An apparatus, system, and method is described for calculating a composite index into a customizable hybrid address space that is at least partially compressed to locate a longest prefix match (“LPM”) of a prefix string comprised of a plurality of multi-bit strides (“MBSs”). The device comprises: a mask-and-count logic for generating a base index into memory for a first MBS whose addresses are not compressed; a logical-shift apparatus that selectively uses a variable portion of the second MBS to generate an offset index from the given base index per an amount the second MBS addresses were actually compressed; and an add logic that adds the base index to the offset index to form the composite index that locates the LPM using a single access into memory. A compressed vector contains compression information of the second MBS in an information density format greater than a single bit to a single address.