>>>>> "Jeff" == Jeff King <peff@xxxxxxxx> writes:
Jeff> On Thu, Oct 26, 2006 at 05:57:20PM +0800, James Henstridge wrote:
>> >If you two have the same commit that is a guarantee that you two
>> >have identical trees. The reverse is not true as logic 101
>> >would teach ;-).
>>
>> That was the point I was trying to make. Carl asserted that in git
>> you could tell if you had the same tree as someone else based on
>> revision IDs, which doesn't seem to be the case all the time.
Jeff> If you have the same revision (commit IDs), you have
Jeff> the same tree (at the same time, by the same committer,
Jeff> etc).
Jeff> If you have a different revision (commit), you may or
Jeff> may not have the same tree. You can then check the tree
Jeff> id, which will either be the same (you have the same
Jeff> tree) or differ (you don't).
Jeff> Thus, in the converse, if you have the same tree, you
Jeff> _will_ have the same tree id. You may or may not have
Jeff> the same commit id.
Ok, so git make a distinction between the commit (code created by
someone) and the tree (code only).
Commits are defined by their parents.
Trees are defined by their content only ?
If that's the case, how do you proceed ?
Calculate a sha1 representing the content (or the content of the
diff from parent) of all the files and dirs in the tree ? Or
from the sha1s of the files and dirs themselves recursively based
on sha1s of the files and dirs they contain ?
I ask because the later seems to provide some nice effects
similar to what makes BDD
(http://en.wikipedia.org/wiki/Binary_decision_diagram) so
efficient: you can compare graphs of any complexity or size in
O(1) by just comparing their signatures.
Vincent
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