How to make a function 120 times faster

General Usage
, ,
9

I guess mutable globals don’t play well with BenchmarkTools. This is how I would do the benchmarking.

using BenchmarkTools, Dictionaries
const CI = CartesianIndex.([(0,1), (1,0), (0,-1), (-1,0)])
function arcipelago(a, cidx, dcidx)
    i=1
    c=findfirst(==(-1),dcidx)
    while !isnothing(c)
        cc=CartesianIndex{2}[]
        ci=[c]
        while !isempty(ci)
            for j in ci
                a[j]=i
                dcidx[j]=1
                for n in CI
                    x=j+n
                    if haskey(dcidx,x) &&  dcidx[x]==-1      
                        dcidx[x]=0
                        push!(cc,x)
                    end
                end
            end
            ci=cc
            cc=CartesianIndex{2}[]
        end
        c=findfirst(==(-1),dcidx)
        i+=1
    end
    a
end
A = rand([1, 0], 8, 10)
@btime arcipelago(a, cidx, dcidx) setup=(a=copy(A); cidx=findall(>(0),a); dcidx=Dictionary(cidx,fill(-1, length(cidx)))) evals=1

And to reiterate, all the timing artifacts are due to repeated calls where dcidx no longer is set to -1, findfirst(==(-1), dcidx) returns nothing and the while loop isn’t ever entered. You can add some debug prints to see it in action while running @btime.

1 Like