Why is anyValue % 1 "silly math" in Sonar when anyValue is a double?

Question

SonarQube raises the major violation Silly math should not be performed in my code. The description says

Certain math operations are just silly and should not be performed because their results are predictable.

In particular, anyValue % 1 is silly because it will always return 0.

In my case though, anyValue is a double. And this works as intended for me. Here's the actual code:

double v = Double.parseDouble(Utils.formatDouble(Double.valueOf(value.getValue()), accuracy.intValue()));
boolean negative = v < 0;
v = Math.abs(v);
long deg = (long) Math.floor(v);

v = (v % 1) * 60;

Is the analyser assuming my variable is an int (which is their bug)? Or am I missing something else?

Answer 1

This is indeed a bug, so thanks a lot for reporting it.

The problem is here in the code : https://github.com/SonarSource/sonar-java/blob/3.9/java-checks/src/main/java/org/sonar/java/checks/ConstantMathCheck.java#L117

where there is absolutely no check on the type of the left operand of the % operator.

I just filed the following bug to handle this : https://jira.sonarsource.com/browse/SONARJAVA-1457

Answer 2

You could make your expression more explicit by changing it to use explicit double constant like:

(v % 1.0d) * 60