pack-objects: Prefer shallower deltas if the size is equal

Change "try_delta" so that if it finds a delta that has the same size
but shallower depth than the existing delta, it will prefer the
shallower one.  This makes certain delta trees vastly less deep.

Signed-off-by: Brian Downing <bdowning@lavos.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 3d396ca37ac1356c7974aaaf34af39bcd0cf6bae..54b9d268da7d3b968f7a950dbe8bad9c2735e345 100644 (file)
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -1337,7 +1337,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
        if (max_size == 0)
                return 0;
        if (trg_entry->delta && trg_entry->delta_size <= max_size)
-               max_size = trg_entry->delta_size-1;
+               max_size = trg_entry->delta_size;
        src_size = src_entry->size;
        sizediff = src_size < trg_size ? trg_size - src_size : 0;
        if (sizediff >= max_size)
@@ -1371,6 +1371,12 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
                return 0;
 
        if (trg_entry->delta_data) {
+               /* Prefer only shallower same-sized deltas. */
+               if (delta_size == trg_entry->delta_size &&
+                   src_entry->depth + 1 >= trg_entry->depth) {
+                       free(delta_buf);
+                       return 0;
+               }
                delta_cache_size -= trg_entry->delta_size;
                free(trg_entry->delta_data);
        }