I finished developing software to process and read GPS L1 NAV data. The software is unique in that it performs the majority of the operations using bit operators. Identifying the L1 NAV data preamble is thereby reduced from 8 multiplications and adds to an AND and an XOR.
The software does perform parity checking on the results and seems to work correctly. Initially, the parity check was incorrectly failing on a few of the words, but the problem involved an issue with the bit referred to as D30* in the GPS specification.