在 sqrt 之前添加距离条件是否会提高此代码的性能？

Question

Let me pose a hypothetical question. Given these two blocks of C# code, is the second version faster? I've researched and tested/timed this quite a bit and I have my own theory (which I will keep to myself for now to not influence the answers), but I want to ask the question here to keep my own biases in check. The reason why I'm studying this is because it was asked in an interview question recently, and I'm not satisfied with how the result was discussed. Thank you in advance.

First version:

public float DistanceBetweenPoints(float x1, float y1, float x2, float y2)
{
    float result;
    float xDifference = Math.Abs(x1 - x2);
    float yDifference = Math.Abs(y1 - y2);
    result = (float) Math.Sqrt(xDifference * xDifference + yDifference * yDifference);
    return result;
}

Second version:

public float DistanceBetweenPoints(float x1, float y1, float x2, float y2)
{
    float result;
    float xDifference = Math.Abs(x1 - x2);
    float yDifference = Math.Abs(y1 - y2);

    if(xDifference > 0 || yDifference > 0)
    {
        result = (float) Math.Sqrt(xDifference * xDifference + yDifference * yDifference);
    }
    else
    {
        result = 0;
    }

    return result;
}

I'm specifically wondering if adding in the 0 distance check is an optimization. At this point, I'm going to give more context around this question. The first version was what I had submitted for a solution, and the second version was what the interviewer had insisted that I do to make the code more performant. Their claim was that the second version is up to 20 times faster than the original, but I highly disagree. If this was possible, then you can bet that Microsoft would have included that optimization within the Sqrt call itself. Not only that, but from my understanding, the call is usually implemented via hardware, and when I measured the timing of it, I was seeing about 4-5 ticks per call. It shows the same results with the "optimization" of the 0 distance check. That's very impressive, and I don't know if there is anything I can do to make it faster.

Answer 1

As usual, instead of trying to fix "broken" framework code, you should be trying to fix your own broken algorithms. Because if there was a way to make Math.Sqrt faster, it would already be done.

Specifically for distances, chances are you don't need to actually calculate the distance, the squared distance suffices (or again, fix your algorithm to make it suffice). That means you can drop the Math.Sqrt call completely!