C# mod fails in Unity 3D

Question

I am performing the following, but instead of zRem having the expected value of zero I get 2.384186E-07:

Vector3 t = this.transform.position - _startPosition;
float xRem = t.x % 1;
float zRem = t.z % 1;

In this instance:

this.transform.position = 2.5, 0, 3.5
_startPosition = 1.5, 0, 1.5

xRem is correct, but zRem have the value 2.384186E-07.

Any suggestions on how to fix this?

UPDATE #1 : When using the values above it should not enter this block, but because of zRem it does.

if(!Mathf.Approximately(xRem, 0f) || !Mathf.Approximately(zRem, 0f))
{
     return;
}

Answer 1

Well, mod is not failing... Float point arithmetics always involve some level of precision/error.

I know, Mathf.Aproximately is meant to take ilthis into account, but Unity have its own Epsilon value for comparing floats and, guess what, it's value isn't documented.

https://docs.unity3d.com/ScriptReference/Mathf.Epsilon.html

(Maybe it is system dependent, according to the representation model of float values. Maybe it's IEEE conformant, I don't know)

Thing is: you should define what threshold use that conforms with your game logic, something like this:

if(xRem <= threshold)

Or

if(Mathf.abs(xRem) <= threshold)