CODEWITHSUNDEEP
c#compiler-optimization
Fr4nz
Fr4nz

Reputation: 1636

Will C# compiler optimize this operation inside a loop?

What is the best approach between the code below where verticesInnerSides.Length / 2 is written in it's complete form each time :

for (int i = 0; i < verticesRoof.Length; i++) {
    verticesInnerSides[i * NB_VERTICES + verticesInnerSides.Length / 2] = startInside;
    verticesInnerSides[i * NB_VERTICES + verticesInnerSides.Length / 2 + 1] = startInside + Vector3.up * HEIGHT_ROOF;
    verticesInnerSides[i * NB_VERTICES + verticesInnerSides.Length / 2 + 2] = endInside;
    verticesInnerSides[i * NB_VERTICES + verticesInnerSides.Length / 2 + 3] = endInside + Vector3.up * HEIGHT_ROOF;
}

Or the following where it's written outside the loop once :

myCalculatedVar = verticesInnerSides.Length / 2;
for (int i = 0; i < verticesRoof.Length; i++) {
    verticesInnerSides[i * NB_VERTICES + myCalculatedVar] = startInside;
    verticesInnerSides[i * NB_VERTICES + myCalculatedVar + 1] = startInside + Vector3.up * HEIGHT_ROOF;
    verticesInnerSides[i * NB_VERTICES + myCalculatedVar + 2] = endInside;
    verticesInnerSides[i * NB_VERTICES + myCalculatedVar + 3] = endInside + Vector3.up * HEIGHT_ROOF;
}

Will C# compiler optimize this operation in the first case ?

Upvotes: 1

Views: 152

Answers (2)

Ivan Kochurkin
Ivan Kochurkin

Reputation: 4501

In my opinion the best way to reach readability and performance is:

myCalculatedVar = verticesInnerSides.Length / 2;
for (int i = 0; i < verticesRoof.Length; i++) {
    int ind = i * NB_VERTICES + myCalculatedVar;
    verticesInnerSides[ind] = startInside;
    verticesInnerSides[ind + 1] = startInside + Vector3.up * HEIGHT_ROOF;
    verticesInnerSides[ind + 2] = endInside;
    verticesInnerSides[ind + 3] = endInside + Vector3.up * HEIGHT_ROOF;
}

But you can waste your time and write some benchmarks test for testing this piece. I am sure that if a bottleneck will exist it will be in another place in the code.

Upvotes: 1

Noctis
Noctis

Reputation: 11773

  1. Why would you do it like the first code example to begin with ? The second one (without looking at the compiler) seems more efficient.

  2. As per Code Complete, and many other suggestions: Don't optimize if you don't need to.

  3. If you need to, simply benchmark. (There's plenty of threads, blogs and answers about what to look out for when benchmarking, but I'm sure you'll be able to find them :)

As an extra bonus, here's another answer with all the links you'll need :)

Upvotes: 1

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