A method of generating hash codes from a query vector. An ordering of dimensions is determined for a lattice hole in an A* lattice, the lattice hole being located nearest to the query vector and the ordering of dimensions represents a mapping applied to transform a canonical hole of the A* lattice to the lattice hole. An initial hash code is determined for a first point in the A* lattice, based on the query vector, using a plurality of predetermined constants. A subsequent hash code is generated for a second point in the A* lattice, from the initial hash code by modifying the initial hash code by a multiple of a constant. The constant is selected from the plurality of predetermined constants using the determined ordering of dimensions.