Month: October 2010

I keep running into this and doing my standard google-up-the-answer-routine didn’t seem to be working.

In short, ucspi-tcp doesn’t compile on CentOS boxes (or RedHat boxes). Cuz DJB doesn’t “believe in” RedHat’s “you must have an errno.h” thing. Hey, I love DJB, and his software, but I also think he’s impractical and a nutjob sometimes. This would be one of those times.

Lots of folks had patch-related ways of fixing the problem, I thought those seemed rather laborious. I just stole The Internet’s method for another DJB package.

Just append -include /usr/include/errno.h at the end of the first line of conf-cc so it looks like this:

gcc -O2 -include /usr/include/errno.h

This will be used to compile .c files.

Boom, everything works now.

So Beckley got a hold of the MetroCard Math site and built on top of David’s fantastic work to build even more prettiness, neat-workingness, and general niftitude into the site.

We also put in a thingee – well, by ‘we’ I mean ‘he’ – he put in a thingee that lets you see how the new price changes will affect you. For me, I definitely will be sticking with the pay-per-ride.

And another thing – I actually tested the new (divisible-by-a-nickel) magic number, and it *does* work. My MetroCard has an exactly even number of rides on it. Cool. Now I just have to do something with all these MetroCards that have 10 or 20 cents on them – perhaps a new part of the site that lets you put in how much money is on your cards, and then it tells you how much more to put on to get it ‘even’? Not a bad idea…

Gory Details: so, talk to any computer sciencey person and they will always tell you that Floating Point Math is Hard. I have only rarely run into this, but the rounding algorithms are very specific when you buy stuff, and if you’re off by a penny, then, well, you’re off by a penny, and things stop working. We found a couple of minor (off-by-one) bugs here and there, and every time it seems like I fixed one, the rest of the results would start to go haywire. The real problem is that I am trying to ‘move’ the rounding around the formula:

round_for_money($x * 1.15) = n * $2.25

Now solve for ‘x’, and let ‘n’ be any integer – well, that pesky ’round()’ is in the way, and if you just try to move it to the other side, or round at some random and/or inopportune time, then when you get back to the original equation, sometimes the numbers don’t work out anymore. It sucks.

So I racked and racked my brain trying to figure out a way to do my simple solve-for-x routine. I really just want to try different integers for ‘n’ until I find an answer that’s “acceptable.” But that doesn’t work. At all. Or at least, I don’t know what mathematical operation I can do to move that round() function off the left side so I can try to have a formula that points to ‘x’.

What did I do finally? I gave up. I left the formula as it is above, and just run ‘x’ from 0 to “a lot” (a thousand bucks or a hundred bucks I think?). The answer I get is going to be completely accurate, but it wastes computing power. Well, too bad, your browser has to do a little bit of multiplication in a loop. My condolences. But! The result is, I’m pretty convinced my answers are to-the-penny accurate now. We’ll see when the big price change kicks in.

Thanks again to David Dominguez for the initial switch to jQuery-powered MetroCard Math, and thanks to Beckley for the full re-skinning he pulled off.

So I’ve updated my Metrocard Math site.

First, my friend David Dominguez helped out to make it much, much prettier. He also added some jQuery magic, and changed up a significant amount of how the site is structured. I was trying a weird idea – where I would strip the markup down to its most basic elements, and style it from there using cleverly-constructed css selectors, but I don’t think it worked out. My friend Bryan tried to restyle it as well, and the rigidity of the markup basically stopped him in his tracks. So, anyways, now it looks prettier and is definitely more usable on my phone.

I also had tried to buy a metrocard for one of the Magic Number amounts the other day at a vending machine, and it was rejected due to “invalid amount.” Stupid. It had worked before. I tried the small number. I tried the big number. Nothing worked. On a hunch, I tried $11.75 instead of $11.74. Success. And of course, I will eventually have a metrocard with a penny on it. So apparently, the number has to be divisible by 5? So I’ve added that to the site, and we’ll see when I next buy a metrocard if the new system actually works. I hope they don’t make it where it has to be divisible by $0.25, that would really sting.

I still want to do something where you can toggle between the current prices and the newly announced ones. But right now you can just type in the new numbers – Here’s what they are according to the Queens Chronicle (which I used to consult for a million years ago!) $104 is the new 30-day, $2.50 is the new single ride, and $29 is the new 7-day. The one-day funpass is going to be eliminated and so will the 14-day unlimited. Oh, and I hadn’t seen this before – there’s now going to be a $1 surcharge every time you pick up a new metrocard (though that doesn’t start till some time in 2011) OUCH. That means when you leave your metrocard at home and have to buy another one it’s *really* going to sting. One more extra buck. Damn. I mean, you can still use the lastest magic number ($15.65 I believe? Though I worry my rounding might not match the MTA’s…), but you definitely will not want to be throwing out your metrocards anymore.