Voronoi (worley) noise in Gelato

Hello,

I am reading Advanced Renderman, and I cannot reproduce the Voronoi
noise thresholding described in the end of chapter 10 using Gelato.
Here is the code I am using:

#include "stdshader.h"
#include "noises.h"

surface test
(
    string shadingspace = "shader"
        [[  string description = "Shading space",
            string UItype = "coordsys" ]],
    float shadingfreq = 1
        [[  string description = "Shading frequency" ]]
)
{
    point Pshad = shadingfreq * transform(shadingspace, P);

    float f1, f2;
    point p1, p2;
    voronoi(Pshad, 1, f1, p1, f2, p2);
    float scalefactor = distance(p1, p2) / (distance(Pshad, p1) +
distance(Pshad, p2));
    C = step(0.05 * scalefactor, f2 - f1);
}

Can someone tell me what I am doing wrong?

SIDE NOTE:
The file implementing voronoi noise noises.h is situated in C:\Program
Files\NVIDIA Cor****ation\Gelato\shaders. From the comments I understand
that it is adapted from Renderman Shading Language implementation.
There is bug on line 171:

// The stuff that Ken Musgrave calls "VLNoise"
#define VLNoise(Pt,scale) (snoise(vsnoise(Pt)*scale+Pt))

since there is no vsnoise in Gelato, snoise should be used.