C programming tricks

While programming optimization that makes ones' code completely unreadable is often a bad thing, there are places for it, like that one inner loop of your code that takes up 98% of the program's running time.

What are you tricks for improving performance in C, other than the obvious inline assembly or the like?

>>60 is EXPERT QUALITY, except one thing:
2. ++i is faster than both i++ and i = i + 1.
This is actually quite true sometimes. In certain circumstances, a loop in GCC using while (++i <= j) will produce incl, cmpl, and jle instructions; whereas while (i++ < j) will result in movl, incl, cmpl, and jl. In this case, preincrementing shaves one full CPU instruction per loop iteration.