473     gridindex curvox, step, out;  in grid_intersect()  local
494         step.x = 0;  in grid_intersect()
500         step.x = out.x = -1;  in grid_intersect()
505         step.x = 1;  in grid_intersect()
513         step.y = 0;  in grid_intersect()
519         step.y = out.y = -1;  in grid_intersect()
524         step.y = 1;  in grid_intersect()
532         step.z = 0;  in grid_intersect()
538         step.z = out.z = -1;  in grid_intersect()
543         step.z = 1;  in grid_intersect()
569             curvox.x += step.x;  in grid_intersect()
572             voxindex += step.x;  in grid_intersect()
588             curvox.z += step.z;  in grid_intersect()
591             voxindex += step.z * g->xsize * g->ysize;  in grid_intersect()
607             curvox.y += step.y;  in grid_intersect()
610             voxindex += step.y * g->xsize;  in grid_intersect()