An apparatus and method for reconstructing a file from a difference signature and an original file

摘要

Invention maintains duplicate files in safe places. A TOKEN Table (18) reflects the indices of successive segments of the file and the exclusive-or (XR) and Cyclic Redundancy Check (CRC) products of the characters in each segment. The XR and CRC products of segments in the updated file (10) are compared to the XR and CRC products in the TOKEN Table (18). On mismatch, the segment (window) for the updated file is bumped one character and new XR and CRC products are generated and compared. The indices of the TOKEN Table (18) and the offsets are set forth in a MATCH Table (24). Next the updated file is scrolled trough to form the TRANSITION Table (36) which is the MATCH Table (24) and the updated file non-matching information. The TRANSITION Table (36) may be sent to another location (30) having a copy of the earlier file thereat. A reconstruction program at the location looks at the TRANSITION Table (36) to determine where to get the characters for the updated file it is creating.