Fast Dict value modification by accessing Dict.vals

General Usage Performance
10

The original simple version I had was:

function mapdict!(f, d::Dict)
    L = length(d.vals)
    i = d.idxfloor
    vals = d.vals
    Base.@inbounds while i < L
        Base.isslotfilled(d, i) && (vals[i] = f(vals[i]))
        i += 1
    end
end

Is only about 10% faster without the functionality.