Subsequent patches will introduce file formats that make use of a fanout
array and a sorted table containing hashes, just like packfiles.
Refactor the hash search in packfile.c into its own function, so that
those patches can make use of it as well.
Signed-off-by: Jonathan Tan <jonathantanmy@xxxxxxxxxx>
---
packfile.c | 19 +++++--------------
sha1-lookup.c | 24 ++++++++++++++++++++++++
sha1-lookup.h | 21 +++++++++++++++++++++
3 files changed, 50 insertions(+), 14 deletions(-)
diff --git a/packfile.c b/packfile.c
index 58bdced3b..29f5dc239 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1712,7 +1712,8 @@ off_t find_pack_entry_one(const unsigned char *sha1,
{
const uint32_t *level1_ofs = p->index_data;
const unsigned char *index = p->index_data;
- unsigned hi, lo, stride;
+ unsigned stride;
+ int ret;
if (!index) {
if (open_pack_index(p))
@@ -1725,8 +1726,6 @@ off_t find_pack_entry_one(const unsigned char *sha1,
index += 8;
}
index += 4 * 256;
- hi = ntohl(level1_ofs[*sha1]);
- lo = ((*sha1 == 0x0) ? 0 : ntohl(level1_ofs[*sha1 - 1]));
if (p->index_version > 1) {
stride = 20;
} else {
@@ -1734,17 +1733,9 @@ off_t find_pack_entry_one(const unsigned char *sha1,
index += 4;
}
- while (lo < hi) {
- unsigned mi = lo + (hi - lo) / 2;
- int cmp = hashcmp(index + mi * stride, sha1);
-
- if (!cmp)
- return nth_packed_object_offset(p, mi);
- if (cmp > 0)
- hi = mi;
- else
- lo = mi+1;
- }
+ ret = bsearch_hash(sha1, level1_ofs, index, stride);
+ if (ret >= 0)
+ return nth_packed_object_offset(p, ret);
return 0;
}
diff --git a/sha1-lookup.c b/sha1-lookup.c
index 4cf3ebd92..d11c5e526 100644
--- a/sha1-lookup.c
+++ b/sha1-lookup.c
@@ -99,3 +99,27 @@ int sha1_pos(const unsigned char *sha1, void *table, size_t nr,
} while (lo < hi);
return -lo-1;
}
+
+int bsearch_hash(const unsigned char *sha1, const void *fanout_,
+ const void *table_, size_t stride)
+{
+ const uint32_t *fanout = fanout_;
+ const unsigned char *table = table_;
+ int hi, lo;
+
+ hi = ntohl(fanout[*sha1]);
+ lo = ((*sha1 == 0x0) ? 0 : ntohl(fanout[*sha1 - 1]));
+
+ while (lo < hi) {
+ unsigned mi = lo + (hi - lo) / 2;
+ int cmp = hashcmp(table + mi * stride, sha1);
+
+ if (!cmp)
+ return mi;
+ if (cmp > 0)
+ hi = mi;
+ else
+ lo = mi + 1;
+ }
+ return -lo - 1;
+}
diff --git a/sha1-lookup.h b/sha1-lookup.h
index cf5314f40..3c59e9cb1 100644
--- a/sha1-lookup.h
+++ b/sha1-lookup.h
@@ -7,4 +7,25 @@ extern int sha1_pos(const unsigned char *sha1,
void *table,
size_t nr,
sha1_access_fn fn);
+
+/*
+ * Searches for sha1 in table, using the given fanout table to determine the
+ * interval to search, then using binary search. Returns the element index of
+ * the position found if successful, -i-1 if not (where i is the index of the
+ * least element that is greater than sha1).
+ *
+ * Takes the following parameters:
+ *
+ * - sha1: the hash to search for
+ * - fanout: a 256-element array of NETWORK-order 32-bit integers; the integer
+ * at position i represents the number of elements in table whose first byte
+ * is less than or equal to i
+ * - table: a sorted list of hashes with optional extra information in between
+ * - stride: distance between two consecutive elements in table (should be
+ * GIT_MAX_RAWSZ or greater)
+ *
+ * This function does not verify the validity of the fanout table.
+ */
+extern int bsearch_hash(const unsigned char *sha1, const void *fanout,
+ const void *table, size_t stride);
#endif
--
2.16.0.rc1.238.g530d649a79-goog
