Revert "[map] Implement Robinhood hashing"

This reverts commit 7056178568.

src/hb-algs.hh

@@ -314,7 +314,7 @@ struct
   template <typename T> constexpr auto
   impl (const T& v, hb_priority<2>) const HB_RETURN (uint32_t, hb_deref (v).hash ())
 
-#if 1
+#if 0
   // The following, unfortunately, while keeps the probing chains short, slows
   // down the overall hash table performance. Not because of the extra operation
   // itself in my opinion, but something else going on that we have not been able

src/hb-map.hh

@@ -200,46 +200,22 @@ struct hb_hashmap_t
     return true;
   }
 
-  unsigned
-  probe_distance (unsigned i, unsigned hash) const
-  {
-    return (i + mask + 1 - (hash % prime)) & mask;
-  }
-
   template <typename KK, typename VV>
   bool set_with_hash (KK&& key, uint32_t hash, VV&& value)
   {
     if (unlikely (!successful)) return false;
     if (unlikely ((occupancy + occupancy / 2) >= mask && !resize ())) return false;
 
-    K k = std::forward<KK> (key);
-    V v = std::forward<VV> (value);
-
     hash &= 0x3FFFFFFF; // We only store lower 30bit of hash
     unsigned int i = hash % prime;
-    unsigned dist = 0;
     while (items[i].is_used ())
     {
-      if (items[i].is_tombstone ())
-        break;
       if ((hb_is_same (K, hb_codepoint_t) || items[i].hash == hash) &&
-	  items[i] == k)
+	  items[i] == key)
+        break;
+      if (items[i].is_tombstone ())
         break;
-
-      // Robinhood hashing
-      // https://www.sebastiansylvan.com/post/robin-hood-hashing-should-be-your-default-hash-table-implementation/
-      unsigned existing_dist = probe_distance (i, items[i].hash);
-      if (existing_dist < dist)
-      {
-        hb_swap (items[i].key, k);
-        //hb_swap (items[i].hash, hash);
-	uint32_t tmp = items[i].hash; items[i].hash = hash; hash = tmp;
-        hb_swap (items[i].value, v);
-	dist = existing_dist;
-      }
-
       i = (i + 1) & mask;
-      dist++;
     }
 
     item_t &item = items[i];
@@ -251,8 +227,8 @@ struct hb_hashmap_t
 	population--;
     }
 
-    item.key = std::move (k);
-    item.value = std::move (v);
+    item.key = std::forward<KK> (key);
+    item.value = std::forward<VV> (value);
     item.hash = hash;
     item.set_used (true);
     item.set_tombstone (false);
@@ -308,12 +284,9 @@ struct hb_hashmap_t
     if (unlikely (!items)) return nullptr;
 
     hash &= 0x3FFFFFFF; // We only store lower 30bit of hash
-    unsigned i = hash % prime;
-    unsigned dist = 0;
+    unsigned int i = hash % prime;
     while (items[i].is_used ())
     {
-      if (dist > probe_distance (i, items[i].hash))
-        return nullptr;
       if ((hb_is_same (K, hb_codepoint_t) || items[i].hash == hash) &&
 	  items[i] == key)
       {
@@ -323,7 +296,6 @@ struct hb_hashmap_t
 	  return nullptr;
       }
       i = (i + 1) & mask;
-      dist++;
     }
     return nullptr;
   }