Performance anti patterns

Question

I am currently working for a client who are petrified of changing lousy un-testable and un-maintainable code because of \"performance reasons\". It is clear t

Answer 1

1. Using #defines instead of functions to avoid the penalty of a function call. I've seen code where expansions of defines turned out to generate huge and really slow code. Of course it was impossible to debug as well. Inline functions is the way to do this, but they should be used with care as well.

2. I've seen code where independent tests has been converted into bits in a word that can be used in a switch statement. Switch can be really fast, but when people turn a series of independent tests into a bitmask and starts writing some 256 optimized special cases they'd better have a very good benchmark proving that this gives a performance gain. It's really a pain from maintenance point of view and treating the different tests independently makes the code much smaller which is also important for performance.