CODEWITHSUNDEEP
c#booleanvariable-assignment
Francesco Belladonna
Francesco Belladonna

Reputation: 11689

Faster assignment or check for bool values

The question is simple, which is faster between CalledOften1 and CalledOften2

    class MyTest
    {
        public bool test = false;
        void CalledOften1()
        {
            if (!test) test = true;
            DoSomething();
        }
        void CalledOften2()
        {
            test = true;
            DoSomething();
        }
    }

Is the compiler optimized (if possible) to avoid future assignments of test if it's already true?

UPDATE: This question is just an information, I will not use the if (bla) style if I can write test=true, I prefer code readability.

Upvotes: 2

Views: 4862

Answers (6)

Mud
Mud

Reputation: 28991

Premature optimization is the root of all evil. Use the one that expresses your intent most clearly.

(I'm guessing a read+branch is going to be more expensive than just a write, but don't really know the CLR. The important thing is that computers are increasing in speed exponentially, and programmers aren't. Algorithmic improvements in performance bottlenecks are worth exploring, barely measurable constant-time improvements for their own sake aren't.)

Upvotes: -4

Mark Byers
Mark Byers

Reputation: 838256

I prefer to measure for these sorts of questions rather than guess:

  • CalledOften1: 52 million operations per second
  • CalledOften2: 53 million operations per second

So they are nearly the same. If anything, the simpler method is also the faster.

Upvotes: 8

Jon Skeet
Jon Skeet

Reputation: 1500665

I would expect the second version to be slightly faster, given that it doesn't involve any branching. It also expresses the intention of "make sure the variable is true, whatever it was before" more clearly IMO. However:

  • I doubt that it's significant
  • Any number of actual changes in context could make the results change (including your code, or the version of the framework you're running against)
  • Write the clearest code first, and optimize later
  • Benchmark this against your real code, under realistic conditions before you decide to change anything

Upvotes: 3

Reed Copsey
Reed Copsey

Reputation: 564413

This is a perfect example of premature optimization.

If you want to set test to true every time, just set it. Don't complicate your code for a theorized speedup.

That being said, the reduced instruction set of the second example, along with being simpler and more maintainable, is most likely faster due to avoiding the branching and reducing the number of instructions. A single assignment of a bool is a very fast operation. If you really need to know how much faster it may be, I would profile this yourself. However, I suspect that either would be fast enough in any case.

Upvotes: 2

Brian Ball
Brian Ball

Reputation: 12596

If I had to guess, I would say that CalledOften2 is more optimized, as there is no logic test operation done.

In the end, if you are looking at this level of optimization, then your application will probably go as fast as it can. Any performance gain you get out of this type of optimization will likely never be noticed by anyone.

My two cents, Brian

Upvotes: 1

Andrey
Andrey

Reputation: 60065

Compiler optimizes only something that is definite at compile time. This is changed at runtime so answer is no. Compiler could optimize if you were checking against constant. CalledOften1 is faster, but the magnitude is so small that you would not notice. This is kind of microptimisation you should avoid.

Upvotes: 1

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