Clamping Houdini native SDF fields, for https://jurajtomori.wordpress.com/2018/07/09/houdini-tip-houdini-native-volume-sdf-into-vdb-conversion/

volumewrangle_clamp.c

float dist = chf("dist");
int voxels = chi("voxels");
int mode = chi("voxels_dist_mode");

float voxel_size = volumevoxeldiameter(0, 0) / sqrt(3);

float val;
if (mode)
    val = dist;
else
    val = voxel_size * voxels;

f@surface = clamp(f@surface, -val, val);