On 12 Jun 2019, at 10:28pm, James K. Lowden <jklow...@schemamania.org> wrote:
> what kind of computation
> would lead to a value in memory representing -0,0?
Here's the classic answer. It's not very impressive or convincing because it
just kicks the can further down the road.
Suppose you have a system like IEEE754 which represents positive infinity and
negative infinity as two different values. At some point you calculate a
a <-- 20.0 / c
where c is zero. The answer is positive or negative infinity depending on
whether c is positive or negative zero.
Now, you could answer that they're both infinity and the answer doesn't matter
because you can't calculate with infinity. But suppose later you do
IF a > 4 THEN …
or
z = a + [-ve infinity]
Keeping different values for the two zeros may allow you to answer these
questions correctly. Without that you cannot know the answer.
This is one of the reasons I asked whether SQLite was going to distinguish
between +inf and -inf, and have NaN values. So if SQLite already shows +inf
and -inf differently as text, it should do the same thing for the two zeros.
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