Sha1 lookup and GIT_USE_LOOKUP

Hi,
I noticed in find_pack_entry_one the use of the environment variable
GIT_USE_LOOKUP, which does not seem to be used anywhere else in git or
even in the tests.

Obviously, it determines whether or not a simple binary search or the
sha1_entry_pos method (which is apparently some kind of improved
binary search) should be used to retrieve the offset of an object
(given its sha1) in a pack.
Since this environment variable is not set by default, git will always
use a simple binary search, won't it ?

Also, when searching for a sha1 given a sha1 prefix, among packed
objects, find_short_packed_object also does a simple binary search.
Wouldn't it be simpler to just use the sha1_entry_pos method ?

Thanks

--
Marc Pegon