ZeroSpline... add option for constant abscissa step?

[BerntLie]

For the case that the step size in the abscissa is constant, the following zero_hold interpolant is some 150 times faster than ZeroSpline -- on a test case. However, I'm no super coder, so my code uses some 7 times more memory on my test case.

function zero_hold(x,dx,y)
    if x < 0
        return y[1]
    elseif x >= length(y)*dx
        return y[end]
    else
        return y[trunc(Int,x/dx)+1]
    end
end

The added speed is important (my test case is not that important -- I used a simple sinus function). But because of added memory use, in practice my code is slower when used in an ODE solver (due to garbage collection).

Would it be possible to extend the ZeroSpline interpolant to allow for constant abscissa step? With your coding expertise -- can you make it memory efficient, too? That would be super!

[ChrisRackauckas]

It would just need to specialize on range types so that way its find function is faster. That should be pretty straightforward to do just through dispatch, without actually changing most of the package.

[ChrisRackauckas]

This is the same thing as #43. We probably should do such a specialization when we see that t is a range object.