Unity / RIDER: order of multiplication operations is inefficient?

问题

The rider IDE is informing me that the following is inefficient

        transform.Translate(moveDirection * speed * Time.smoothDeltaTime);

and wants to re-write it as

        transform.Translate(Time.smoothDeltaTime * speed * moveDirection);

Anybody know why ?

Its all multiplications, whats the difference ?

For some context, here is the value of speed and moveDirection

private Vector3 moveDirection = Vector3.left;

private float speed = 2.5f;

I am little confused in understanding why its better ?

Can anyone help?

Thanks

回答1:

Vector3 has 3 components. X, Y and Z.

Multiplying a Vector3 by a value multiplies the components by that value.

Since there are 2 values beside the vector, order matters not for the result, but does for the number of operations.

That is because vector-first will result in 3+3=6 multiplications:

1. X*=speed
2. Y*=speed
3. Z*=speed
4. X*=time
5. Y*=time
6. Z*=time

While vector-last will be 1+3=4 multiplications:

1. scale=speed*time
2. X*=scale
3. Y*=scale
4. Z*=scale

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Either way, it's just Rider being paranoid about performance, and that level of optimization, while welcome, is definitely not required.

来源：https://stackoverflow.com/questions/57933831/unity-rider-order-of-multiplication-operations-is-inefficient