`hypot` with both arguments 0 returns NaN with Unitful.jl

[SebastianM-C]

#34316 introduced

hypot(x::T, y::T) where {T<:Number} = (z = y/x; abs(x) * sqrt(one(z) + z*z))

If iszero(x) and iszero(y), the above returns NaN instead of zero(T).

To trigger this one can use:

using Unitful
hypot(0u"m",0u"m")

One way to fix this would be

hypot(x::T, y::T) where {T<:Number} = !iszero(x) ? (z = y/x; abs(x) * sqrt(one(z) + z*z)) : abs(y)

If the above is ok, I can make a PR.

julia> versioninfo()
Julia Version 1.4.0-rc1.0
Commit b0c33b0cf5 (2020-01-23 17:23 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-7800X CPU @ 3.50GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-8.0.1 (ORCJIT, skylake)
Environment:
  JULIA_NUM_THREADS = 6

[giordano]

I think it was #33224 that removed too much code. CC @musm

[StefanKarpinski]

That attempt at avoiding overflow generically strikes me as a bit too clever, but 🤷‍♂

[JeffBezanson]

Yes might as well PR that change.

[JeffBezanson]

Fixed by #34817