For each seed fragment, we compute its rotational transformations about the geometric center which is fixed at the coordinate origin. Accordingly, we first compute 256 uniformly distributed unit vectors around the coordinate origin. Then, the seed fragment is rotated by 10° increments around the axis formed by each unit vector. To speed up the subsequent step of rigid fragment docking, the rotated fragment atoms' coordinates are mapped on a hexagonal close-packed (HCP) grid of 0.375 Å resolution. This mapping enables efficient docking of fragments to a protein binding site since their rotational transformations need to be computed only once. The fragment's clashes with the protein and the fragment's RMR6 scores are determined by translations of the rotational fragment grid over the compatible HCP binding site grid using fast integer arithmetic.