xdiff: split xrecord_t.ha into line_hash and minimal_perfect_hash

The ha field is serving two different purposes, which makes the code
harder to read. At first glance it looks like many places assume
there could never be hash collisions between lines of the two input
files. In reality, line_hash is used together with xdl_recmatch() to
ensure correct comparisons of lines, even when collisions occur.

To make this clearer, the old ha field has been split:
  * line_hash: The straightforward hash of a line, requiring no
    additional context.
  * minimal_perfect_hash: Not a new concept, but now a separate
    field. It comes from the classifier's general-purpose hash table,
    which assigns each line a unique and minimal hash across the two
    files.

Signed-off-by: Ezekiel Newren <ezekielnewren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

0 files changed, 0 insertions, 0 deletions