Detecting and adjusting for negative zero

Question

I have some code that has been port from Java to C++ ``` // since this point is a vector from (0,0,0), we can just take the // dot product and compare double r = point.dot(normal); return (r>=0.0); ``` But in C++ `r` can be either `+0.0` or `-0.0`, when `r` equals `-0.0` it fails the check. I've tried to adjust for negative zero in the code below but it never hits the DEBUG("Negative zero") line. But `r2` does print out equal to `+0.0`. ``` // since this point is a vector from (0,0,0), we can just take the // dot product and compare double r = point.dot(normal); if (std::signbit(r)){ double r2 = r*-1; DEBUG("r=%f r=%f", r,r2); if (r2==0.0) { DEBUG("Negative zero"); r = 0.0; //Handle negative zero } } return (r>=0.0); ``` Any suggestion? TESTING CODE: ``` DEBUG("point=%s", point.toString().c_str()); DEBUG("normal=%s", normal->toString().c_str()); double r = point.dot(normal); DEBUG("r=%f", r); bool b = (r>=0.0); DEBUG("b=%u", b); ``` TESTING RESULTS: ``` DEBUG - point=Vector3D[ x=1,y=0…

Accepted Answer

Well, a generic suggestion when using `double`s is remembering they are not exact. Thus, if equality is important - using some tolerance factor is usually advised.

In your case:

```
if (|r - 0.0| >= EPSILON)
```

where `EPSILON` is your tolerance factor, will yield true if `r` is not 0.0, with at least `EPSILON` interval.

Detecting and adjusting for negative zero

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