[Sheepdog] [PATCH v2 2/2] use binary search in hval_to_sheep()

[levin li]

As we know, binary search is much faster than sequential search,
we can use binary search to make hval_to_sheep() faster.

Signed-off-by: levin li <xingke.lwp at taobao.com>
---

Patch update:

add a bsearch helper bsearch_in_entries()

 include/sheep.h |   44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/include/sheep.h b/include/sheep.h
index 4fd05f7..9537970 100644
--- a/include/sheep.h
+++ b/include/sheep.h
@@ -225,18 +225,35 @@ next:
 	return idx;
 }
 
+static inline int bsearch_in_entries(struct sd_vnode *entries,
+			int nr_entries, uint64_t id)
+{
+	int start, end, pos;
+
+	start = 0;
+	end = nr_entries - 1;
+
+	if (id > entries[end].id)
+		return end;
+again:
+	pos = (end - start) / 2 + start;
+	if (entries[pos].id < id) {
+		if (entries[pos + 1].id >= id)
+			return pos;
+		start = pos;
+	} else
+		end = pos;
+	goto again;
+
+	return pos;
+}
+
 static inline int hval_to_sheep(struct sd_vnode *entries,
 				int nr_entries, uint64_t id, int idx)
 {
-	int i;
-	struct sd_vnode *e = entries, *n;
+	int pos = bsearch_in_entries(entries, nr_entries, id);
 
-	for (i = 0; i < nr_entries - 1; i++, e++) {
-		n = e + 1;
-		if (id > e->id && id <= n->id)
-			break;
-	}
-	return get_nth_node(entries, nr_entries, (i + 1) % nr_entries, idx);
+	return get_nth_node(entries, nr_entries, (pos + 1) % nr_entries, idx);
 }
 
 static inline int obj_to_sheep(struct sd_vnode *entries,
@@ -250,17 +267,12 @@ static inline int obj_to_sheep(struct sd_vnode *entries,
 static inline void hval_to_sheeps(struct sd_vnode *entries,
 			int nr_entries, uint64_t id, int nr_copies, int *idxs)
 {
-	int i, idx;
-	struct sd_vnode *e = entries, *n;
+	int idx;
+	int pos = bsearch_in_entries(entries, nr_entries, id);
 
-	for (i = 0; i < nr_entries - 1; i++, e++) {
-		n = e + 1;
-		if (id > e->id && id <= n->id)
-			break;
-	}
 	for (idx = 0; idx < nr_copies; idx++)
 		idxs[idx] = get_nth_node(entries, nr_entries,
-				(i + 1) % nr_entries, idx);
+				(pos + 1) % nr_entries, idx);
 }
 
 static inline void obj_to_sheeps(struct sd_vnode *entries,
-- 
1.7.10