Comparing float value to zero

Questions & Answers
1

This code works as expected:

float myValue = 6.0f;

void Update()
{
  myValue -= Time.deltaTime;

  if(myValue < 0.0f)
    myValue = 0.0f;
}

public bool IsValueZero()
{
  return myValue == 0.0f;
}

But I’m curious if it’s safe to use a construction like that. I’m aware of float comparsion, but also wonder - can we do a safe float to value comparsion if we are sure that our float was set to exactly that value. It don’t have to be a zero, can also be something like:

float myValue = 6.43f;

if(myValue == 6.43f)
  Debug.Log("It's working!");

Will this construction always work as expected?

2

Yes. Setting a float directly to a value will not produce “rounding” errors. Checking if(x==4.0f), when you know it was directly set, is safe.

Setting a float to an int is always exactly that int (unless something like 345664345654.0, with too many significant digits.) Setting to a decimal will “round” the same both ways. So 6.43 may round to 6.42999, but it will always round the same way, so a direct compare is safe (but not commonly done.)

The only time “random” rounding occurs is when you do math. 0.1f10 may be 1.00001. But 0.05f20 may be 0.999999. The trick is, we know 1/3 is repeating 0.33333, so has to round. For computers, 0.1 is repeating, since it stores fractions as 1/2, 1/4, 1/8 … . So, 0.5 won’t round, and 0.5f*20 should be exactly 10 (but no one does stuff like that.)

Lerp, clamp, moveTowards, … will give an exact number. x=lerp(2.0f, 9.0f, percent); will give exactly 2.0 and 9.0 when percent is less than 0 or more than 1. Because, internally, they say “if percent 1 or more, value equals 2nd number.”