2024-08-02 20:17:29 <KipIngram   > It's funny how often that fails to get mentioned when it's the case.
2024-08-02 22:05:58 <KipIngram   > Hey, just a little tidbit it might be handy to have in mind at some point.  Bash arithmetic doesn't seem to handle modulo operations (% operator) right.  It's fine for positive numbers, but for example -1 % 10 returns -1, whereas I think it should be 9.
2024-08-02 22:06:13 <KipIngram   > It's probably not "wrong" - there's  probably a reason it's fine.  It's just not what I expected or needed, though.
2024-08-02 22:06:40 <KipIngram   > Python, for example, returns 9 for -1 % 10.
2024-08-02 22:07:45 <KipIngram   > Bash seems to do the operation as though the number were positive, and then put the - back on when it's done if it was there to begin with.
2024-08-02 22:09:50 <darkling    > I think there's two opinions on this point: is % the mathematical modulo operator, or is it "remainder after division"? Those are the same if both operands are positive, but differ if one of them is negative.
2024-08-02 22:10:20 <thrig       > modulus isn't portable between languages
2024-08-02 22:10:30 <KipIngram   > Right.
2024-08-02 22:10:45 <darkling    > I think remainder-after-division is easier to implement on a reasonably normal CPU, but mathematical-modulus is usually easier to work with.
2024-08-02 22:10:48 <KipIngram   > I think of it like "clock arithmetic."  Noon minus one hour is 11.
2024-08-02 22:11:09 <KipIngram   > Or at least that's how it suited me to think of it for what I was just doing when it came to my attention.
2024-08-02 22:11:42 <KipIngram   > I'm measuring the handhake time between my system canisters at work.  I do that by gettng the time in ms, doing the handshake, and getting the time in ms again.
2024-08-02 22:11:49 <darkling    > Like I said, the mathematical version is usually what we actually want, but it's rarely (IMO) what we're given. :/
2024-08-02 22:11:51 <KipIngram   > And I needed to watch out for rolling over midnight.
2024-08-02 22:12:09 <KipIngram   > I thought modulo 86400000 would do the trick, but it doesn't because of this.
2024-08-02 22:12:23 <KipIngram   > Before I subtract I check, and if the second one is smaller I just add 86400000 to it.
2024-08-02 22:13:23 <darkling    > That's usually what you've got to do, yes. Or (x % n + x) % n, if you don't want a conditional in the expression (and don't care about computation cost too much).
2024-08-02 22:13:53 <KipIngram   > Ok, well, I'm glad this is a known issue - I'd just never bumped into it before.
2024-08-02 22:15:07 <KipIngram   > The recent big outage we had after hurricane Beryl seems to have damaged out network at the office - ever since then my jobs have started getting stuck periodically, on these handshakes.
2024-08-02 22:15:24 <KipIngram   > It was poor initial coding on my part - I was just sending an ssh command and presuming it got there.
2024-08-02 22:15:42 <KipIngram   > I modified it so it expects something as a result of that command and confirms it, and re-tries if it gets a timeout instead.
2024-08-02 22:16:07 <KipIngram   > I was guilty of "coding for the good path."
2024-08-02 22:16:18 <darkling    > It's either that, or the network's Just Had Enough of This Shit.
2024-08-02 22:16:21 <darkling    > I know how it feels.
2024-08-02 22:16:24 <KipIngram   > But, it did work fine for three years, so...
2024-08-02 22:16:32 <KipIngram   > :-)
2024-08-02 22:17:11 <KipIngram   > Adding the lag measurement wsa just a little frill I thew in as long as I was in the neighborhood.  Writing those out the session logs.
2024-08-02 22:17:30 <KipIngram   > "to"
2024-08-02 22:17:46 <KipIngram   > So far it looks like 200-300 ms is "normal."