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Problems can arise when the programmer uses such operators on NaN values in comparison operations. There is also a possibility that the input validation condition does not expect a NaN value as input.

Noncompliant Code Example

A frequently encountered mistake is the doomed comparison with NaN, typically in expressions. As per its semantics, no value (including NaN itself) can be compared to NaN using common operators. This noncompliant code example demonstrates one of the many violations.

public class NaNComparison {
  public static void main(String[] args) {
    double x = 0.0;
    double result = Math.cos(1/x); // returns NaN if input is infinity
    if(result == Double.NaN) { // compare with infinity
      System.out.println("Both are equal");
    }
  }
}

Compliant Solution

This compliant solution uses the method Double.isNaN() to check if the expression corresponds to a NaN value.

public class NaNComparison {
  public static void main(String[] args) {
    double x = 0.0;	  
    double result = Math.cos(1/x); // returns NaN if input is infinity
    if(Double.isNaN(result)) { 
      System.out.println("Both are equal");
    }
  }
}

Risk Assessment

Comparisons with NaN values may lead to unexpected results.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

\[[JLS 05|AA. Java References#JLS 05]\] [Section 4.2.3, Floating-Point Types, Formats, and Values|http://java.sun.com/docs/books/jls/third_edition/html/typesValues.html#4.2.3]
\[[FindBugs 08|AA. Java References#FindBugs 08]\] FE: Doomed test for equality to NaN

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