pack-objects: simplify "thin" pack.

There was a misguided logic to overly prefer using objects that
we are not going to pack as the base object.  This was
unnecessary.  It does not matter to the unpacking side where the
base object is -- it matters more to make the resulting delta
smaller.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/pack-objects.c b/pack-objects.c
index 136a7f5aad61e8a90866ee7d0b4bc22e387f0396..49357c67357fdc96e0d98b193b88e2137453c7c8 100644 (file)
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -32,9 +32,6 @@ struct object_entry {
                                 * be used as the base objectto delta huge
                                 * objects against.
                                 */
-       int based_on_preferred; /* current delta candidate is a preferred
-                                * one, or delta against a preferred one.
-                                */
 };
 
 /*
@@ -824,8 +821,6 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
 {
        struct object_entry *cur_entry = cur->entry;
        struct object_entry *old_entry = old->entry;
-       int old_preferred = (old_entry->preferred_base ||
-                            old_entry->based_on_preferred);
        unsigned long size, oldsize, delta_size, sizediff;
        long max_size;
        void *delta_buf;
@@ -867,27 +862,8 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
         * delete).
         */
        max_size = size / 2 - 20;
-       if (cur_entry->delta) {
-               if (cur_entry->based_on_preferred) {
-                       if (old_preferred)
-                               max_size = cur_entry->delta_size-1;
-                       else
-                               /* trying with non-preferred one when we
-                                * already have a delta based on preferred
-                                * one is pointless.
-                                */
-                               return -1;
-               }
-               else if (!old_preferred)
-                       max_size = cur_entry->delta_size-1;
-               else
-                       /* otherwise...  even if delta with a
-                        * preferred one produces a bigger result than
-                        * what we currently have, which is based on a
-                        * non-preferred one, it is OK.
-                        */
-                       ;
-       }
+       if (cur_entry->delta)
+               max_size = cur_entry->delta_size-1;
        if (sizediff >= max_size)
                return -1;
        delta_buf = diff_delta(old->data, oldsize,
@@ -897,7 +873,6 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
        cur_entry->delta = old_entry;
        cur_entry->delta_size = delta_size;
        cur_entry->depth = old_entry->depth + 1;
-       cur_entry->based_on_preferred = old_preferred;
        free(delta_buf);
        return 0;
 }
@@ -966,6 +941,15 @@ static void find_deltas(struct object_entry **list, int window, int depth)
                        if (try_delta(n, m, depth) < 0)
                                break;
                }
+#if 0
+               /* if we made n a delta, and if n is already at max
+                * depth, leaving it in the window is pointless.  we
+                * should evict it first.
+                * ... in theory only; somehow this makes things worse.
+                */
+               if (entry->delta && depth <= entry->depth)
+                       continue;
+#endif
                idx++;
                if (idx >= window)
                        idx = 0;