On Tue, Feb 10, 2009 at 03:05:57PM -0800, Junio C Hamano wrote:
> There is an obvious optimization you can do to "diff-index --cached" using
> cache-tree. If your index is really clean, computing the tree object the
> index would represent (without writing the tree object out) and comparing
> it against HEAD^{tree} may be a tad faster.
Clever, but I think you may just be trading one scenario for "worst
case" versus another (i.e., now when you _do_ have a difference to do an
early return, you still have to touch everything in the cache).
Just for fun, I timed a quick and dirty implementation. It looks like
generating the tree actually ends up taking just a little bit longer,
even with an unchanged index (which should be the case it speeds up).
But maybe I just did it wrong. My implementation was basically just:
t = cache_tree();
if (!cache_tree_fully_valid(t))
cache_tree_update(t, active_cache, active_nr, 0, 0);
get_sha1("HEAD", sha1);
return hashcmp(t->sha1, sha1);
-Peff
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