Bad taste in programming [LWN.net]

Bad taste in programming

Posted Mar 1, 2007 17:14 UTC (Thu) by pr1268 (subscriber, #24648)
In reply to: Some idle comments about Linus' e-mail response and Linux by ekj
Parent article: Re: [GIT PATCH] HID and USB HID update for 2.6.21-rc2

Thanks to the above posters for your responses.... But I was thinking more low-level bad taste in kernel programming. ;-) As in:

/* New kernel idle loop */
for(;;);
if(something->uid = 0)
/* Hopefully no one will notice missing '=' */
if(x != x)
/* How come this code never gets executed? */
while(!((!x)&&(y->a!=3))||(y->b<=y->c->d->e())&&z->f())
/* Someone tell me this while condition is easy to read */
...

But I suppose bad taste can exist at all levels of programming.

Disclaimer: I am easily entertained by browsing code at the IOCCC Web site, but I whole-heartedly agree that it's absolutely no fun having to maintain sloppy code whose author exhibited bad taste.

As for coding style (indentation, proper use of curly braces, etc.), Robert Love's book has some style guidelines for kernel code in one of the appendices. Not that I'm trying to plug his book or anything (but it is a decent read).

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Bad taste in programming

Posted Mar 2, 2007 16:57 UTC (Fri) by kleptog (subscriber, #1183) [Link]

Actually, I like for(;;) because I find it stands out and looks better than while(1).

Bad taste in programming

Posted Mar 2, 2007 18:48 UTC (Fri) by wcooley (guest, #1233) [Link]

Sure, but the code in question wasn't "for(;;)"--it was "for(;;);"--a subtle but huge difference.

Infinite loops as bad taste

Posted Mar 3, 2007 1:20 UTC (Sat) by pr1268 (subscriber, #24648) [Link]

Actually, I was taught that for(;;) is faster than while(1) since the former doesn't need to perform a logical evaluation, but the latter does. (Wouldn't this be a weird flame war debate?) I'm since convinced that this is old news, since my experiences hacking some C/C++ code with gcc -S and gcc -c show identical .s and .o files in either case (optimized or not).

I recently coded a loop as for(;;i++) { /* ... */ } (don't ask). :^)

Infinite loops as bad taste

Posted Mar 5, 2007 6:15 UTC (Mon) by landley (guest, #6789) [Link]

> Actually, I was taught that for(;;) is faster than while(1)

And circa 1984, this was true.

Compilers change. Optimizers change. Hardware changes drastically. (2
megabytes of L2 cache?)

x=5;
if (blah) x=7;

This is now generally faster than:
if (blah) x=7;
else x=5;

Why? Branch prediction with conditional assignments to avoid bubbles in
the pipeline. Taking a branch is noticeably slower than doing an extra
(unnecessary) assignment, and the if/else means _either_ way you branch.

However, 90% of the time you don't have to _care_ because your compiler
knows about conditional assignment and will rewrite variant #2 to look
like variant #1.

And if you religiously write #1 it's possible that in 5 years new hardware
will show up that makes the _previous_ way of doing it the fast way again.
(Once upon a time, rotating a point around a circle, programmers
precalculated a lookup table of all 360 positions to avoid doing slow
trigonometry math. Then processors got a clock multiplier faster than the
motherboard, and the lookup table became slower than doing the math
because it didn't fit in cache. Then caches got big again, and the lookup
table fit in memory again... It's a pendulum. There IS no one right
answer. Even if you know _everything_ the compiler is doing, if your code
is any good it could easily outlive that specific processor and compiler
version. (And if it isn't any good, what's the point in trying to
optimize it?)

Remember Ken Thompson's "When it doubt, use brute force" because it's darn
good advice.

That said, I use for(;;) because I think it's cleaner. (It lies to the
compiler slightly less; while(1) smells like if(1), and even though both
tests get optimized out I don't like having it there without a reason.)