A 4D voronoi OSL shader for Blender Cycles

I took a post on Blender Artists as a challenge and created a 4D voronoi shader.

Blogspot won't show animated gifs but I put up a short sequence on PasteAll and if that doesn't work it is also on my site. In this animated gif, the fourth dimension (time) is animated from 0 to 1 in 50 frames.
The shader presented below is simple enough but convoluted because we cannot manipulate arrays like points or vectors in OSL but otherwise it is a straight forward extension of Blenders bundled voronoi implementation, especially because OSLs cellnoise function supports 4D noise out of the box (you can pass it a point and a float).
#include "stdosl.h"

void cellnoise_color4d(float p[4], float c[4])
{
 c[0] = cellnoise(point(p[0],p[1],p[2]),p[3]);
 c[1] = cellnoise(point(p[1],p[0],p[2]),p[3]);
 c[2] = cellnoise(point(p[1],p[2],p[0]),p[3]);
 c[3] = cellnoise(point(p[3],p[1],p[2]),p[0]);
}

/* Voronoi 4D . we always use distance squared as the distance metric */

void voronoi4d(point p, float t, float da[4], point pa[4], float ta[4])
{
 /* returns distances in da, point coords in pa and time coords in ta*/
 int xx, yy, zz, tt, xi, yi, zi, ti;

 float op[4] = {p[0],p[1],p[2],t};
 
 xi = (int)floor(p[0]);
 yi = (int)floor(p[1]);
 zi = (int)floor(p[2]);
 ti = (int)floor(t);

 da[0] = 1e10;
 da[1] = 1e10;
 da[2] = 1e10;
 da[3] = 1e10;

 for (xx = xi - 1; xx <= xi + 1; xx++) {
  for (yy = yi - 1; yy <= yi + 1; yy++) {
   for (zz = zi - 1; zz <= zi + 1; zz++) {
    for (tt = ti - 1; tt <= ti + 1; tt++) {
     float ip[4] = {xx, yy, zz, tt};
     float vp[4];
     cellnoise_color4d(ip,vp);
     float pd[4] = { op[0] - (vp[0] + ip[0]), 
         op[1] - (vp[1] + ip[1]),
         op[2] - (vp[2] + ip[2]),
         op[3] - (vp[3] + ip[3])};
     // always distance squared
     float d = pd[0]*pd[0]+pd[1]*pd[1]+pd[2]*pd[2]+pd[3]*pd[3];

     vp[0] += xx;
     vp[1] += yy;
     vp[2] += zz;
     vp[3] += tt;

     if (d < da[0]) {
      da[3] = da[2];
      da[2] = da[1];
      da[1] = da[0];
      da[0] = d;

      pa[3] = pa[2]; ta[3] = ta[2];
      pa[2] = pa[1]; ta[2] = ta[1];
      pa[1] = pa[0]; ta[1] = ta[0];
      pa[0] = point(vp[0],vp[1],vp[2]); ta[0] = vp[3];
     }
     else if (d < da[1]) {
      da[3] = da[2];
      da[2] = da[1];
      da[1] = d;

      pa[3] = pa[2]; ta[3] = ta[2];
      pa[2] = pa[1]; ta[2] = ta[1];
      pa[1] = point(vp[0],vp[1],vp[2]); ta[1] = vp[3];
     }
     else if (d < da[2]) {
      da[3] = da[2];
      da[2] = d;

      pa[3] = pa[2]; ta[3] = ta[2];
      pa[2] = point(vp[0],vp[1],vp[2]); ta[2] = vp[3];
     }
     else if (d < da[3]) {
      da[3] = d;
      pa[3] = point(vp[0],vp[1],vp[2]); ta[3] = vp[3];
     }
    }
   }
  }
 }
}

shader node_voronoi_texture(
 float Scale = 5.0,
 point Vector = P,
 float Time = 0,
 output float Fac = 0.0,
 output color Color = color(0.0, 0.0, 0.0))
{
 point p = Vector;

 /* compute distance and point coordinate of 4 nearest neighbours */
 float da[4];
 point pa[4];
 float ta[4];
 
 voronoi4d(p * Scale, Time * Scale, da, pa, ta);

 Fac = fabs(da[0]);
 Color = color(Fac);
}

Example node setup

Straight forward enough but note the keyframed Time value.

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