packfile: define and use bsearch_pack()

The method bsearch_hash() generalizes binary searches using a
fanout table. The only consumer is currently find_pack_entry_one().
It requires a bit of pointer arithmetic to align the fanout table
and the lookup table depending on the pack-index version.

Extract the pack-index pointer arithmetic to a new method,
bsearch_pack(), so this can be re-used in other code paths.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/packfile.c b/packfile.c
index f26395ecabb39470f0ddfd127a417439a09de432..69d3afda6c5b3fd15cab7a32eb50028bba0b6c67 100644 (file)
--- a/packfile.c
+++ b/packfile.c
@@ -1654,6 +1654,29 @@ out:
        return data;
 }
 
+int bsearch_pack(const struct object_id *oid, const struct packed_git *p, uint32_t *result)
+{
+       const unsigned char *index_fanout = p->index_data;
+       const unsigned char *index_lookup;
+       int index_lookup_width;
+
+       if (!index_fanout)
+               BUG("bsearch_pack called without a valid pack-index");
+
+       index_lookup = index_fanout + 4 * 256;
+       if (p->index_version == 1) {
+               index_lookup_width = 24;
+               index_lookup += 4;
+       } else {
+               index_lookup_width = 20;
+               index_fanout += 8;
+               index_lookup += 8;
+       }
+
+       return bsearch_hash(oid->hash, (const uint32_t*)index_fanout,
+                           index_lookup, index_lookup_width, result);
+}
+
 const unsigned char *nth_packed_object_sha1(struct packed_git *p,
                                            uint32_t n)
 {
@@ -1720,30 +1743,17 @@ off_t nth_packed_object_offset(const struct packed_git *p, uint32_t n)
 off_t find_pack_entry_one(const unsigned char *sha1,
                                  struct packed_git *p)
 {
-       const uint32_t *level1_ofs = p->index_data;
        const unsigned char *index = p->index_data;
-       unsigned stride;
+       struct object_id oid;
        uint32_t result;
 
        if (!index) {
                if (open_pack_index(p))
                        return 0;
-               level1_ofs = p->index_data;
-               index = p->index_data;
-       }
-       if (p->index_version > 1) {
-               level1_ofs += 2;
-               index += 8;
-       }
-       index += 4 * 256;
-       if (p->index_version > 1) {
-               stride = 20;
-       } else {
-               stride = 24;
-               index += 4;
        }
 
-       if (bsearch_hash(sha1, level1_ofs, index, stride, &result))
+       hashcpy(oid.hash, sha1);
+       if (bsearch_pack(&oid, p, &result))
                return nth_packed_object_offset(p, result);
        return 0;
 }

diff --git a/packfile.h b/packfile.h
index a7fca598d672b73010a5fb99e4507da4634002ff..ec08cb2bb039ef005b90e09bcf35e90c5cbfb54b 100644 (file)
--- a/packfile.h
+++ b/packfile.h
@@ -78,6 +78,14 @@ extern struct packed_git *add_packed_git(const char *path, size_t path_len, int
  */
 extern void check_pack_index_ptr(const struct packed_git *p, const void *ptr);
 
+/*
+ * Perform binary search on a pack-index for a given oid. Packfile is expected to
+ * have a valid pack-index.
+ *
+ * See 'bsearch_hash' for more information.
+ */
+int bsearch_pack(const struct object_id *oid, const struct packed_git *p, uint32_t *result);
+
 /*
  * Return the SHA-1 of the nth object within the specified packfile.
  * Open the index if it is not already open.  The return value points