pristine-tar can regenerate a pristine upstream tarball using only a small
binary delta file and a revision control checkout of the upstream branch.

The package also includes a pristine-gz command, which can regenerate a
pristine .gz file, a pristine-bz2 for .bz2 files, and a pristine-xz for .xz
files.

The delta file is designed to be checked into revision control along-side
the upstream branch, thus allowing Debian packages to be built entirely
using sources in revision control, without the need to keep copies of
upstream tarballs.