[C] Common hash functions. (aeron-io#1178)

* [C] Fix includes.

* [C] Simply mask out the key_hash_code in the *_to_ptr_hash_map since they already use FNV-1a hash function.

* [C] Add 64 bit hash functions.

* [C] Fix includes.

* [C] Use `aeron_hash_64` for all hashmaps.

* [C] Increase default load factor to 0.65.

* [C] Fold 64 bit hash into 32 bit value to retain entropy of the higher bits when masking.

Author: vyazelenko

aeron-client/src/main/c/CMakeLists.txt

@@ -41,6 +41,7 @@ endif ()
 set(SOURCE
     collections/aeron_array_to_ptr_hash_map.c
     collections/aeron_bit_set.c
+    collections/aeron_hashing.c
     collections/aeron_int64_counter_map.c
     collections/aeron_int64_to_ptr_hash_map.c
     collections/aeron_int64_to_tagged_ptr_hash_map.c
@@ -103,6 +104,7 @@ set(SOURCE
 set(HEADERS
     collections/aeron_array_to_ptr_hash_map.h
     collections/aeron_bit_set.h
+    collections/aeron_hashing.h
     collections/aeron_int64_counter_map.h
     collections/aeron_int64_to_ptr_hash_map.h
     collections/aeron_int64_to_tagged_ptr_hash_map.h

aeron-client/src/main/c/collections/aeron_array_to_ptr_hash_map.h

@@ -24,6 +24,7 @@
 #include "util/aeron_bitutil.h"
 #include "util/aeron_strutil.h"
 #include "util/aeron_error.h"
+#include "collections/aeron_hashing.h"
 #include "collections/aeron_map.h"
 #include "aeron_alloc.h"
 
@@ -54,9 +55,9 @@ inline uint64_t aeron_array_hash(const uint8_t *arr, size_t length)
     return aeron_fnv_64a_buf((uint8_t *)arr, length);
 }
 
-inline size_t aeron_array_to_ptr_hash_map_hash_key(uint64_t key, size_t mask)
+inline size_t aeron_array_to_ptr_hash_map_hash_key(uint64_t key_hash_code, size_t mask)
 {
-    return (size_t)((key * 31) & mask);
+    return aeron_hash(key_hash_code, mask);
 }
 
 inline bool aeron_array_to_ptr_hash_map_compare(

aeron-client/src/main/c/collections/aeron_bit_set.c

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include "aeron_bit_set.h"
+#include "collections/aeron_bit_set.h"
 
 extern int aeron_bit_set_stack_alloc(
     size_t bit_set_length, uint64_t *static_array, size_t static_array_len, aeron_bit_set_t *bit_set);

aeron-client/src/main/c/collections/aeron_hashing.c

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2014-2021 Real Logic Limited.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "collections/aeron_hashing.h"
+
+extern uint32_t aeron_hash_code(uint64_t value);
+
+extern size_t aeron_hash(uint64_t value, size_t mask);
+
+extern size_t aeron_even_hash(uint64_t value, size_t mask);

aeron-client/src/main/c/collections/aeron_hashing.h

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2014-2021 Real Logic Limited.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef AERON_HASHING_H
+#define AERON_HASHING_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+inline uint32_t aeron_hash_code(uint64_t value)
+{
+    uint64_t x = value;
+
+    x = (x ^ (x >> 30u)) * UINT64_C(0xbf58476d1ce4e5b9);
+    x = (x ^ (x >> 27u)) * UINT64_C(0x94d049bb133111eb);
+    x = x ^ (x >> 31u);
+
+    return (uint32_t)x ^ (uint32_t)(x >> 32u);
+}
+
+inline size_t aeron_hash(uint64_t value, size_t mask)
+{
+    uint32_t hash = aeron_hash_code(value);
+    return (size_t)(hash & mask);
+}
+
+inline size_t aeron_even_hash(uint64_t value, size_t mask)
+{
+    uint32_t hash = aeron_hash_code(value);
+    hash = (hash << 1u) - (hash << 8u);
+    return (size_t)(hash & mask);
+}
+
+#endif //AERON_HASHING_H

aeron-client/src/main/c/collections/aeron_int64_counter_map.c

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include "aeron_int64_counter_map.h"
+#include "collections/aeron_int64_counter_map.h"
 
 extern size_t aeron_int64_counter_map_hash_key(int64_t key, size_t mask);
 

aeron-client/src/main/c/collections/aeron_int64_counter_map.h

@@ -22,6 +22,7 @@
 
 #include "util/aeron_platform.h"
 #include "util/aeron_bitutil.h"
+#include "collections/aeron_hashing.h"
 #include "collections/aeron_map.h"
 #include "aeron_alloc.h"
 
@@ -38,9 +39,7 @@ aeron_int64_counter_map_t;
 
 inline size_t aeron_int64_counter_map_hash_key(int64_t key, size_t mask)
 {
-    uint64_t hash = ((uint64_t)key << UINT64_C(1)) - ((uint64_t)key << UINT64_C(8));
-
-    return (size_t)(hash & mask);
+    return aeron_even_hash((uint64_t)key, mask);
 }
 
 inline int aeron_int64_counter_map_init(
@@ -78,7 +77,6 @@ inline void aeron_int64_counter_map_delete(aeron_int64_counter_map_t *map)
 inline int aeron_int64_counter_map_rehash(aeron_int64_counter_map_t *map, size_t new_entries_length)
 {
     size_t mask = new_entries_length - 1;
-    map->resize_threshold = (size_t)((new_entries_length / 2) * map->load_factor);
 
     int64_t *tmp_entries;
 
@@ -114,6 +112,7 @@ inline int aeron_int64_counter_map_rehash(aeron_int64_counter_map_t *map, size_t
 
     map->entries = tmp_entries;
     map->entries_length = new_entries_length;
+    map->resize_threshold = (size_t)((new_entries_length / 2) * map->load_factor);
 
     return 0;
 }

aeron-client/src/main/c/collections/aeron_int64_to_ptr_hash_map.h

@@ -22,6 +22,7 @@
 #include "util/aeron_platform.h"
 #include "util/aeron_bitutil.h"
 #include "util/aeron_error.h"
+#include "collections/aeron_hashing.h"
 #include "collections/aeron_map.h"
 #include "aeron_alloc.h"
 
@@ -38,7 +39,7 @@ aeron_int64_to_ptr_hash_map_t;
 
 inline size_t aeron_int64_to_ptr_hash_map_hash_key(int64_t key, size_t mask)
 {
-    return (size_t)(((uint64_t)key * 31u) & mask);
+    return aeron_hash((uint64_t)key, mask);
 }
 
 inline int aeron_int64_to_ptr_hash_map_init(

aeron-client/src/main/c/collections/aeron_int64_to_tagged_ptr_hash_map.h

@@ -23,6 +23,7 @@
 
 #include "util/aeron_platform.h"
 #include "util/aeron_bitutil.h"
+#include "collections/aeron_hashing.h"
 #include "collections/aeron_map.h"
 #include "aeron_alloc.h"
 
@@ -50,7 +51,7 @@ aeron_int64_to_tagged_ptr_hash_map_t;
 
 inline size_t aeron_int64_to_tagged_ptr_hash_map_hash_key(int64_t key, size_t mask)
 {
-    return (size_t)(((uint64_t)key * 31u) & mask);
+    return aeron_hash((uint64_t)key, mask);
 }
 
 inline int aeron_int64_to_tagged_ptr_hash_map_init(

aeron-client/src/main/c/collections/aeron_map.h

@@ -17,7 +17,7 @@
 #ifndef AERON_AERON_MAP_H
 #define AERON_AERON_MAP_H
 
-#define AERON_MAP_DEFAULT_LOAD_FACTOR (0.55f)
+#define AERON_MAP_DEFAULT_LOAD_FACTOR (0.65f)
 
 #include <stdint.h>