When to use Fixed Point these days

Question

For intense number-crunching i'm considering using fixed point instead of floating point. Of course it'll matter how many bytes the fixed point type is in size, on what CPU it'll be running on, if i can use (for Intel) the MMX or SSE or whatever new things come up...

I'm wondering if these days when floating point runs faster than ever, is it ever worth considering fixed point? Are there general rules of thumb where we can say it'll matter by more than a few percent? What is the overview from 35,000 feet of numerical performance? (BTW, i'm assuming a general CPU as found in most computers, not DSP or specialized embedded systems.)

Answer 1

Use fixed-point when the hardware doesn't support floating-point or the hardware implementation sucks.

Also beware when making classes for it. Something you think would be quick could actually turn out to be a dog when it comes to profiling due to (un)necessary copies of classes. That is another question for another time however.