That OpenVDB data structure is a sparse hierarchical collection with a huge count of small 3D blocks of voxels. They use bit masks in the blocks to track which

That OpenVDB data structure is a sparse hierarchical collection with a huge count of small 3D blocks of voxels. They use bit masks in the blocks to track which voxels are empty, and which contain the payload data or higher resolution child blocks. That’s why these bit manipulation instructions contributed that much to the overall performance of the library. I saw similar approach in other software as well. Not necessarily for voxels, also 2D data, and trees where nodes use bits to track children.