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| 국가/구분 | United States(US) Patent 등록 |
|---|---|
| 국제특허분류(IPC7판) |
|
| 출원번호 | US-0039702 (1993-03-30) |
| 발명자 / 주소 |
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| 출원인 / 주소 |
|
| 인용정보 | 피인용 횟수 : 295 인용 특허 : 0 |
Invention maintains duplicate files in safe places. A SCAN computer program creates a TOKEN Table of an earlier file. The TOKEN Table 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. An upd
Invention maintains duplicate files in safe places. A SCAN computer program creates a TOKEN Table of an earlier file. The TOKEN Table 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. An updated file is compared to the earlier file by comparing the XR and CRC products of segments in the updated file to the XR and CRC products in the TOKEN Table. On detecting matching products for identical segments, the next segments are compared. On mismatch, the segment (window) for the updated file is bumped one character and new XR and CRC products generated and compared. The indices of the TOKEN Table and the offsets from the start of the file of the first characters of the updated file matching segments are set forth in a Match Table. Next the updated file is scrolled through for the non-matching information determined by acting on the indices and offsets of the Match Table to form the TRANSITION Table which is the Match Table and the updated file non-matching information. The TRANSITION Table contains the delta information which may be sent to another location having a copy of the earlier file thereat: the whole updated file need not be sent there. A reconstruction program at the location looks at the TRANSITION Table to determine where to get the characters for the copy of the updated file it is creating.
A method for producing a difference signature of differences between an original file and an updated version of the original file, comprising (1) creating a token table from an original file in a first storage device by producing a token set for each equal sized contiguous segment of said original f
A method for producing a difference signature of differences between an original file and an updated version of the original file, comprising (1) creating a token table from an original file in a first storage device by producing a token set for each equal sized contiguous segment of said original file, each token set comprising a primary exclusive-or based token and at least one order sensitive secondary token or cyclic redundancy check product term; and (2) generating a difference signature, using the token table and an updated file, by: (a) defining a window of consideration for the updated file, said window being of a size equivalent to the segment size used to create the token set for the original file and comprising successive characters in the updated file; (b) calculating a primary exclusive-or based token for the window of consideration; (c) searching the token table for a primary token which matches the primary token for the window and advancing to step 2(g) if said matching primary token is not found in the token table; (d) (i) generating a secondary token for said window in response to finding in the token table a primary token which matches the primary token from the window and comparing the secondary token to the secondary token in the corresponding token set in the token table; and (ii) advancing to step 2(e) if the secondary tokens match; (e) logging the offset of the current window to the difference signature to correlate the relative locations of the matching segment in the original and updated files, in response to finding a match between the secondary token from the window and the corresponding secondary token from the token set; (f) advancing the window of consideration by the segment size to the next segment after the matched text, if there are any remaining segments in the updated file, and resuming the method at step (2b) above; (g) advancing the window of consideration by at least one character to create the next window, which includes the characters of the previous window and at least one character in the updated file following the previous window minus the equivalent number of characters at the beginning of the previous window, in response to a failed token search for the previous window, which occurs where either said primary token for the previous window of said updated file is not found in the token table for said original file or where at least one matching primary token is found in the token table but no matching secondary token corresponding to said at least one matching primary token is found in the token table; (h) generating a primary token for said next window of consideration by adjusting the primary token from the previous window and (j) repeating the cycle of steps (2b) through (2i) until the updated file is exhausted.
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