Re:JavaScript Coercions Grid
by dnautics on Sunday March 31, 2019 @03:01AM
(#19534292)
-0 is truly a mistake on the part of the IEEE committee. You can get it by dividing by -infinity, it's supposed to indicate "zero approached from the left in this case, but it's not consistent; sqrt(-0) will give you -0 in most implementations
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1/–∞ == –0 seems like obviously the correct behavior in context of IEEE floats.
I think if someone is careful it should be possible to make an implementation of complex square root on top of IEEE floats such that √(–a² + 0i) == ai, whereas √(–a² – 0i) == –ai, representing the two sides of a branch cut.
Yes, √–0 should be 0. File a bug against whatever implementation returned –0 for that one.
IEEE 754 says √–0 is –0 though.
Ah really? What is the purpose of that?
Not sure.
Via https://stackoverflow.com/questions/19236117/what-numerical-... I found https://people.freebsd.org/~das/kahan86branch.pdf, but that's a more complex read than I'm prepared for right now ;)
That paper is about implementing branch cuts in a complex-valued function (e.g. complex square root), and doesn’t discuss real square roots.
In the context of that paper it seems to me that √(–0 – 0i) should be 0 – 0i and √(–0 + 0i) should be 0 + 0i, but under no circumstances should the result be –0 ± 0i, which is on the wrong branch.
The obvious extension to real-valued square root would be √(–0) == +0.