How to Avoid Floating Point Errors When Using rad2deg

In PHP, the rad2deg() function seems straightforward, but floating-point errors may lead to some subtle issues in real-world calculations.

Sources of Floating Point Errors

Floating point numbers cannot represent all decimals precisely in a computer; they typically only approximate a value. This means:

echo rad2deg(pi()); // Expected 180, but might result in 179.99999999999997

Such small errors can cause logical issues when comparing angles or performing conditional checks.

How to Prevent Problems Caused by Floating Point Errors

1. Use Rounding: When precise integer angles are needed, use round():

$degrees = round(rad2deg(pi())); // Result is 180
    

<li><strong>Use Tolerance Comparisons:</strong> Don't directly compare floating-point numbers with equality. Instead, use a range that allows for some error:</li>
<pre>

$epsilon = 0.00001;
if (abs(rad2deg(pi()) - 180) < $epsilon) {
echo 'Close to 180 degrees';
}


<li><strong>Keep Calculations in Radians, Convert Later:</strong> If possible, perform all math in radians and only convert to degrees when displaying the result:</li>
<pre>

$angleRad = pi() / 4;
$resultRad = sin($angleRad) + cos($angleRad);
$resultDeg = rad2deg($angleRad); // Convert last

Conclusion

While floating point errors are unavoidable when using rad2deg(), they can be effectively mitigated through rounding, tolerance comparisons, or delayed conversions. Proper handling of floating point numbers is crucial for ensuring the accuracy of mathematical computations.