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Diffstat (limited to 'devel/xdelta/DESCR')
| -rw-r--r-- | devel/xdelta/DESCR | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/devel/xdelta/DESCR b/devel/xdelta/DESCR new file mode 100644 index 00000000000..1870b029cc2 --- /dev/null +++ b/devel/xdelta/DESCR @@ -0,0 +1,18 @@ +The delta generator portion of this program is a delta algorithm which +searches for substring matches between the files and then outputs +instructions to reconstruct the new file from the old file. It produces a +set of copy/insert instructions that tell how to reconstruct the file as a +sequence of copies from the FROM file and inserts from the delta itself. +In this regard, the program is much closer to a compression program than +to a diff program. However, the delta is not "compressed", in that the +delta's entropy H(P) will be very similar to the entropy of the portions +of the TO file not found within the FROM file. The delta will compress +just as well as the TO file will. This is a fundamentally different +method of computing deltas than in the traditional "diff" program. The +diff program and it's variants use a least-common-subsequence (LCS) +algorithm to find a list of inserts and deletes that will modify the FROM +file into the TO file. LCS is more expensive to compute and is sometimes +more useful, especially to the human reader. Since LCS is a fairly +expensive algorithm, diff programs usually divide the input files into +newline-separated "atoms" before computing a delta. This is a fine +approximation for text files, but not binary files. |