If statement processing speed

Question

This is something simply to ease my curiosity, if someone would feel like answering it though that would be fantastic.

With if statements, is the time taken to calculate the result affected by the way it's written?

So what I mean is (if that wasn't overly clear) would the following two statements take the same amount of time to process?

if 1 < 2 and 3 = 3 then
   //do something
end if

compared to

if 1 < 2 then
    if 3 = 3 then
      //Do something
    end if
end if

I'm not sure why this has the java and the .net tag to be honest. — Austin, Nov 13 '12 at 06:03
The questions wasn't language specific, so I put it under the two categories I know. Was just out of curiosity. — Lift, Nov 13 '12 at 06:05

score 4 · Accepted Answer · answered Nov 13 '12 at 06:06

4

If we consider that the compiler will not optimize these two calls, then the second statement will require two branching instructions instead of one. And branching requires some extra work for the CPU because of pipelining. So, technically, the second version will require more work, but it should not matter here.

answered Nov 13 '12 at 06:06

Denis Tulskiy

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Cool, thanks! If you don't mind answering another questions, do languages such as Java and .net optimize such things? – Lift Nov 13 '12 at 06:09
@Feash: Java optimizer is pretty smart, but I can't tell you exactly whether it will optimize nested ifs or not. It probably will. – Denis Tulskiy Nov 13 '12 at 06:12
1

Naively the first one would require two branches as well, because of short-circuiting. – harold Nov 13 '12 at 11:41
@harold: hmm, didn't think about it. Then both cases are equivalent. Thanks. – Denis Tulskiy Nov 13 '12 at 15:34
There's no branch in this case. – Aki Suihkonen Nov 13 '12 at 16:33
@AkiSuihkonen: could you please explain why there would be no branch? – Denis Tulskiy Nov 13 '12 at 17:27
This case reduces to if(true) if (true) { }; or if (true && true) and finally just to the statement: { }. – Aki Suihkonen Nov 13 '12 at 17:29
1

@AkiSuihkonen that's only if the compiler does some optimizations and the constants 1, 2 and 3 are *not* meant to be placeholders, and that would just defeat the whole question. – harold Nov 14 '12 at 11:25

score 3 · Answer 2 · edited May 23 '17 at 11:52

3

This is just another case of premature-optimization. You are not going to gain anything by thinking a lot about this.

What you should be focusing on is how to make your code more readable.

edited May 23 '17 at 11:52

Community

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answered Nov 13 '12 at 06:04

Bhesh Gurung

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If you're not answering the question, you should post a comment, not an answer. – Bad Request Oct 20 '15 at 21:19

If statement processing speed

2 Answers2