There is a `fastabs(z::Complex)`

defined in both SpecialFunctions.jl and Base.Math.

From its name, I would guess it computes the same thing as `abs(z::Complex)`

but faster. However

```
julia> z = 3 + 4im
3 + 4im
julia> abs(z)
5.0
julia> Base.Math.fastabs(z)
7
```

Looking at the code, the definition is

```
"""
fastabs(x::Number)
Faster `abs`-like function for rough magnitude comparisons.
`fastabs` is equivalent to `abs(x)` for most `x`,
but for complex `x` it computes `abs(real(x))+abs(imag(x))` rather
than requiring `hypot`.
"""
fastabs(x::Number) = abs(x)
fastabs(z::Complex) = abs(real(z)) + abs(imag(z))
```

What is this function used for?

I thought this was a bug and opened an issue and was told that there is some “intended behaviour”… what is the used case? It’s confusing when it says

Faster abs-like function for rough magnitude comparisons.

while 5 and 7 seems to be a pretty big difference…