Slashdot Mirror
Pet Bugs?
benreece asks: "During my few years as a programmer/developer I've come across some strange bugs. Recently I found that Microsoft's VB/VBScript(ASP) round function has problems (for example, 'round(82.845)' returns '82.84' instead of '82.85'). It took me an annoyingly long time to realize the problem wasn't mine. I'm wondering what other obscure, weird, and especially annoying bugs in languages/compilers/etc have frustrated other developers." Memorable bugs. Every developer has one. What were yours?
Round to the nearest even digit if the truncated value is .5 Otherwise there's a slight upward bias.
Infuriate left and right
You know the kind. When you add in debug they go away.
We have a spider that comes crawling around our cubes every now and then. We don't kill him, figuring he helps keep the other bug populations inside down. We call him our little web developer.
I'm serious.
-Pete
Soccer Goal Plans
I worked a wicked long time ago on the HotJava browser, and we were forever running into strange behaviors in the ways IE and Netscape handled what looked like normal HTML tags.
My favorite was a bug we saw with a three column table. The table's three cells were specified like this:
<td width="31"></td><td width="42></td><td width="29"></td>
Being a good little HTML-compliant browser, HotJava displayed them with those pixel widths. But lo and behold! When displayed in Netscape, the table filled the screen.
We bashed our heads against the wall to figure this out until we realized that the numbers added up to almost, but not quite, 100. Netscape was treating them as percentages rather than pixel widths, even though they lacked percent signs. The cutoff turned out to be somewhere around 104 to 96. Anywhere in there and the browser would assume percentages.
-- What is this Earth thing you call "slow"?
this has to be the most memorable one.
it's in the Linux man file
BUGS
Never use this function. This function modifies its first argument. The identity of the delimiting character is lost. This function cannot be used on constant strings.
When I go to the front page I see one set of topics. If I go to "older stuff" I see a few topics there that seem like they should be on the front page, but aren't. I haven't checked any boxes under the preferences page's "Exclude stories from home page" so I would think they would all show up.
I know this must be happening for most Slashdot readers because the topics I don't see have maybe a dozen posts after a day. So is it happening to you too?
I just observed this bug a while ago while porting some software to windows. Do the following:
fopen some file for writing.
write some stuff.
fseek to some offset near the beginning.
write some more stuff.
fclose.
Simple right? Wrong. I observed that the second write didn't get performed unless you explicitly do a fflush before the close. Imagine, not writing dirty buffers out on a fclose....unbelievable.
In Soviet Russia, hot grits put YOU down THEIR pants.
Just to show how cool I am.
Way back when, I worked for a company that produced a special version of SysV Unix. One of our developers was going through all the source code and looking for places where global variables were initialized to zero, thusly:
int x = 0;
and changing them to be implicit:
int x;
This had the effect of reducing the size of the data section of the binary and moved the variable to the BSS section. A simple and safe optimization, albeit somewhat anal.
Shortly thereafter things started acting funny. The OS would slowly go crazy in very subtle ways after booting. It was not clear what was wrong or if anything actually was wrong, and nobody connected the variable initialization change to the problems with the kernel. After something like 3 months, they finally figured out that when this change was applied to a single variable in the C library it invoked a compiler bug that caused the library to be compiled in such a way that caused the kernel to fail to reset the CPU's floating point registers during a context switch. (How a faulty C library could cause the kernel to do this is still a mystery to me.) This is one of the weirdest bugs I've experienced, though I'm not doing it justice here due to fading memory.
This was a major issue, because when the interrupt was lost the system froze up and had to be rebooted (this is an embedded app - not a desktop).
I offered to assist the engineer responsible for this code. We spent two days tracing the problem in extreme detail, checking and cross-checking our results. We both concluded that the processor was simply "losing" the interrupt. There was no rational explanation. We adopted the countermeasure of using a fine grain watchdog timer to look for the lost interrupt. This isn't the best solution, since what was to keep the watchdog interrupt from being lost??? But it was the best we could do. And it worked.
The project lead, however, was very unhappy with our solution. He was convinced that we had overlooked the cause of the problem, which had to be software-based. I countered that, though he could certainly be right, it would be better to leave the watchdog in and let the project move ahead until we stumbled across the real cause in due time. He reluctantly accepted this approach.
My vindication took five months, but what sweet irony when it did. It turned out that some other company, which also used the 54X chip, had encountered the same problem, but they figured it out (and I'll never know how). The problem was that the 54X (at that time) had a silicon flaw that, when certain integer rounding instructions executed at the same instant that an interrupt were being asserted, the interrupt could be "lost". This was confirmed by TI to be a silicon fault, and no amount of software handstands or cartwheels could fix it. The only workaround was to not use those rounding instructions!
OK- top that....
My all-time favourite bug is in the microcode of the 6502/6510...
:o)
An indirect jump where the source address was on a page boundary caused the high-byte to be pulled from the beginning of the current page, instead of the beginning of the next page..
eg.
$0100 holds $80
$01FF holds $32
$0200 holds $14
then the command
JMP ($01FF)
would load the program counter with $8032, instead of $1432
First time I saw it used was in some copy-protection code in the C64 version of Sim City.. It was some obfusication to screw up beginning crackers.. (it threw me for about 5 minutes..)
Ahh, those were the days
The buttons below were pretty cool too. One said "ok" and the other one said "lame!"
If you clicked the lame! button, you just got to fill out a little comment card, but the feature cracked me up the first couple times I saw it.
I once worked on a DOS app (about 10 years ago) that had a very strange bug. The system would lock up for no reason we could figure out. The offending statement was a printf that printed one single character (a control-G) to the screen to make it beep.
After some testing on different computers, we discovered that it only crashed on machines with an AMI bios. Phoenix BIOS machines worked just fine, and so did real IBM machines. We never digged into the BIOS code to figure out what the problem was, but we mentioned it to the Phar Lap support people (those people were the smartest support people I ever ran across). They told us that they knew about the bug, and even explained what was happening inside the bios to make it crash the machine, but it's been 10 years so I don't remember the details anymore.
If tits were wings it'd be flying around.
As far as I could tell when I was using Perl, running under strict mode would make it so that print() only worked with strings that ended in \n. I can't tell you how long that takes every beginning Perl programmer to figure out. Took me a good four hours.
My favorite bug in slashcode is that clicking "Parent" in my default story view always returns the default story view, not the parent of the post I'm clicking on. So I have to click on the post ID number, then click parent on the resulting page.
There are no trails. There are no trees out here.
I remember discovering __LINE__ and __FILE__ when I was doing some perl debugging. It was handy to do stuff like:
do(something()) or die("Failed on line " . __LINE__);
Of course, then I had this idea of using a debugging function (this is before I knew of warn,croak,carp, et al). So I happily wrote my function
sub debug { die("Failed on line " . __LINE__); }
And then spent hours trying to figure out why my code always failed on line 78, which happened to be where the debug() function lived. D'oh!
ID-10-T is a way of life
It's turn-back-the-clock time, boys and girls. Remember all of those DOS calls? It was interrupt 20, wasn't it? Remember the findfirst and findnext functions that would get you a list of the files in a directory? You could give findfirst a list of attributes and a filespec, and it would give you a file that matched it (findnext just repeated the last findfirst). Valid attributes to pass were the archive flag, read-only, directory, etc. Except the directory one didn't work! It was simply ignored, so you had to sort out what files were directories or not yourself. What a pain in the ass! And did they ever fix it? I'll give you one guess.
Oh, and I can't mention old MS bugs without mentioning MASM vs TASM (just because it illuistrates why Borland is so cool and MS is not). Back in the day, when applications were coded in assembler, MASM (Microsoft Macro Assembler) was popular as hell. Borland, though, came out with Turbo Assembler, which had a better syntax (optionally), could assemble MASM syntax faster than MASM could, and could emulate all the bugs in the different versions of MASM. Ah.
Well, that's enough MS bashing for me today (or maybe just this hour...).
What's next - random() always returning 666 no matter what seed you use?
random() only returns 666 if you use a demon seed!
cpeterso
Back in the day when I used to program in C++, I was also really into making little ascii-art comments in my code. One time I had some code that looked like this:
#include <stdio.h>
// tom 7 was here - 1998 \\
typedef unsigned char uchar;
int something(uchar c);
...
(In actuality, the code was longer and more complicated, so it wasn't so easy to figure out...). Can you see the bug?
As others have noted, this isn't a bug, these are just the stories that the editors decided weren't important enough to warrant a full front-page thing. Funnily enough, these "section page only" articles tend to have much better and more insightful comments than the front page articles, because people only post there if they really care :)
:( Unless i'm just confused about how it's done, anyway. But it seems to be disabled, going to a non-existent sid now shows "Nothing for you to see here, move along".
Beyond that, though, what i liked was that used to, on slashdot, you could post to sid's that didn't exist. Like, you could go to http://slashdot.org/article.pl?sid=haiku, or something, and while there wouldn't be a story at the top of the page, you could post comments there, and the next person to go to http://slashdot.org/article.pl?sid=haiku would see that comment and could reply to it, until the comment reached a certain age and was automatically deleted. There used to be a whole bunch of these little "hidden" discussion areas littered all over slashdot that people would form entire little communities around them. Unfortunately, this was mostly used for troll groups to coordinate attacks. (K-9-something-inches or something? I don't remember.)
Unfortunately they seem to have removed this feature from slashdot
There were some other really bizarre but fun slashdot bugs, like how there was some wierd twilight zone area at sid 0, or sid null (or something.. "slashdot.org/?sid=", i think was the url.. i can't remember. i think it was called "test discussion". or something) that you'd sometimes get dumped at if you clicked on the "parent" link in the preview of a post you were writing. Not always, just sometimes. The thing was though, there was some other bug that for some unfathomable reason would sometimes cause posts to get moved out of their correct threads, and into the null discussion, at random. And people wouldn't notice this. And so if you went to the test discussion, you'd just see hundreds and hundreds of random posts, totally irrelivant to each other or anything else, on totally random subjects. It was fun to go through this and try to guess what subjects the posts were on.
And then there was.. i barely even remember this one. There was a page i managed to get to a couple times-- i can't remember how, but there was a simple way to do it that would work every time-- that just said, "Here are some open discussions", and linked a bunch of articles. The Test Discussion was always near the top of this list. I'd expect that whatever this page is, it's gone now, but can anyone remember what this page was or how i would have gotten to it?
Irritable, left-wing and possibly humorous bumper stickers and t-shirts
I was trying to debug a CMOS standard-cell chip that I designed in the late 80's. The bug was elusive, only showing up occasionally and I'd written various test routines to ferret it out. I started to suspect it was something to do with the PCB layout, so I was cutting and pasting tracks. Suddenly all the test routines worked perfectly and I thought GOTCHA! My mind was almost blown when I realized that I had inadvertently cut the power trace to the chip - it was working perfectly when Vcc wasn't connected!
Of course, I eventually figured out that the original problem was ground bounce and that with Vcc disconnected, the chip was getting power through the protection diodes on the control lines and bus. The lower voltage was slowing down the edges and reducing the ground bounce so that it worked correctly. I eventually solved the problem with PCB layout changes and the chip started working with Vcc connected!
Look, it's trying to think - Albert Rosenfield
There is no "proper" way to reduce the precision of a number under all circumstances. Each method of rounding or truncating 0.5 has its own pitfalls:
So, as you can see, there's no right way per se. It just depends on what you're doing.
--JoeProgram Intellivision!
If they had a sense of humour, they would have shipped version 1.0999999.
Accountability on the heads of the powerful.
Power in the hands of the accountable.
random() only returns 666 if you use a demon seed!
My favorite "bugs" are the truly horrible random number functions in almost every single language library on earth. They're usually linear congruential generators: fast, but utterly useless for any work that requires serious "randomness" such as Monte Carlo simulations. They have very short recurrence times, strong sequential correlation, etc.
Back in grad school, I had to substitute the Knuth ran3 routine for the supplied C library functions in both gcc and xlc since they were just awful.
Fast forward 8 years. I made the stupid assumption that since Java was a new language and that horrible problems with random number generators were well known that Sun would actually provide a decent RNG. Nope: just as badly flawed as the C one.
I suspect this is simply something to give up tilting at windmills about: random() is good enough for simple games and anyone doing real work knows to stay the hell away.
"Seven Deadly Sins? I thought it was a to-do list!"
A common problem was that the heads on the hard drive would get stuck, and the machine would cease to operate. The standard operating procedure to remedy this was told to me as:
If that didn't work, secondary protocol was to remove the hard drive from the machine, place it on the desk, and hit it three or four times with the blunt end of a screwdriver.
According to the techs, this worked about 90% of the time.
Still, with a plan, you only get the best you can imagine. I'd always hoped for something better than that. -CP
There are implementations in C, Java, PHP, Fortran, Excel (I assume VBA) and probably others.
I only have experience with the Java impl, and it is very good. There are two classes, MersenneTwister, which is a true descendant of java.util.Random, and there is also a MersenneTwisterFast class, which does NOT inherit from Random (same public methods, and identical algorithm though), but clocks in at about twice the speed, due to tricks like avoidance of synchronization, and method inlining and finalizing.
"Mind, as manifested by the capacity to make choices, is to some extent present in every electron." -Freeman Dyson
An infinte loop isn't quite as elegant as a single statement that wreaks havoc on your system, but it's still simple enough. In order to generate the "desired" result, you have to backspace beyond the first character of the terminal window, then output a printing character to the left of the beginning of the buffer. Apparently cmd.exe doesn't check for this condition, and triggers an error in a system-critical process.
I remember Microsoft bragging about how DOS programs run in their own virtual machine, so a mis-behaved DOS app can't crash your computer. I think this example here is proof-positive to the contrary.
If anybody has any more technical information about the cause (and possibly history) if this bug, I'd love to hear it.
What's it do? Oh, yeah, it reboots your computer. No shutdown, no warning. Just like hitting the power switch.
And aren't you glad you paid over $1000 for MS server software that can be rebooted by any user who executes a 4-character printf?
"With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea...."
RFC 1925