laplace.jl

function laplace_idiomatic (del_x::Array{Float64, 3}, x::Array{Float64, 3})

        n1, n2, n3 = size (x)
        for i3 = 2:n3-1, i2 = 2:n2-1, i1 = 2:n1-1

                del_x[i1,i2,i3] =
                        x[i1+1,i2,i3] + x[i1-1,i2,i3] +
                        x[i1,i2+1,i3] + x[i1,i2-1,i3] +
                        x[i1,i2,i3+1] + x[i1,i2,i3-1] -
                        6.0 * x[i1,i2,i3]
        end

end

function laplace_inbounds (del_x::Array{Float64, 3}, x::Array{Float64, 3})

        n1, n2, n3 = size (x)
        @inbounds begin
               for i3 = 2:n3-1, i2 = 2:n2-1, i1 = 2:n1-1

                        del_x[i1,i2,i3] =
                                x[i1+1,i2,i3] + x[i1-1,i2,i3] +
                                x[i1,i2+1,i3] + x[i1,i2-1,i3] +
                                x[i1,i2,i3+1] + x[i1,i2,i3-1] -
                                6.0 * x[i1,i2,i3]
                end
        end

end

function laplace_inbounds_linear (del_x::Array{Float64, 3}, x::Array{Float64, 3})

        n1, n2, n3 = size(x)
        @inbounds begin
                for i3 = 2:n3-1, i2 = 2:n2-1, i1 = 2:n1-1
                        index1 = n1 * ((i3 - 1) * n2 + (i2 - 1)) + i1 
                        index2 = n1 * ((i3 - 1) * n2 + (i2 - 1)) + i1 + 1
                        index3 = n1 * ((i3 - 1) * n2 + (i2 - 1)) + i1 - 1
                        index4 = n1 * ((i3 - 1) * n2 + (i2 - 2)) + i1
                        index5 = n1 * ((i3 - 1) * n2 + (i2 - 0)) + i1
                        index6 = n1 * ((i3 - 2) * n2 + (i2 - 1)) + i1
                        index7 = n1 * ((i3 - 0) * n2 + (i2 - 1)) + i1                        
                        del_x[index1] = x[index2] + x[index3] +
                                        x[index4] + x[index5] +
                                        x[index6] + x[index7] -
                                        6.0 * x[index1]
                end
        end

end

laplace_bench.jl

require ("laplace.jl")

function main ()
        niters = 10
        n = 300
        field = init_field (n)
        del_field = zeros (size (field))

        # warmup Julia
        laplace_idiomatic (del_field, field)
        laplace_inbounds (del_field, field)
        laplace_inbounds_linear (del_field, field)

        # timing idiomatic Julia version
        tic ()
        for n = 1:niters
                laplace_idiomatic (del_field, field)
        end
        write (STDOUT, "Julia (idiomatic): ")
        toc ()

        # timing inbounds Julia version
        tic ()
        for n = 1:niters
                laplace_inbounds (del_field, field)
        end
        write (STDOUT, "Julia (inbounds): ")
        toc ()

        # timing inbounds linear Julia version
        tic ()
        for n = 1:niters
                laplace_inbounds_linear (del_field, field)
        end
        write (STDOUT, "Julia (inbounds, linear): ")
        toc ()
end

function init_field (n::Int64)

        field = zeros (n, n, n)
        for i1 = 1:n, i2 = 1:n, i3 = 1:n
                if i1 == 1 || i2 == 1 || i3 == 1 || i1 == n || i2 == n || i3 == n
                        field[i1,i2,i3] = 1.0
                end
        end
        field

end

main ()