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0 pointsncurses101013d ago0 comments

With the default initialization to nan, do you ever run into situations where people are searching for common sources for nan (nan literals, div by zero) and they can't find it? Or cases where only some branches but not others initialize the float?

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WalterBright13d ago

To leave a variable uninitialized, use the construction:

    int x = void;

Note that nobody is going to write this by accident. And it's easy to grep for.

To find the source of a NaN, it helps to know that every operation that has a NaN as an operand produces a NaN as a result. So if you see a NaN in the output, you can work backwards to where it originated.

jcranmer13d ago

> every operation that has a NaN as an operand produces a NaN as a result.

That's not true. The minimum/maximum functions (fmin and fminimum_num variants, but not the fminimum one) treat NaN inputs as not-present, so return the non-NaN value if there is one. Similarly, hypot also treats NaN inputs as not-present. pow and compoundn will ignore NaN exponents if the base is 1.

WalterBright13d ago

Yes, there are some functions where if one operand has no effect on the result, a NaN value will also have no effect.

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0 comments

WalterBright13d ago

To leave a variable uninitialized, use the construction:

    int x = void;

Note that nobody is going to write this by accident. And it's easy to grep for.

jcranmer13d ago

> every operation that has a NaN as an operand produces a NaN as a result.

WalterBright13d ago

Yes, there are some functions where if one operand has no effect on the result, a NaN value will also have no effect.

j / k navigate · click thread line to collapse