When Can You Safely Use `==` for Floating-Point Comparisons?

Floating-Point Comparison: When Does == Work?

The question arises from the potential for floating-point representations to introduce inaccuracies and inconsistencies. While it's widely acknowledged that floating-point comparisons can be problematic, there are specific scenarios where equality checks can be considered reliable.

Exact Floating-Point Representations

Yes, certain floating-point values, including whole numbers and 0.0, can be guaranteed to compare equal using ==. This is because the IEEE 754 standard ensures that integer values within a specific range are represented exactly as floating-point numbers.

Example:

float a = 1.0;
float b = 1.0;
a == b  // true

Cautions:

However, it's crucial to note that not all numerical values have exact floating-point representations. Calculations and conversions may introduce inaccuracies that can affect equality comparisons.

Comparison of Constants:

In the case of a call like foo(BAR), where both the function argument and the constant BAR refer to the same static constant, it is guaranteed that the comparison d == BAR will evaluate to true since they both reference the same exact floating-point representation.

Important Considerations:

• Assignment: Assigning whole numbers to floating-point variables is safe and will preserve exactness.
• Calculations: Arithmetic operations and conversions can introduce inaccuracies, potentially affecting equality checks.
• Special Cases: A limited subset of real numbers, such as powers of two, have exact floating-point representations.

Conclusion:

While floating-point comparisons are generally not recommended due to potential inaccuracies, there are specific cases where equality checks using == can be considered reliable. Whole numbers, including 0.0, have exact floating-point representations, and comparisons involving constants that reference the same value are guaranteed to be true. It's important to carefully evaluate the use of floating-point comparisons and ensure that they align with these criteria to avoid unexpected results.

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