oidset: use khash

Reimplement oidset using khash.h in order to reduce its memory footprint
and make it faster.

Performance of a command that mainly checks for duplicate objects using
an oidset, with master and Clang 6.0.1:

  $ cmd="./git-cat-file --batch-all-objects --unordered --buffer --batch-check='%(objectname)'"

  $ /usr/bin/time $cmd >/dev/null
  0.22user 0.03system 0:00.25elapsed 99%CPU (0avgtext+0avgdata 48484maxresident)k
  0inputs+0outputs (0major+11204minor)pagefaults 0swaps

  $ hyperfine "$cmd"
  Benchmark #1: ./git-cat-file --batch-all-objects --unordered --buffer --batch-check='%(objectname)'

    Time (mean ± σ):     250.0 ms ±   6.0 ms    [User: 225.9 ms, System: 23.6 ms]

    Range (min … max):   242.0 ms … 261.1 ms

And with this patch:

  $ /usr/bin/time $cmd >/dev/null
  0.14user 0.00system 0:00.15elapsed 100%CPU (0avgtext+0avgdata 41396maxresident)k
  0inputs+0outputs (0major+8318minor)pagefaults 0swaps

  $ hyperfine "$cmd"
  Benchmark #1: ./git-cat-file --batch-all-objects --unordered --buffer --batch-check='%(objectname)'

    Time (mean ± σ):     151.9 ms ±   4.9 ms    [User: 130.5 ms, System: 21.2 ms]

    Range (min … max):   148.2 ms … 170.4 ms

Initial-patch-by: Jeff King <peff@peff.net>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 22 deletions

diff --git a/oidset.c b/oidset.c
index 454c54f933..9836d427ef 100644
--- a/oidset.c
+++ b/oidset.c
@@ -3,38 +3,28 @@
 
 int oidset_contains(const struct oidset *set, const struct object_id *oid)
 {
-	if (!set->map.map.tablesize)
-		return 0;
-	return !!oidmap_get(&set->map, oid);
+	khiter_t pos = kh_get_oid(&set->set, *oid);
+	return pos != kh_end(&set->set);
 }
 
 int oidset_insert(struct oidset *set, const struct object_id *oid)
 {
-	struct oidmap_entry *entry;
-
-	if (!set->map.map.tablesize)
-		oidmap_init(&set->map, 0);
-	else if (oidset_contains(set, oid))
-		return 1;
-
-	entry = xmalloc(sizeof(*entry));
-	oidcpy(&entry->oid, oid);
-
-	oidmap_put(&set->map, entry);
-	return 0;
+	int added;
+	kh_put_oid(&set->set, *oid, &added);
+	return !added;
 }
 
 int oidset_remove(struct oidset *set, const struct object_id *oid)
 {
-	struct oidmap_entry *entry;
-
-	entry = oidmap_remove(&set->map, oid);
-	free(entry);
-
-	return (entry != NULL);
+	khiter_t pos = kh_get_oid(&set->set, *oid);
+	if (pos == kh_end(&set->set))
+		return 0;
+	kh_del_oid(&set->set, pos);
+	return 1;
 }
 
 void oidset_clear(struct oidset *set)
 {
-	oidmap_free(&set->map, 1);
+	kh_release_oid(&set->set);
+	oidset_init(set, 0);
 }