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| author | Junio C Hamano <gitster@pobox.com> | 2007-06-29 06:11:40 (GMT) |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2007-07-01 03:51:31 (GMT) |
| commit | af3abef94af9c821a0c192c693c3e5342ab8729f (patch) | |
| tree | 6bb78aa5ea7806078487e16ef55d03d3f042495c /diffcore-delta.c | |
| parent | 706098af6b53403b5ea3db9216fb99afbe06f52d (diff) | |
| download | git-af3abef94af9c821a0c192c693c3e5342ab8729f.zip git-af3abef94af9c821a0c192c693c3e5342ab8729f.tar.gz git-af3abef94af9c821a0c192c693c3e5342ab8729f.tar.bz2 | |
diffcore-delta.c: update the comment on the algorithm.
The comment at the top of the file described an old algorithm
that was neutral to text/binary differences (it hashed sliding
window of N-byte sequences and counted overlaps), but long time
ago we switched to a new heuristics that are more suitable for
line oriented (read: text) files that are much faster.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'diffcore-delta.c')
| -rw-r--r-- | diffcore-delta.c | 21 |
1 files changed, 9 insertions, 12 deletions
diff --git a/diffcore-delta.c b/diffcore-delta.c index 0e1fae7..7116df0 100644 --- a/diffcore-delta.c +++ b/diffcore-delta.c @@ -5,23 +5,20 @@ /* * Idea here is very simple. * - * We have total of (sz-N+1) N-byte overlapping sequences in buf whose - * size is sz. If the same N-byte sequence appears in both source and - * destination, we say the byte that starts that sequence is shared - * between them (i.e. copied from source to destination). + * Almost all data we are interested in are text, but sometimes we have + * to deal with binary data. So we cut them into chunks delimited by + * LF byte, or 64-byte sequence, whichever comes first, and hash them. * - * For each possible N-byte sequence, if the source buffer has more - * instances of it than the destination buffer, that means the - * difference are the number of bytes not copied from source to - * destination. If the counts are the same, everything was copied - * from source to destination. If the destination has more, - * everything was copied, and destination added more. + * For those chunks, if the source buffer has more instances of it + * than the destination buffer, that means the difference are the + * number of bytes not copied from source to destination. If the + * counts are the same, everything was copied from source to + * destination. If the destination has more, everything was copied, + * and destination added more. * * We are doing an approximation so we do not really have to waste * memory by actually storing the sequence. We just hash them into * somewhere around 2^16 hashbuckets and count the occurrences. - * - * The length of the sequence is arbitrarily set to 8 for now. */ /* Wild guess at the initial hash size */ |