Override "S1244 - Floating point numbers should not be tested for equality" when comparing with 0 ?

[fsat...@gmail.com]

Hi,

Sometimes I need to divide two floating point numbers. To avoid a DivideByZeroException, one needs to check that the denominator is zero. However, that triggers the rule S1244.

I don't want to disable that rule because certainly comparing against a single value is usually wrong, and I want to be reminded of that. However, 0 is special in two regards:

1. It is an additive identity (x + 0 = x)

2. It is special for multiplication (x*0 =0)

3. It cannot be used for division as denominator (x/0 = undefined).

Note that values near zero do not have those properties. Therefore, I think that comparing with zero is not (almost) always an error and should not be flagged as such for this checker. 

The questions are then two: 

- would it make sense to change this rule to not warn when comparing against zero?

- is it possible to disable this rule only for this case?

Saludos

[Amaury Leve]

Hi Felipe,

It is not possible to disable the rule for only some catch (you can only mark them as FP on your SonarQube server).

About the possiblity to update the rule in order to detect this pattern, I am not sure what to say for now and will have to discuss it with the rest of the team. 

In the following code notDiviseByZero will be equal to infinity because res is not equal to 0 which is not the expected answer from a Math point of view (substracting the same value should have given 0).

var res = 0.000000000000001 - 0.000000000000001;
var notDivideByZero = 4 / res;

I am not against trying to find some pattern we could detect to avoid raising if you compare to 0 but I can't really find an easy one right now.

Cheers,

DotNet Team

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Amaury LEVÉ | SonarSource

Software Developer - .Net Team

http://sonarsource.com

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[Amaury Leve]

Hi Felipe,

We did a bit more tests and the only case where it throws an exception is when you divide by an integer 0, not a float/double 0. Also, even casting a 0 int into a float and dividing by it doesn't throw. Knowing all of this we are even more confident saying the rule is right.

In case you think we are missing something, feel free to comment here.

Cheers,

DotNet Team

[Felipe Sateler]

Hi,

Thanks for your response. I understand your reasoning, so I guess it's
ok. I'll have to make something up to not have to disable the rule.

Saludos

On Fri, Apr 21, 2017 at 10:10 AM, Amaury Leve

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Saludos,
Felipe Sateler