lib: Allow hash_get to sidestep expensive hash key generation in some cases

There is no need to generate a hash key *if* the hash_alloc_function
is NULL and the hash is empty.

This changed showed a measurable increase in performance for
table hash lookup for tables that were meant to be empty in
bgp( the distance commands ).

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/hash.c b/lib/hash.c
index d2846d7379..f222279216 100644
--- a/lib/hash.c
+++ b/lib/hash.c
@@ -143,6 +143,9 @@ void *hash_get(struct hash *hash, void *data, void *(*alloc_func)(void *))
 	void *newdata;
 	struct hash_backet *backet;
 
+	if (!alloc_func && !hash->count)
+		return NULL;
+
 	key = (*hash->hash_key)(data);
 	index = key & (hash->size - 1);