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-rw-r--r--lib/hash.c65
-rw-r--r--lib/hash.h6
2 files changed, 66 insertions, 5 deletions
diff --git a/lib/hash.c b/lib/hash.c
index 1e097f28..987012a5 100644
--- a/lib/hash.c
+++ b/lib/hash.c
@@ -48,7 +48,7 @@ struct hash *
hash_create (unsigned int (*hash_key) (void *),
int (*hash_cmp) (const void *, const void *))
{
- return hash_create_size (HASHTABSIZE, hash_key, hash_cmp);
+ return hash_create_size (HASH_INITIAL_SIZE, hash_key, hash_cmp);
}
/* Utility function for hash_get(). When this function is specified
@@ -60,6 +60,52 @@ hash_alloc_intern (void *arg)
return arg;
}
+/* Expand hash if the chain length exceeds the threshold. */
+static void hash_expand (struct hash *hash)
+{
+ unsigned int i, new_size, losers;
+ struct hash_backet *hb, *hbnext, **new_index;
+
+ new_size = hash->size * 2;
+ new_index = XCALLOC(MTYPE_HASH_INDEX, sizeof(struct hash_backet *) * new_size);
+ if (new_index == NULL)
+ return;
+
+ for (i = 0; i < hash->size; i++)
+ for (hb = hash->index[i]; hb; hb = hbnext)
+ {
+ unsigned int h = hb->key & (new_size - 1);
+
+ hbnext = hb->next;
+ hb->next = new_index[h];
+ new_index[h] = hb;
+ }
+
+ /* Switch to new table */
+ XFREE(MTYPE_HASH_INDEX, hash->index);
+ hash->size = new_size;
+ hash->index = new_index;
+
+ /* Ideally, new index should have chains half as long as the original.
+ If expansion didn't help, then not worth expanding again,
+ the problem is the hash function. */
+ losers = 0;
+ for (i = 0; i < hash->size; i++)
+ {
+ unsigned int len = 0;
+ for (hb = hash->index[i]; hb; hb = hb->next)
+ {
+ if (++len > HASH_THRESHOLD/2)
+ ++losers;
+ if (len >= HASH_THRESHOLD)
+ hash->no_expand = 1;
+ }
+ }
+
+ if (losers > hash->count / 2)
+ hash->no_expand = 1;
+}
+
/* Lookup and return hash backet in hash. If there is no
corresponding hash backet and alloc_func is specified, create new
hash backet. */
@@ -69,14 +115,19 @@ hash_get (struct hash *hash, void *data, void * (*alloc_func) (void *))
unsigned int key;
unsigned int index;
void *newdata;
+ unsigned int len;
struct hash_backet *backet;
key = (*hash->hash_key) (data);
index = key & (hash->size - 1);
+ len = 0;
- for (backet = hash->index[index]; backet != NULL; backet = backet->next)
- if (backet->key == key && (*hash->hash_cmp) (backet->data, data))
- return backet->data;
+ for (backet = hash->index[index]; backet != NULL; backet = backet->next)
+ {
+ if (backet->key == key && (*hash->hash_cmp) (backet->data, data))
+ return backet->data;
+ ++len;
+ }
if (alloc_func)
{
@@ -84,6 +135,12 @@ hash_get (struct hash *hash, void *data, void * (*alloc_func) (void *))
if (newdata == NULL)
return NULL;
+ if (len > HASH_THRESHOLD && !hash->no_expand)
+ {
+ hash_expand (hash);
+ index = key & (hash->size - 1);
+ }
+
backet = XMALLOC (MTYPE_HASH_BACKET, sizeof (struct hash_backet));
backet->data = newdata;
backet->key = key;
diff --git a/lib/hash.h b/lib/hash.h
index a6dd5319..920c6685 100644
--- a/lib/hash.h
+++ b/lib/hash.h
@@ -22,7 +22,8 @@ Boston, MA 02111-1307, USA. */
#define _ZEBRA_HASH_H
/* Default hash table size. */
-#define HASHTABSIZE 1024
+#define HASH_INITIAL_SIZE 256 /* initial number of backets. */
+#define HASH_THRESHOLD 10 /* expand when backet. */
struct hash_backet
{
@@ -44,6 +45,9 @@ struct hash
/* Hash table size. Must be power of 2 */
unsigned int size;
+ /* If expansion failed. */
+ int no_expand;
+
/* Key make function. */
unsigned int (*hash_key) (void *);