[Sheepdog] [PATCH 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>
---
 include/sheep.h |   57 +++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 43 insertions(+), 14 deletions(-)

diff --git a/include/sheep.h b/include/sheep.h
index 4fd05f7..e280862 100644
--- a/include/sheep.h
+++ b/include/sheep.h
@@ -228,15 +228,29 @@ next:
 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 start, end, pos;
+
+	start = 0;
+	end = nr_entries - 1;
 
-	for (i = 0; i < nr_entries - 1; i++, e++) {
-		n = e + 1;
-		if (id > e->id && id <= n->id)
-			break;
+	if (id > entries[end].id) {
+		pos = end;
+		goto found;
 	}
-	return get_nth_node(entries, nr_entries, (i + 1) % nr_entries, idx);
+
+again:
+	pos = (end - start) / 2 + start;
+
+	if (entries[pos].id < id) {
+		if (entries[pos + 1].id >= id)
+			goto found;
+		start = pos;
+	} else
+		end = pos;
+	goto again;
+
+found:
+	return get_nth_node(entries, nr_entries, (pos + 1) % nr_entries, idx);
 }
 
 static inline int obj_to_sheep(struct sd_vnode *entries,
@@ -250,17 +264,32 @@ 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 start, end, pos, idx;
 
-	for (i = 0; i < nr_entries - 1; i++, e++) {
-		n = e + 1;
-		if (id > e->id && id <= n->id)
-			break;
+	start = 0;
+	end = nr_entries - 1;
+
+	if (id > entries[end].id) {
+		pos = end;
+		goto found;
 	}
+
+again:
+	pos = (end - start) / 2 + start;
+
+	if (entries[pos].id < id) {
+		if (entries[pos + 1].id >= id)
+			goto found;
+		start = pos;
+	} else
+		end = pos;
+	dprintf("BINARY start %d, pos %d, end %d\n", start, pos, end);
+	goto again;
+
+found:
 	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