On Thu, Jul 12, 2007 at 02:38:30AM -0400, Nicolas Pitre wrote:
> This apparently makes BRian's patological case worse (although better
> than before his same-size-shallower patch), but I think that the
> improvement in the general case is worth it. Even Brian's pack gets
> smaller so...
I've found why this makes my case worse, and I think it's correctable
and will benefit everything when fixed:
Let's say we've currently got a delta match of 11 bytes at depth 5.
So trg_entry->delta_size = 11 and trg_entry->depth = 5. max_depth is
100.
Now let's say the next object we're comparing against is at depth 2
(src_entry->depth = 2). Even if we can find a delta of the same size
we should take it.
Now, with Nico's new patch:
max_size = trg_entry->delta_size * max_depth /
(max_depth - trg_entry->depth + 1);
max_size is now 11. So far so good.
Now, however, the other bias happens:
max_size = max_size * (max_depth - src_entry->depth) / max_depth;
max_size = 11 * (100 - 2) / 100;
max_size = 1078 / 100;
max_size = 10;
This was okay when max_size was always (trg_size/2 - 20) here, but now
it's cutting it off too much. max_size is now 10, and we can't make
a better depth match of the same size anymore.
I think the second bias equation should be scaled so as not to take
effect unless (src_entry->depth [+ 1?] > trg_entry->depth).
Other than this flaw I think this patch looks great.
-bcd
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