Hulver's site || thanks everyone who congratulated me with a new job

Diaries
Everything
Who's Online?
FAQ / Help

thanks everyone who congratulated me with a new job

By i (Fri Dec 22, 2006 at 07:14:25 AM EST) (all tags)

now to our little C puzzle.

ok, here's a function.

int safe_division (int a, int b) { retun b ? (a / b) : 0; }

is this code safe? is it? is it? i'm asking you!

well, cow could it be unsafe?

it is unsafe. it can and does crash on common architectures, such as IA32. honest. try to figure out that rare combination of inputs.

< Early Consumer-mas | BBC White season: 'Rivers of Blood' >

Related Links

- i's Diary

Google

Comment Controls

thanks everyone who congratulated me with a new job | 15 comments (15 topical, 0 hidden) | Trackback

uh by komet (2.00 / 0) #1 Fri Dec 22, 2006 at 07:32:17 AM EST

when you say "crash", do you mean it takes over your computer and installs spyware and a kiddy porn server?

--
<ni> komet: You are functionally illiterate as regards trashy erotica.

probably means by sasquatchan (2.00 / 0) #5 Fri Dec 22, 2006 at 09:50:27 AM EST

crash because someone didn't feel like writing correct code to catch exceptions and handle them in a graceful manner.

[ Parent ]

What kind of person by ambrosen (2.00 / 0) #7 Fri Dec 22, 2006 at 10:14:52 AM EST

Kernighan, I mean, can't even be bothered to check that sort of failure. Let alone building the ubiquitous processor architecture to fail on a division. Oh wait, it's a result of twos compliment negative numbers.

Another in the series of i's great teasers, I guess.

[ Parent ]

: it's a ha-ha only serious by sasquatchan (2.00 / 0) #13 Fri Dec 22, 2006 at 10:23:17 AM EST

in that most code I deal with has a near top-level try/catch that catches (...) and usually just kills the thread. SEH has good and bad points, (most) everyone says "it(SEH) is a good thing," but then goes and writes code with no real exception handling.
(Mainly because 'doing it right' can easily triple your lines of code...)

[ Parent ]

well it could by i (4.00 / 1) #10 Fri Dec 22, 2006 at 10:22:13 AM EST

i'm not aware of any machine that actually does that, but you know, it's not prohibited by the standard.

[ Parent ]

Complete guess by TPD (2.00 / 0) #2 Fri Dec 22, 2006 at 08:11:36 AM EST

some wierd branch prediction issue forcing the division (and subsequent error flagging) when b is 0.

I'm really weak on this sort of stuff though so I am almost certainly talking out of my arse.

Rock Hard Abs are just a sw-sw-swivel away!

: nope /nt by i (2.00 / 0) #11 Fri Dec 22, 2006 at 10:22:45 AM EST

[ Parent ]

Arse by TurboThy (2.00 / 0) #3 Fri Dec 22, 2006 at 09:19:54 AM EST

#DEFINE retun crash_horribly(true)
__
You can't fix anything, you can't change anything, so just tell them that everything is A. The Fuck OK. —Rogerborg

that would be cheating. by i (2.00 / 0) #14 Fri Dec 22, 2006 at 10:23:27 AM EST

me no cheating!

[ Parent ]

: Well by TurboThy (2.00 / 0) #15 Fri Dec 22, 2006 at 03:50:39 PM EST

What's the definition of retun then? ;)
__
You can't fix anything, you can't change anything, so just tell them that everything is A. The Fuck OK. —Rogerborg
[ Parent ]

man signal by lm (4.00 / 1) #4 Fri Dec 22, 2006 at 09:26:51 AM EST

blah, blah, blah, blah ... dividing the most negative integer by -1 may generate SIGFPE ... blah, blah, blah

There is no more degenerate kind of state than that in which the richest are supposed to be the best.
Cicero, The Republic

: bingo by i (2.00 / 0) #8 Fri Dec 22, 2006 at 10:18:42 AM EST

get a cookie (of the non-evil kind)

[ Parent ]

One reason by anonimouse (2.00 / 0) #6 Fri Dec 22, 2006 at 10:11:24 AM EST

Something divided by zero isn't necessarily zero; it tends to +/- infinity. Returning zero instead of handling the exception or ensuring the exception does not occur in the first place is bad practice.

Girls come and go but a mortgage is for 25 years -- JtL

: the function is nonsensical by i (2.00 / 0) #9 Fri Dec 22, 2006 at 10:20:24 AM EST

i could throw an exception instead of returning 0, but that's not the point.

[ Parent ]
: Not in integer maths. by ambrosen (2.00 / 0) #12 Fri Dec 22, 2006 at 10:22:52 AM EST

Undefined is a far better result to give. And what with no built in exception throwing, 0's the best invalid result available. Still, the essence of the question is whether 0's the only divisor that can cause an error. The answer is not.

[ Parent ]

thanks everyone who congratulated me with a new job | 15 comments (15 topical, 0 hidden) | Trackback


Make a new account
Username:
Password: