the tiresomeness of the fact that it needs to be argued about at all is in opposition to the interestingness of some of the actual arguments, or whether the interesting and tiresome parts can't even be separated like that and the problem is just that my brain can't make up its mind whether it likes it, or (in extreme cases) all of the above. It's fair enough in this morally complex world that things can be both good and bad, but one might naïvely have thought it should at least be possible to reach a conclusion about whether any given thing was interesting or not. Gah.

Finally managed to get my music font up on the web this morning, after nearly a week of last-minute pre-release polishing. I swear, every time I publish something, it seems to take longer than the last time to sort out all the fiddly details like licences and distribution archives and READMEs and so on.

For anyone interested, I've put it up at http://www.chiark.greenend.org.uk/~sgtatham/gonville/.

Now I can have a rest, and then do something completely different.

For the benefit of anyone who's interested and who hasn't already had me talk their ears off about this, here's a discussion of the techniques I used to design the music font I've been talking about recently.

( this gets long, and also mathematical )

In case anyone has the energy to try to think up names based on what the font actually looks like: a couple of small sample images showing the difference between my font and standard Lilypond are visible in the comments to last week's post.

Bah. Onion-chopping incompetence last night has left me trying to type without using my left index finger, at least for a day or so until I'm sure healing is well under way.

Most of my typing style has adapted reasonably well (I often think this sort of flexibility is an advantage of having learned to type simply by typing a lot instead of doing one of those formal home-keys courses), though it's slowing me down noticeably so I have more of an incentive to engage brain before putting fingers to keyboard.

The really hard thing, though, is passwords. Everything else I can think about how to type if in doubt, but passwords are mostly stored in my brain as muscle memory, which isn't directly applicable so I have to painstakingly translate the stored muscle movements back into characters.

Hmm, I seem not to have posted anything in here for months. I'm not quite sure whether my life has been more boring recently, or whether it's just that my interestingness threshold for bothering to post in this diary has gone up.

I've had a new silly project preoccupying me since I last posted, which is to arrange a means of computer-typesetting music that doesn't irritate me. Until now I've been using a program I wrote myself when I was 15 and have stuck with on the grounds that I already knew how to use it and it's just about good enough, but it shows definite signs of having been written by a 15-year-old, and in particular the copyright status on its font of musical symbols was uncertain so I couldn't distribute it. Every alternative I've looked at since then has irritated me for at least one reason, and in particular I haven't found any replacement set of symbols that were both to my taste and copyright-unproblematic. So in the last couple of months I decided enough was enough and drew a new set from scratch, and then dropped that into the least irritating of the existing typesetting software. As of the weekend just past, the result is passing its stress test collection and I think I prefer its output to everything else I've seen including my own program. I can witter on about this at much greater length if anyone is interested and hasn't already been subjected to two months of said witter in the pub :-)

Last week I finally got round to dealing with the fact that nobody is currently selling acceptably nice gluten-free pizza bases, by experimenting with my breadmaker's pizza dough setting. This was successful after a couple of attempts (and even the first attempt wasn't too bad), so I now have a sudden urge to feed pizza to everyone I know.

Other unexpected things that have happened to me in the last couple of months include unexpectedly being called on to help catch a young woman jumping off a roof (she'd apparently climbed up there for a laugh and then found getting down was harder than getting up; I was walking past at the time), accidentally re-proving a theorem of Erdős in conjunction with drswirly (it struck me as an interesting question and we managed to prove the answer before finding out who'd already done it), accidentally finding the inverse cosine of 0.9 (a number I picked completely at random was so close to it that it completely confused a test program I was running) and having a cold while on holiday (bah).

At aiwendel's birthday party on Saturday there was a considerable amount of impromptu music-making. In particular, there were spare violins lying around, and I picked one up and had a go on it.

The next morning, however, all the embarrassment came back. I don't often get that ‘oh god, what did I do last night?’ feeling after parties, but yesterday morning I suddenly felt as if I'd made a huge, attention-seeking prat of myself for the entire evening by pretending to violin-playing skill in public.

On the other hand, curiously, my left wrist felt fine this time (though my right shoulder was killing me for most of yesterday, but that seems less likely to be caused by violin-playing – I probably just slept funny). So now yesterday's retrospective embarrassment has worn off a bit, I feel almost tempted to scrounge a cheap violin from somewhere and have another try at it in the privacy of my own home (and then perhaps risk exposing other people to it again after I've practised a bit).

I suspect it's probably still a bad idea, on balance: just because I didn't manage to hurt my wrist noticeably in one evening doesn't mean I wouldn't still do it cumulative damage if I kept it up for longer, and really, I do depend on my wrists…

An Amazon Marketplace seller just managed to deliver a book to me so quickly that the Amazon website won't let me leave my seller feedback (‘This order is not yet eligible’).

I had taken a chance with this order, by buying from a seller which Amazon reported as ‘just launched’, and hence who had no previous feedback at all. Perhaps that's why – perhaps they're not actually that new, they just deliver so quickly that it confuses people!

A bit of correlation analysis between the questions in my recent LJ poll said that, slightly to my surprise, the number of people who thought they were better at remembering to do things compared to the general standard they ascribe to other people was exactly the same as the number who thought they were worse. I was expecting this to be the sort of question where most people think they're above average (as is often claimed about driving), but failing that I'd at least have expected some sort of correlation. Gosh.

I managed to cut a finger last night on a plastic saucepan handle while washing up. I'm still not entirely sure how it happened. However, I've learned a new respect for my left ring finger; trying to avoid using it for the rest of the evening made computer use very awkward. It seems to do all the nearly-unconscious parts of my typing style.

One morning years ago I happened to wake up half an hour early and then realised it was election day, so I got up and went to vote on the basis that it was something useful to do with the extra half-hour in my day and then I wouldn't have to remember to do it later. My subconscious must have thought that was a good idea, because I've woken up early on election days more often than not since.

The polling station this morning handed me an EU ballot paper literally as long as my arm. Might have been nicer if they'd also provided voting booths containing tables big enough to hold it!

‘UPS hereby notifies you that we have received electronic information about this package we're supposed to be sending to you. We may or may not have received the actual package, but we know we've got the electronic information. For more details, see the following tracking URL which will still tell you we don't know if we've got the package or not. P.S. The colour brown is a vigorously defended trademark of United Parcel Service.’

Looks to me as if someone's been putting more effort into IP land grabs than into the sanity of their tracking system…

Having just ranted about problems that I forget about as soon as they're fixed, I thought I'd balance things out by mentioning a problem which has surprised me by not having this property.

In 2000 I moved out of a shared house to live on my own in a first-floor maisonette flat, i.e. the upstairs half of a semi-detached house. In 2003 I moved from that flat into another (nicer) first-floor maisonette flat. So by late 2007, when I bought a proper house, I had been living exclusively on the first floor (apart from tiny entrance halls on the ground floor) for just over seven years.

I was a bit nervous about that, to begin with. I had an irrational worry that I might have – in some unspecified sense – forgotten how to deal with having a ground floor. Perhaps I'd accidentally leave windows open and get burgled. Or perhaps I'd have forgotten how to stop Jehovah's Witnesses from getting a foot in the door (which is very easy in a first-floor flat – you just shout down at them from the window above the front door, and never open the door at all). Or perhaps I just wouldn't feel right without those eight feet of vertical distance separating me from the ground: an Englishman's home is his castle, after all, and castles are more convincingly defensible when situated high up.

But my worries were unfounded. Pretty much as soon as I moved in, it was immediately clear that I had in fact missed having a ground floor – I just hadn't realised it before I got one back. I felt a great sense of rightness at being able to walk around downstairs and not hear the creaking of dodgy floorboards beneath my feet. (And even walking around upstairs, where the floorboards still do creak, became more pleasant once I knew the noise wasn't disturbing a downstairs neighbour.) It's important to me to have a properly solid floor at the bottom of my home, it turns out; and although I had apparently been suppressing that need so well that I hadn't realised I had it, it was there, and suddenly it was fulfilled.

I was fairly sure, back in 2007, that this would turn out to be one of those ex-problems quickly forgotten about: that the delight of not having creaky floorboards under me was a passing thing, and that after a week or so of feeling relieved I would thereafter just feel neutral about it.

But no. Rather to my surprise, I didn't get over it that quickly, and in fact after over a year and a half living here I still haven't. Every day or two I still get up from the sofa, take a few steps, and feel real pleasure at the fact that I'm walking on a real solid surface, there's no give in it beyond the carpet pile, and the only sound I'm making is the whisper of socks on carpet. Quite often I find myself gratuitously pacing back and forth just so I can enjoy it for longer.

(Good job, too: given how much money I spent on acquiring a ground floor, it would seem particularly irritating if I'd forgotten about it immediately!)

As I said in my previous post, it feels to me as if ideally one ought to be able to derive enjoyment from the absence of an irritation for about as long as the irritation persisted to begin with. By that measure, I hope not to get over this one before 2014. I wonder if I will.