pack-revindex: factor out `midx_key_to_pack_pos()` helper

The `midx_to_pack_pos()` function implements a binary search over
objects in the MIDX between lexical and pseudo-pack order. It does this
by taking in an index into the lexical order (i.e. the same argument
you'd use for `nth_midxed_object_id()` and similar) and spits out a
position in the pseudo-pack order.

This works for all callers, since they currently all are translating
from lexical order to pseudo-pack order. But future callers may want to
translate a known (offset, pack_id) tuple into an index into the
psuedo-pack order, without knowing where that (offset, pack_id) tuple
appears in lexical order.

Prepare for implementing a function that translates between a (offset,
pack_id) tuple into an index into the psuedo-pack order by extracting a
helper function which does just that, and then reimplementing
midx_to_pack_pos() in terms of it.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/pack-revindex.c b/pack-revindex.c
index 7dc6c776d5845ad203977d67347720156674dee7..baa4657ed3a87312233f22677059621bd1ba7ac8 100644 (file)
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -520,19 +520,12 @@ static int midx_pack_order_cmp(const void *va, const void *vb)
        return 0;
 }
 
-int midx_to_pack_pos(struct multi_pack_index *m, uint32_t at, uint32_t *pos)
+static int midx_key_to_pack_pos(struct multi_pack_index *m,
+                               struct midx_pack_key *key,
+                               uint32_t *pos)
 {
-       struct midx_pack_key key;
        uint32_t *found;
 
-       if (!m->revindex_data)
-               BUG("midx_to_pack_pos: reverse index not yet loaded");
-       if (m->num_objects <= at)
-               BUG("midx_to_pack_pos: out-of-bounds object at %"PRIu32, at);
-
-       key.pack = nth_midxed_pack_int_id(m, at);
-       key.offset = nth_midxed_offset(m, at);
-       key.midx = m;
        /*
         * The preferred pack sorts first, so determine its identifier by
         * looking at the first object in pseudo-pack order.
@@ -542,16 +535,32 @@ int midx_to_pack_pos(struct multi_pack_index *m, uint32_t at, uint32_t *pos)
         * implicitly is preferred (and includes all its objects, since ties are
         * broken first by pack identifier).
         */
-       if (midx_preferred_pack(key.midx, &key.preferred_pack) < 0)
+       if (midx_preferred_pack(key->midx, &key->preferred_pack) < 0)
                return error(_("could not determine preferred pack"));
 
-
-       found = bsearch(&key, m->revindex_data, m->num_objects,
-                       sizeof(*m->revindex_data), midx_pack_order_cmp);
+       found = bsearch(key, m->revindex_data, m->num_objects,
+                       sizeof(*m->revindex_data),
+                       midx_pack_order_cmp);
 
        if (!found)
-               return error("bad offset for revindex");
+               return -1;
 
        *pos = found - m->revindex_data;
        return 0;
 }
+
+int midx_to_pack_pos(struct multi_pack_index *m, uint32_t at, uint32_t *pos)
+{
+       struct midx_pack_key key;
+
+       if (!m->revindex_data)
+               BUG("midx_to_pack_pos: reverse index not yet loaded");
+       if (m->num_objects <= at)
+               BUG("midx_to_pack_pos: out-of-bounds object at %"PRIu32, at);
+
+       key.pack = nth_midxed_pack_int_id(m, at);
+       key.offset = nth_midxed_offset(m, at);
+       key.midx = m;
+
+       return midx_key_to_pack_pos(m, &key, pos);
+}