How dangerous is it to compare floating point values?

How Dangerous is it to Compare Floating Point Values? 😱

The Issue 😕

You're working with UIKit, using CGFloat to handle resolution-independent coordinate systems. But when you need to check if a value is equal to another, like frame.origin.x == 0, it makes you feel sick 😷. You're worried that comparing floating point values using ==, <=, >=, <, and > could be risky because of the imprecision of floating point numbers.

The Unprecision Problem 🤔

You're absolutely right! Floating point numbers, like CGFloat, can have precision issues. For example, a seemingly simple value like 0 might actually be represented as 0.0000000000041. When comparing floating point values, you need to be aware of this potential imprecision.

Handling Comparison in Objective-C 🔍

Now, let's get to the important part: how does Objective-C handle comparisons with floating point values?

In Objective-C, comparing floating point values with ==, <=, >=, <, and > can indeed encounter issues due to imprecision, resulting in false positives. This means that even if origin.x appears to be 0, it may not compare to 0 as true.

The Safe Approach to Comparing Floating Point Values ✅

To overcome this precision issue when comparing floating point values, you can use a technique known as epsilon comparison. 🧪

Epsilon comparison involves defining a small range of acceptable values around the target value, within which the comparison will be considered true. Here's an example:

#define EPSILON 0.000001

if (fabs(theView.frame.origin.x - 0) < EPSILON) {
    // do important operation
}

In this example, we define EPSILON as 0.000001 to create a small allowable deviation from the target value of 0. By taking the absolute difference between the two values using fabs(), we can ensure that any differences within the defined epsilon range will be considered equal.

Your Call-to-Action 📣

Floating point comparisons can be treacherous 😱, but now that you know the safe approach, it's time to take action! Start applying the epsilon comparison technique today and prevent false positives in your code. Share this blog post with your fellow developers 🤗, and let's spread the word about safer floating point value comparisons!

What are your experiences with comparing floating point values? Have you encountered any challenges or found alternative solutions? Let's continue the conversation in the comments below! 💬👇