Keep rehashing if dist_from_ideal_bucket is > DIST_FROM_IDEAL_BUCKET_LIMIT during insertion (fix issue #52)

During insertion a check was done on dist_from_ideal_bucket to be sure
it doesn't becomes bigger than DIST_FROM_IDEAL_BUCKET_LIMIT but this was
only done during the robin swap. A check should also be done beforehand
if we find an empty bucket otherwise the variable could overflow and
lead to bugs. This commit adds this check.

Author: Tessil

include/tsl/robin_hash.h

@@ -1231,7 +1231,7 @@ class robin_hash : private Hash, private KeyEqual, private GrowthPolicy {
       dist_from_ideal_bucket++;
     }
 
-    if (rehash_on_extreme_load()) {
+    while (rehash_on_extreme_load(dist_from_ideal_bucket)) {
       ibucket = bucket_for_hash(hash);
       dist_from_ideal_bucket = 0;
 
@@ -1293,7 +1293,7 @@ class robin_hash : private Hash, private KeyEqual, private GrowthPolicy {
     while (!m_buckets[ibucket].empty()) {
       if (dist_from_ideal_bucket >
           m_buckets[ibucket].dist_from_ideal_bucket()) {
-        if (dist_from_ideal_bucket >=
+        if (dist_from_ideal_bucket >
             bucket_entry::DIST_FROM_IDEAL_BUCKET_LIMIT) {
           /**
            * The number of probes is really high, rehash the map on the next
@@ -1379,8 +1379,11 @@ class robin_hash : private Hash, private KeyEqual, private GrowthPolicy {
    *
    * Return true if the table has been rehashed.
    */
-  bool rehash_on_extreme_load() {
-    if (m_grow_on_next_insert || size() >= m_load_threshold) {
+  bool rehash_on_extreme_load(distance_type curr_dist_from_ideal_bucket) {
+    if (m_grow_on_next_insert ||
+        curr_dist_from_ideal_bucket >
+            bucket_entry::DIST_FROM_IDEAL_BUCKET_LIMIT ||
+        size() >= m_load_threshold) {
       rehash_impl(GrowthPolicy::next_bucket_count());
       m_grow_on_next_insert = false;