Comparison Efficiency

Question

What is generally faster:

if (num >= 10)

or:

if (!(num < 10))

Answer 1

Any decent compiler will optimize those two statements to exactly the same underlying code. In fact, it will most likely generate exactly the same code for:

if (!(!(!(!(!(!(!(num < 10))))))))

I would opt for the first of yours just because its intent seems much clearer (mildly clearer than your second choice, massively clearer than that monstrosity I posted above). I tend to think in terms of how I would read it. Think of the two sentences:

• if number is greater than or equal to ten.
• if it's not the case that number is less than ten.

I believe the first one to be clearer.

In fact, just testing with "gcc -s" to get the assembler output, both statements generate the following code:

cmpl $9,-8(%ebp) ; compare value with 9
jle .L3          ; branch if 9 or less.

I believe you're wasting your time looking at micro-optimisations like this - you'd be far more efficient looking at things like algorithm selection. There's likely to be a much greater return on investment there.