Hacker News Reader

Comment by scrupulusalbion | Hacker News Reader

Can arithmetic be applyied to NaN a la i? (e.g. 5 + 2 * NaN = 5 + 2NaN)

NaN is sort of viral. Any math operator (afaik) returns NaN if any of the operands is NaN. That means `5 + (2 * NaN)` becomes `5 + NaN`, which just becomes `NaN`.

Still, `5 + 2 * NaN == 5 + 2 * NaN` would return false, because it becomes `NaN == NaN`, and NaN is not equal to NaN.

what about 0 * instead of 2 * ? On one hand by the viral property it would seem to also be unequal? On the other hand having zero NaN is something every equation already has :D it seems fair to silently remove a 0 * NaN term.

"0 * NaN" makes as much sense as "0 * Blue". It's NaN because you're trying to do something that is fundamentally not multiplication.

thanks - makes sense and is a clear explanation.

It's not fair to remove 0 * NaN.

NaN will come up when doing

  Inf - Inf

But clearly:

  0 * (Inf - Inf)

cannot be said to be zero.

NaN really is not a number.

IIRC, but I don't have the IEEE spec in front of me, any operation, binary or unary, that has an operand of NaN shall have the result of NaN.

Reply on news.ycombinator.com